HOW PROGRAMMABLE DIGITAL FUEL ANDTIMING SYSTEMS WORK

Programmable engine management systems permit (and require)a user to calibrate the basic raw fuel and ignition curves for anengine by defining tables of numbers that specify spark timingadvance and base fuel delivery for pulse width-modulated(P\7M) electronic fuel injection as a function of engine speedand airflow. Such tables are typically represented to the user(tuner, calibrator) in graphical or tabular format via user inter-facelediting sofware running on a'Windows computer (usually

a battery-powered laptop).This PC-based engine management software simultane-

ously controls communications-driver software that has the abil-ity to interact, via serial data cable, with the onboard electroniccontrol unit (ECU) that actually manages the spark and fuelrequirements for an engine. The sofrware allows the user tomove data back and forth berween ECU memory and the lap-top for tuning purposes.

Typically, programmable engine management systems pro-vide both the abiliry to interactively modify many operatingparameters and table cells in the ECU while the engine is run-ning, as well as the abiliry to upload the entire set of all enginemanagement tables into a'Windows PC for subsequent offlinecalibration and eventual download back to the same or alterna-tive ECU(s).

A programmable engine management system is, therefore,comprised of the onboard ECU, firmware, and calibrationdata, plus a'S7'indows laptop computer (or, in a few cases, analternate dedicated interface module), laptop engine manage-ment sofrware, and data-link hardware. For full functionalityof the system, all components must be present and opera-tional. Once the ECU is calibrated, it is fully self-containedand will run the engine without additional components. How-ever, without the laptop present and connected, the ECU is inno sense programmable.

Although user-interface soffware of various engine manage-ment systems may present internal engine management tables tothe tuner with its own unique graphical appearance-andalthough the underlying resolution or granularity of the tablesmay, in fact, actually vary-behind the scenes the basic enginemanagement operating concepts are exactly the same: \When it isapproaching time for the digital microprocessor managing anengine to schedule the next fuel injection or spark event, theprocessor first checks engine sensor data to get a snapshot of howfast the engine is turning and how much air it is ingesting.

The ECU then performs a series of look-ups to the appro-priate entry for the current speed and airflow in the various fueland timing tables to determine when to open and close the injec-tor(s) to spray a pulse of fuel into one or more cylinders and howmany degrees before top dead center to trigger an external ignit-er or coil to fire the next spark plug. If engine speed or loadingfall somewhere in between rwo specified points in an enginemanagement table, the ECU will provide base fuel or spark orcorrections by applying a weighed average of the closest severalpoints on either side of the actual value.

Regardless of the exact means used, the process of calibrat-ing an engine management system on a new engine has the ulti-mate goal of optimizing torque, fuel economy, or emissions ateach and every breakpoint ofengine speed and loading definedin the fuel and ignition tables (there are usually berween 24 and800 such points).

In theory, this can be a laborious process, but it is one thatcan frequently be expedited with the use of automated map-builder computer modeling algorithms, pre-existing calibrationsfrom similar engines, intelligent extrapolation and interpolationberween rpm ranges and load points, and even self-learning rou-tines that make use of wideband O, sensors and dynamometers.Nevertheless, it is worth keeping in mind that OEM carmakersfrequently spend months or evenlears calibrating the engine man-agement systems for a particular engine in a particular vehicle.

J oh n C a rm a c k's twin-tu rboFerrari F50 on the NorwoodDynojet, getting ready for a Carand Driver magazine testingregime. Bob Norwood tweakedthe Ferrari's Bosch Motronicsystem at lower power settings,but when it came time to crankup the boost to higher levels onthe $750,000 vehicle's 10.5:lcompression 60-valve V-12, theFerrari converted to Motec EMSfor ultimate control.

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Simple Digital SystemsTo tune a running engine tlat has an unfamiliar engine manage-ment sysrem without making rhings worse or risking damage rothe engine while you learn, youte going to need to gain a work-ing familiariry with the engine management soflnuare rhat enablesyou to quickly grasp whar is happening and then react quickly.You definitely do nor wanr to be rying to read the manual to findout what to do when detonation or thermal loading is threaten-ing a meltdown on your new hot rod powerplant. And for that,youre going to need patience, judgment, and experience with thesoftware and ECU data structures, as well as familiariry with thedatalogging sofrware you will dzf.nitely need in order to cdibratepower-adder engines in boosted-power ranges.

The abiliry to work fast without making stupid misrakes isimportant, because running engines do not necessarily remain ina stead-y state: They heat-soak in all sorts of interesting ways thatcan affect the tuning and power. The oil gers thinner.-Resistanceto detonation degrades. Engines in a dyno cell pollute the air withhydrocarbons, carbon monoxide, and heat, which affects intakeair temperarure, volumetric efficiency, intercooler efficiency,combustion qualiry and other running paramerers. The abiliry toreact quickly is important for reasonable tuning efficiency. Oncean engine warms up out of a certain range on the warm-up enrich-ment map, for example, ir will probably be hours before it coolsoff enough to give you another crack at calibradng rhe colderstart-uP temPerarure ranges.

If you're buying dynamometer time for tuning, slow tun-ing abilities can be cosrly. Slow reaction time can even be dan-g€rous. A poor state of tune can damage the engine if it takesthe tuner too long to recognize and figure out how ro correcrthe problem, or if the correction is in the wrong direction. AsRay Kurzweil points out in The Age of Spiritual Machines,human beings are lightning-fast at recognizlng a parrern andtaking specific preplanned action (like realizing a kid has run infront of your car and hitting the brakes), bui we think quite

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An afternative to the laptop is a dedicated programmer module likethis user intefface from sDS or a similar unit from Edetbrock and oneor two other firms. You can accomplish most of the functionality of alaptop, but you are peering through a tiny window into the EMSenvironment. 0f course, once the system is calibrated, the userinterface is of no consequence when driving.

slowly when faced with new situarions that call for reasoningthrough a problem.

To calibrate mosr programmable engine managemenr sys-tems, you will first need to have at least some familiariry with theoperating environment of a \Tindows laptop PC. In the firstplace, you're going to have to install the EMS sofrware that you'llbe using to interface to the onboard engine management sysremin order to calibrate engine control tables and parameters. Later,you will need ro use rhe laptop keyboard to enrer configurationdata and ro use the arrow keys or pointing device (mouse, track-point, and so on) to change the shape or height of fuel and igni-tion graphs, and so on.

Once the sofrware is up and running, you'll need sufficientfamiliariry with a given engine management sofrware environ-ment to be able to dynamically track (while the engine is run-"i$) which portions of the main fuel, main ignition,cold-running, and transienr enrichmenr maps are being used bythe engine management sysrem to manage ihe engine.Virtuallyall engine managemenr systems provide some kind of engine datapage that can be used to monitor engine sensor values ".td act,r-ator commands (such as currenr injection pulse width and igni-tion timing), and determine the map table cells and correctionscurrently being used in the engine management calculations.

The main fuel, main ignition, engine temperarure compen-sation and other tables rypically provide some sorr of highlight-ing, bolding, pointer, or other indication of which cell oi gophis the current one in a particular table. Many sysrems have somesort of trot key that a runer can press ro instantly jump to thecurrently acrive map or map cell for immediate editing.-

!o yoqte going ro have to practice working witli the userinterface of the EMS software and calibrating ih. p"r"-.t..,and tables.

The trouble is, even if you understand the sofrware envi-ronment, you still have to have tuning skills and diagnostic toolsto do the job well. Professional runers persistently iomplain ofcomputer-savvy customers with editing access ro programmableengine management systems and linle or no tuning experience.

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VIRTUAL CARBURETORSSome old-timers and bike tuners have a lot of experience tun-

ins carbureted engines, and they know a lot about how people

ffiil;;l;;s b.f|re rhere were fart .*h",r.t gas analyzers, wide-

band airifuel-ratio meters, or affordable chassis dynos. This can

be dangerous.It is certainly true that a good basic knowledge of how and

*hy;;gi;;, ,"t. f,t.t ".,d sp",f timing at variousspeed and load-

irrj r"n[., is important. It is also true-a lot of carbureted engines

*Jr..rt"operating atavery accurateand high state of tune' The

mixture iistribuiio' b.r*..n cylinders was often terrible, with

,"-. ,irgfe carb cylinders .,rrrning much leaner than others and

i""i"f.Ff"rts directed toward -iki.tg sure the leanest cylinders

were running safelY rich.\7hat's -or., the specific Power (horsepower Per cubic

inch) of musclecar-.r" p.,fo'-""tt engines was vastly less

than recent sPort-compact et'gines, and even the gross horse-

fo*., *", of,.., l.sr. Thtti are plenty of t'a-[9r tur-'bo.h"rg.d

Hondas making more horiepower than a 1970 426

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h i gh-o utp ut p owerplarrts, b",,t-fortunately o r un fortunately-

polrr,, igrritio.r, "rrd ."rburetors targeted by T1"yf":tYrers for

specific engines were' practically ipeaking' limited in their

;'d;;;.;i3- leopt. *o.tld adjusi idie-air-screws to set airlfuel

mixture at idle, and they mightswap main jets around a little to

*. fo, best acceleration ne-ar wide-open throttle, but they were

l.*lik.ly to make radical changes to basic components like ven-

iuri, ,t ", greatly affect midrange .airlfuel ratios' tVhere they

-"J. .h"n!.r, these were likely Io be incremental' in ways that

affected oni particular area of th. timing or fuel curve and that

left alone the-basic shape or slope of a fuel or timing curue'^

There *... .r.u.', many."rb,rr.t.d turbo motors (for really

good ,."rons), and withoui the requirement to deal with boost-

3d .ngi.r.r, hot rodders tended to follow a cookbook approach

,o p.r"fo.-ance tuning for- specific normally aspirated-perform-

"tJ. .tgirres. For, ."1-p1., "a slock compression 350 Chevy

moror with a com cams xl grind, x2-inch tube headers, and a

Holley x3 carb needs Holley "*4

^ 'njets, x5 Power valve' with

the accelerator PumP rod in the x6 position' and you need x7

cenuifugal ad.r".r.e sp.ingr in your distributor and x8-degrees

total timing."

Jet-swipping is smelly, time-consuming' and costs actual

."rhj-o..y'fo, ih. p..cirely machined jets (unlike key strokes

;;; .;;p.rt.r, *hi.h are free), so tuners were less likely to make

ii. kindr'of radical changes that would completely screw lP

fuel

J.irt.ty. Bo,,o- line, ii the old days it iook real work and

moneFto royally screw up physical engine management systems'

so it did.rt h"pp." ", -.r.h ", it does today when computers have

;;;rry ;.r."lla the efficiency with which people..can radicallv

3lr.*'rrp electronic engine management system calibrations'

One trend in englne -"n"gi^.nt modifications is what I

like to call the ".'irt,'r""I ."rb,,"t-o'," that is' modifring a stock

engine management system for power-adder conversions to fix

U"[ OEV1 bJhavior with a potentiometer-equipped electronic

i",.t..p,"t box that gi't'es a tuner the semi-automated option

;il;ilg selected rubi.t, of the fuel and timing 9lrves by turn-

i"* " f.rr"oU-and without the challenge of building a scratch

.;il;d." equal to the factory's. Comp-anies like Techlusion do

a sreat iob of providing the abiliry to make incremental changes

;"?;;,.4- "t ,p..ifi. "r".", of injiction and timing' keeping-it

,irriple "nd piot..ting people from themselves-just like in the

old days.

126^

HOWTO HIRE SOMEONE ELSE TO DOTHECALIBRATION/TUNING

Many performance shops pride themselves on their engine man-

"g;.i, problem-soluing abilities' They love it (perhaps secret-

lfi *h..t ih.y g., a.h".r|. to be a hero, fixing a problem created

du " .,rr,o-.iot (even better) a competing performance shop'

eipecially if it involves selling expensive new Parts or equrPment'"\if.'ll hau. to change out tf,e Framajigger for a'Whatsahoosits;

a Framajigger isn't *:orth a damn and could never work on your

i q r i lr'ttilbeere Super-60-powered trike. Squirrel. Performance

shouli never have installed it, but since they're under 60 counts

oi fr",ra and a death sentence for incompetence, you get what

you pay for."' Performance tuners can be very good at looking you in the

eye and conveying absolute certainry about their ability to

".hi..r. lo*-."rih-Jrbit with a l9l2 John-Deere-powered trike'

."." if they aren't actually sure what one is' Many Performance

rhopt h"u. " very hard time turning down targets of opportuni-

| ,it", ar. outriie their ordinary specialization and expertise'

The deadly combination of pride and greed can lead to

shops taking on tuning projects^that, by definition' require on-

,[.];ob ,r"iiirrg (or d"usting -off old exPertise on systems they

h"u.rrt seen in ""

long time)]Some shops welcome the chance to

g.. p"ia to learn .nJ* engine management system' *!:h could

result in unnecesr".y p"rl and equipment changes' The worst

o.rr.o-. would be if'a shop damagtd yout engine or vehicle

working on a system with a steep learning.cu.rve'

Tlie follo*ing are some rules of thumb that can help you to

avoid this sort of heartache:. I would not use a tuning shop that lacked extensive experience

*i,h ;;* specific e.,ginJ-"r"g.-.nt system. Preferably, they

should be a dealer.. unless the tuner were a wizard who I knew to be a wizard, I

would probably wanr references from satisfied customers. other

customers can verif' satisfaction with a tunert technical expert-

ise. and customers will also have opinions about suPPort caPa-

bilities, financial policies, and fairness'. I would l.rot .ror-"lly use a tuning shop for engine manage-

ment calibration that'did not have its own in-house chassis

&;;-;;.ter. Under exceptional circumstance, this rule might

b! modified if a runer had a close working arrangement with a

;t;; th;t ihat did have a dynamomett'' Vt', it is possible to do

"!""a r,rrrirrg job with a straP-on (no' not thatkindof strap-on!)

"i.lero-.,.i-ryp. pr..rdo-dyno fifth-wheel device (that is, G-

T.ch) and a poi "Ut. wideband airlfuel-ratio meter (or an engine

management system that supports a wideband O, sensor)' or' at

" *irii-,rnl, #th a wideband AFR meter and a bunch or desert-

ed road. However, I am more comfortable with a shop that has

made the investment in a $20,000-plus dynamometer than one

that has not. \what's more, a shop th"t o*.tt the dyno does not

h"rr. ,o buy dyno time, so you're likely to get more extensive dyno

"*t, "rri prob"bly a better calibration than a situation where

yor'rt i.tt.t is on the clock.. Possession of an engine dyno (for example, a Superflow) test cell

is a leading indicatolof griat seriousness. You can drive a car onto

a chassis f,y.ro "rrd rip off a pull or rwo in a few minutes; an

engine dyno is ,,'or. .orrrplicaied' It was somewhat easier in the

a"i, "f carbureted distributor-ignition engines but attaching a

i,rll-in1..,.d powerplant to an ingine dyto. and connecting or

f"U.i."ti.rg .rrirythi"g it takes to make it work outside the engine

bay of a Jar ryp\rally"takes ho.urs' However, when they calibrate

."ii"o in Deiroit or Munich or Japan or wherever, they start

wiih radically expensive warer-brake or eddy-current engine

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issue ahead of time and come to an agreemenr. If it would be cat-astrophic if your engine breaks, make sure the runer understandsthis. A tuner might work differently-more carefully, fartherfrom the ragged edge-if it is essential to avoid damage versus ifthe highest prioriry were to search for the absolute limits of deliv-erable maximum power.

The bottom line is that the reason faaory engines often havethe capabiliry to be hot rodded to higher power levels is thatautomakers must warranr them and therefore always design themto run at power levels a conservatively safe distance frommechanical and thermal damage. Actually, in the distant past,back in the 1960s, there were a few vehicles sold by automakersfor street or track use without uarranty for racing use with radi-cal hairy engines like Chrysl er's 426-ci Race HemI, Fordt SOHCCammer 427, and a few others. Today all streetable vehicles haveto pass emissions and have warranties, and no one sells anythingwithout a warranry.

Basically, if something breaks on the dyno while tuning andit is clearly the tunerk fault through egregious negligence, rhetuner may want to fix it to protect his reputarion. If this hap-pened essentially through dishonesry or fraud (he sold you junkthat was bound to break or to break the engine in your applica-tion), you could sue him, and maybe you'd win. And if you won,maybe there'd be something to take. But those are big ifs.

The best insurance is to find a good, experienced tuner witha good reputation, tools, and financial resources. Pay his highprices and expect him to do his best for you.

And if something goes wrong that is beyond his and yourcontrol, tell yourself,

"Thatt racing."

ENGINE TUNING THEORYTo tune an engine effectively, you will need ro understand thetheory of volumetric efficiency, burn rate, spark advance, airlfuelratios, temperature, air-pressure, detonation, and fuels.

VOLUMETRIC EFFICIENCYAND ENGINE FUEL REOUIREMENTS

A piston engine is, in a sense, a self-propelled air pump thatbreathes in a quantiry of air through the throttle related to thedisplacement of the engine, and exhales nitrogen and combus-tion products through the exhaust. But even ar wide-open throt-tle (WOT), the amount of air that enters a spark-ignition pistonengine varies considerably depending on-sruff. There are manyfactors that affect how much air actually enrers the engine's cylin-ders under various operating conditions (almost alwalys less ihanthe static displacement of the engine excepr with highly opti-mized performance engines utilizing resonarion-effects tunedintake and exhaust systems, or on turbo or supercharged engines,which may easily operate at 100 percenr or more of static dis-placement, also known as the uolumetic efi.cienqt or VE).

Torque is the instantaneous rwisting force that an internal-combustion engine is able to impart to a crankshaft, averaged overthe combustion cycle by a flywheel. Over time, torque can be usedto do work such as accelerating a car. Peak rorque occurs at theengine speed and loading at which an engine (with power-adders,if present) is most efficient at ingesting air into the cylinders.Therefore, peak torque is also peak uolumetric fficienry, or YE.Peak torque requires the largest amount of fuel per combustioncycle, hence, the longest injector open-time or pulse width. Eventhough engine breathing is less efficient at speeds above peaktorque and therefore each putt is less powerful, more combustionevents are occurring per time, and the engine will make its peakpower at faster speeds than peak torque. Due to the definition of

power as a function of torque 15,250, these two measuremenrs arealways the same at 5,250 rpm. A properly tuned engine willalways use the most fuel per rime at peak power.

On modern normally aspirated srreer engines, engineersstrive to design engines to have as high a VE (torque) as possi-ble across the range of engine operating speeds. One hundredpercent VE is the amount of air that would be in the cylinderof an engine at bottom dead center at resr, minus the combus-tion chamber clearance volume (the displacement of theengine). It is extremely difficult or impossible to achieve 100percent VE when the engine is running, because it takes a cer-tain amount of time for air to rush into the cylinders, and thereis a limited amount of time (eight or nine thousandths of a sec-ond at 7,000 rpm), and there are resrricrions in the way. Moststreet piston engines cannor achieve anything like 100 percenrVE, settling instead for maybe 70 to 90 percent, but engineerswork to build a high, flat torque/VE curve across the rpm range.

A number of factors conspire to prevent a full 100 VE innormally aspirated srreet engines. There is normally at least aslight pressure drop through a throttle body or carburetor,even at wide-open throttle (particularly with a carb due to theneed for a restricting venturi). All carburetors and fuel injec-tion throttle bodies restrict airflow-producing a pressuredrop-when the throttle blade is partially closed (and some-times even when it's wide open). Intake ports and valves offerat least some restriction at some engine speeds. The exhauststroke does not expel all burned gases because some exhaust istrapped in the clearance volume. The exhaust valves andexhaust pipes offer some restriction as well. The camshaft pro-file of an engine has a huge effect on rhe VE of an engine atvarious speeds and loading.

If a normally aspirated engine had a perfectly flat torquecurve across the rpm range, injection pulse width would notvary at all with engine speed, but would be a function only ofengine loading. If VE is entirely independent of engine speed,then the amounr of air entering a cylinder on the intake strokewill depend entirely on the amounr of air pressure in the intakemanifold, hence, injection pulse width is a linear function vary-ing precisely with the voltage from a manifold absolute pressuresensor, with peak VE and rorque at the highest achievable man-ifold pressure. Since many modern srreet engines do have a prer-

ry flat torque curve, a calibration in which pulse width varies ina linear fashion from zero atzero manifold pressure to maximumpower pulse at full achievable manifold pressure is a goodapproximation of an ideal steady-state airlfuel table optimizedfor peak power.

Given the varying VE of an engine, rhe amount of air in thecylinder at any given breakpoint is not perfectly predictable.Again, you can assume that the maximum VE occurs at the pointof peak torque. This will be the point of maximum injectionpulse width, with pulse width falling off both above and belowthis. Maximum power will occur at a higher rpm than peaktorque where the engine is making more power strokes per timeincrement, although the power strokes are less efficient at speedsabove the torque peak and will therefore require less fuel to beinjected per power stroke.

In some cases, engine rorque and VE vary considerably withrpm. Normally aspirated engines optimized to run efficiently atvery high speed with resonarion-effects intake-runner andexhaust tuning at the expense of very weak low-rpm rorquecapabilities are one example. Some such engines have achieved asmuch as 10 psi positive pressure at the intakevalve from inertialand resonation effects. Anorher example of varying VE is

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160 psi compression pressure rises quickly to over 600 psi fol-lowing combustion. Pressure rise rates can exceed 20 psi perdegree of crankshaft rotation. Cylinder pressures are highest atwide-open throttle and are lowest at idle and light cruise, whenintake manifold vacuum is very high and engine VE very low.Combustion proceeds faster under higher compression.

Turbulence is carefully designed into combustion chambers.Some swirl will produce greater flame speed, more efficient com-bustion, and even help resist knock by spreading the flame frontmore quickly. Too much swirl will produce undesirable distur-bance of the quench layer around the combustion chamber,increasing heat loss into the cylinder walls.

The actual performance of fuel in an engine is closely relat-ed to the release of energy in the combustion process. This isaffected by dissociation of the reactants and products of com-bustion (splitting of molecules into smdler molecules or singleatoms or ions) and heat transfer through the combustion cham-ber. Increased heat in the combustion chamber makes power, butheat can also be pro-knock. At wide-open throttle at high speed,heat transfer amounts to about 15 percent of the fuelt thermalenergy. This heat loss decreases with increased brake mean effec-tive pressure in the cylinder. The heat transfer is maximized atstoichiometric airlfuel ratios, decreasing with the higher fuel flowrates of rich mixtures. Heat transfer into the block and waterjacket also depends on gas turbulence near the combustionchamber surfaces, and it increases with knock and other violentcombustion conditions.

Given that engines induct a fairly constant mass of air for agiven speed, manifold pressure, camshaft timing, and intake tem-perature, the need to improve spark-ignition engine power forracing has led to two main strategies in an effort to increase theamount of fuel that can be burned in the combustion chamber.The first has been to increase the mass of orygen intake by super-charging or supplementary oxygen injection, mostly in the formof nitrous oxide. The second has been to search for fuels withhigh specific energy.

In addition to the octane number requirement of an enginein order to avoid detonation, high-performance engines haveother performance requirements for fuels, including volatiliryflame speed, weight, and volume.

SPARK ADVANGESpark advance, which is optimally timed to achieve best torqueby producing peak cylinder pressure at about l5 degrees ATDC,increases octane requirements by a half to three-quarters of anoctane number per degree of advance. Spark advance increasescylinder pressure and allows more time for detonation to occur.

Engine speed range and fuel burn characteristics affect igni-tion timing requirements. As an engine turns faster, the sparkplug must fire at an earlier crank position to allow time for agiven airlfuel mixture to ignite and achieve a high burn rate andmaximum cylinder pressure by the time the piston is positionedto produce best torque, which is dependent not only on enginespeed but on mixture flame speed, which, in turn, is dependentnot only on the rype of fuel but on operating conditions thatchange dynamically, such as airlfuel mixture.

Therefore, an independent variable affecting the need forspark advance as rpm increases is the need to modify ignitiontiming corresponding to engine loading and consequentvolumetric efficiency variations, which demand varyingmixtures. Throttle position, for example, affects cylinder filling,resulting in corresponding variations in optimal airlfuel mixturerequirements.

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ECONOMY : Part-throttle

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At high loading and wide-open throttle, richer mixruresgive better power by making sure that all air molecules in thecombustion chamber have fuel presenr to burn. At wide-openthrottle, where the objective is maximum power, all four-cfclegasoline engines require mixtures that fall beween lean andrich best torque, in the 11.5 to 13.3 gasol ine range. Since thisbest t-orque mixrure spread narrows at higher speeds, a goodgoal for naturally aspirated engines is 12.0 to 12.5, p..haptricher if fuel is being used for combustion cooling in aturbo/supercharged engine.

Typical mixtures giving best drivabiliry are in the range of13.0 to 14.5 gasoline-air mixrures, depending on speed and load-ing. At higher engine speeds, reyerse pulsing through a carb inengines with racing cams tends to enrich the mixture as reversiongases pass through the venturi wice. Naturally, this is not a prob-lem with fuel injection.

EFI engines are not susceptible to hot wearher percolation,in which fuel boils in the carb in hot weather when a hot engineis shut down, flooding into the manifold. This is so-.*h"tdependent on the distillation curve of the fuel, which variesaccording to the weather for which it is intended. Hot weatherpercolation can be aggravated by high vapor pressures produced

!f fuel boiling in the fuel pump or fuel lines, forcing additionalfuel past the float needle. Similarly, vapor lock-produced bymechanical fuel pumps supplying a mixture of gas and vapor toa carb and evenrually uncovering the main jets as fuel leveldrops-is not a problem with EFL

The main difference between compurer-controlled enginesand earlier modes of control is that with EFI engines, variaiionsin speed and loading and other engine paramerers translate intospark advance and fueling pulse width values that at any partic-ular point on the spark or fuel map can be completely inde-p_endent of other nearby points (and could vary quite abruptly,if necessary). This was impossible with older mechanical controlsystems. Computer-controlled engines eliminate compromises infueling and spark control. Multi-port injection eliminates distri-bution and inconsistency problems wirh handling wet mixturesin the intake manifold associated with less than one carb percylinder, often resulting in improved cold running, improvedthrottle response under all conditions, and improved fuel econ-omy without drivabiliry problems.

Computer engine management with individual cylinder-adjustable electronic port fuel injection really shines on exrreme-ly high-output engines with high effective compression ratios.Dallas supercar builder Bob Norwood points out that for peakpower, any engine must be treated as a gang of single cylinderengines, each of which should be optimized for peak power.

On NASCAR engines-restricted to single-point carbure-tion-this has been done by cusrom modification of the com-pression ratio, rocker arms, and cam lobes for individualcylinders. But using sequential programmable EFI with fuel andignition calibration on an individual rylinder basis, whatever thevolumetric efficiency of each "single-cylinder

engine," optimaltiming and mixture can be provided by compurer.

Individual cylinder calibration is good for 50 horsepoweron a rypical high-output small-block Chevy V-8, says Norwood.Not only does individual cylinder calibration improve power,but it saves engines from knock damage while allowing a high-er state of tune. By contrast, common practice on street carbu-reted engines or batch fuel injection is ro rune to the leanestcylinder (read best-flowing). A Chevy V-8 with its dog-leg portstvpically varies 10 percent in airflow between best and worsrcvlinder, and it is typical that V-rype morors respond better than

in-line motors to individual cylinder calibration. On a dyno,best and worsr cylinders that are within 100 degrees EGT ofeach other is considered excellent. Leaning or'tt an engine on adyno or track will frequently make more power until iuddenlyone or two cylinders die.

"You always burn one or rwo cylin-

ders," says Norwood. "In the meantime, the other slackers are

running rich." Some advanced engine managemenr sysremshave implemented EGT:feedback closed-loop sysrems thatequalize EGT from all cylinders ar a targer level with individ-ual-cylinder calibration, simultaneously providing best poweracross the board. \X/ith this system, every cylinder can reachmaximum power ar very high compression ratios with the besthigh-octane gasoline.

Testing by Smoky Yunick for Circle Tiack showed that thesmall-block chevy test engine was prone to detonation on threeofthe eight cylinders. This was thought to be due to unequal dis-tribution or coolant circulation that caused those cylinders to runhotter. "Now

we could have cut these three cylinders to l4:l com-pression," writes Smoky, "and

maybe run the other five rylindersat 15:l and gained some power. Dont kno*, but I do know this,you are gonna get a safer, more powerful engine if you adjust thecompression, timing, and distribution to each cylinder."

TEMPERATUREInlet air temperarure increases octane requirements by 0.5 octanenumber per 10 degree increase. Temperature affecrs fuel per-formance in several ways. colder air is denser than horter air,raising cylinder pressure. colder air inhibits fuel vaporization.But hotter air directly raises combustion t.-pet"tutes, whichincreases rhe possibiliry of knock.

EFI systems normally have sensors to read the temperatureof inlet air and adjust the injection pulse width and spark tim-ing to compensare for densiry changes and fuel volatiliry limita-tions. Engines will make noticeably more power on a cold daybecause the cold, dense air increases engine volumetric efficien-cy, filling the cylinders with more molecules of air. This is badnews for a carb, which has no way of compensaring (other thanmanual jet changes-one size per 40 degrees remperarurechange). Piston-engine airplane pilots must always know theambient air temperature in order to estimare take-off distance(much shorter on colder days), and aircraft fuel systems (includ-ing carbureted systems) allow dynamic manual adjustments ofairlfuel mixture. As youd expecr, racing auromotive enginedesigns always endeavor to keep inlet air as cold as possible. Evenstock streer cars often make use of cold-air inlets, since each 1 Idegrees Fahrenheit increase reduces air densiry I percent.

Cold engines require enrichmenr to counreract the fact thatonly the lightest fractions of liquid fuel may vaporize at coldertemperatures while the rest exists as globules or drops of fuel thatare not mixed well with air. The actual vaporization/distillationcurve of various gasolines and fuels differs, depending on thepurpose for which the fuel is designed, and gaseous fuels likepropane and methane do not require cold running enrichmentand have no intercooling effect once in gaseous form. But in acold engine, mosr of a fuel like gasoline-in liquid form-willbe wasted.

Liquid fuels do not vaporize well in cold air (though the oilcompanies do change their gasoline formulation in an effort tocounteract this by increasing the vapor pressure in cold weather,which can lead to a rash of vapor lock in sudden warm spells inwinter). choking sysrems in carbureted vehicles and .old-startfuel enrichmenr sysrems on EFI vehicles are designed to producea rich-enough mixture to run the vehicle e'oen *hen much of the

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in the combustion chamber that can accelerate wear of an engineor actually cause catastrophic failure. Preignition is another formof abnormal combustion in which the airlfuel mixture is ignitedby something other than the spark plug, including glowing com-bustion chamber deposits, sharp edges or burrs on the head orblock, or an overheated spark-plug electrode. Heavy, prolongedknock can generate hot spots that cause surface ignition, whichis the most damaging side-effect of knock. Surface ignition thatoccurs prior to the plug firing is called preignition, and surfaceignition occurring after the plug fires is called post ignition.Preignition causes ignition timing to be lost, and the upwardmovement of the piston on compression stroke is opposed by thetoo-early high combustion pressures, resulting in power loss,engine roughness, and severe heating of the piston crown. It canlead to knock or vice versa. Dieseling or run-on on carburetedengine is usually caused by compression ignition of the airlfuelmixture by high temperarures, bur can be caused by surface igni-tion.

Apparently identical vehicles coming off the same assemblyline can have octane requirements that vary by as much as 10octane numbers. The octane number requirement (ONR) for anengine in a particular vehicle is usually established by making aseries of wide-open-throttle accelerations at standard spark tim-ing using primary reference fuels with successively lower octaneratings until a fuel is found that produces rrace knock.

The single most important inrernal engine characteristicthat requires specific fuel characteristics is compression rario,which generally increases the ONR +3 to +5 per one ratioincrease (in the 8-11:1 compression ratio range). High com-pression ratios squash the inlet airlfuel mixture into a more com-pact, dense mass, resulting in a faster burn rate, more heating,less heat loss into the combustion chamber surfaces, and conse-quent higher cylinder pressure. Tirrbochargers and superchargersproduce efectiue compression ratios far above the nominal com-pression ratio by pumping additional mixture into the cylinderunder pressure. Either way, the result is increased densiry of airand fuel molecules that burn faster and produce more pressureagainst the piston. Another result is an increased tendency for theremaining gases to spontaneously explode or knock as heat andpressure rise.

Keep in mind, high peak cylinder pressures and tempera-tures resulting from high compression can also produce moreNOx pollutants. Lower compression rarios raise the fuel require-ments at idle because there is more clearance volume in the com-bustion chamber that dilutes the intake charge. And because fuelis still burning longer as the piston descends, lower compressionratios raise the exhaust temperature and increase stress on thecooling system.

Until 1970, high-performance cars often had compressionratios of up to lI or 12 ro one, easily handled with vintage highoctane gasolines readily available in the 98-99 ((R+M)/2) range.By 1972, engines were running compression ratios of 8-8.5:1.In the 1980s and 1990s, compression ratios in computer-con-trolled fuel injected vehicles were again showing up in the9.0-11:l area based on fuel injectiont abiliry ro supporr highercompression ratios without detonation, coupled with the preciseairlfuel control and catalysts required to keep emissions low. Racecar engines rypically run even higher compression rarios. In air-unlimited engines, maximum compression ratios with gasolinerun in the 14-17:1 range.

Ratios above 14:1 demand not only extremely high-octanefuel (which might or might not be gasoline), but experienced rac-ers use tricls like uniform coolant remperature around all cylin-ders, low coolant temperature, and reverse-flow cooling.Extremely high compression ratios also require excellent fuel dis-tribution to all cylinders, rerarded timing under maximum power,very rich mixrures, and probably individual cylinder optimizationof spark timing, airlfuel ratio, and volumetric efficiency.

MAKE SURE YOUR ENGINEIS HEAUTHY AND TUNABLE

Prior to performance tuning, a performance engine must norburn oil, which will tend ro acr as a pro-knock agent. The enginemust have low oil consumption pasr rings, turbo shaft seals, valvestems, and so on. Obviously, the engine should not be leakingwater internally (which would turn oil white), nor should therebe excessive scale in the engine cooling jacket.

The motor itself must be mechanically sound, with ade-quate oil pressure under all circumstances. Most powerful EMSscan monitor oil pressure and sound alarms and take counrer-measures to stop the engine if oil pressure drops dangerously low.There are labs with the abiliry rc analyze used engine oil to checkfor abnormal metal conrent and to analyze the source of abnor-mal metals, which can be very useful in evaluating internalengine health.

If this is a super-dury engine with power-adders, the pistonsshould be thermal-coated, or the engine equipped with oil-squirters, or the rods equipped with an orifice berween the bigend at an angle toward the piston wrist pin designed to providea pressurized cooling spray of oil against the undersides of thepistons to cool it.

The engine managemenr sysrem and sensors musr be work-ing correctly.

The external coolant system must have integriry with theradiator working efficiently. The fans and shroud must be work-ing efficiendy, and if the car is on a stationary chassis dyno, there

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tion timing and injection pulse width to achieve low emissions,best torque (lean or rich), or a specific airlfuel mixrure-or somecombination of all three. Then they road tesr the vehicle and finetune it under actual driving conditions, also fine tuning theenrichmenr maps.

If your ECU has closed-loop capabiliry and is running in aspeed-throttle position range in which closed-loop operation isactivated, your ECU may be able to tell you *h"t th. mixturewould have been if you were running open-loop based on whatamounr of mixture correcrio.t *ir required to achieve astoichiometric airlfuel mixture. You can then make correcrionsto the raw fuel map based on this informarion.

TARGET AIR/FUEL RATIOSGasoline,

.b.ing a srew of hydrocarbons of varying srrucrure, isnot a single homogenous molecule that burns with orygen in aprecisely predictable fashion. Nonetheless, given unlimit"ed timefor combustion and a perfectly mixed batlh of fuel and air, ittakes between 14.6 and r4.7 pounds of air to burn a pound ofgasoline in a reaction that produces 100 percenr -",.i and car-bon dioxide (in this ideal reaction, rhe .ri rog.., in air is purelyalong for the ride). So an airlfuel ratio of t4.z:t is the chemi-cally correcr or sroichiometric rario, sometimes abbreviated bvthe Greek leu.r lambda, as in lambda of 1.0. For example, lamb'-da of 0.9 translates as 0.9 x I4.7, or 13.23 airlfuel ratio.

!n realiry in a high-speed piston engine, there is limitedtime for combustion, the air and Fuel are nolperfectly mixed, andtiny amounts of nitrogen will be burned by hot comLustion tem-peratures. and pressures. And inevitably some gasoline moleculeswill not be burned and some oxygen will not find any fuel toburn. Best power always occurs *hin there is at least a small fuelsurplus above stoichiometric because air (orygen) is the scarcecommodiry.in spark-ignition pisron engines.-The best powerstrateg'y is therefore always to make suri there is enougir fuelavailable so that virtually every molecule of oxygen finJing itsway into the engine will be able to burn fuel. The best economystrategy is to make sure there is a small oxygen surplus so thatevery bit of fuel will get- burned. The best eirissioni strategy iscomplicated by the fact that lowest hydrocarbon (HC) emissionsoccu! as youd expect, with an air surplus, but such lean mixturesproduce hotter combustion, which burns more nitrogen andincreases oxides of nitrogen, known as NOx. The besi overalle,missions straregy, therefore, turns out to be to rarget 1.0 lamb-da, the stoichiomerric ratio, which does not minimize either HCor NOx, but minimizes the sum of both.

Lett first consider rarger airlfuel ratios for sready-stare oper-ation, when an engine is operating continuously at a particularspegd and power ourput and the-various engine fuel, air, andcooling sysrems have reached equilibrium.

Assuming the engine is not knockJimited and therefore doesnot require additional surplus fuel ro cool combustion via heat-of-vaporization effecrs, for best rorque with optimal fuel economy arwide-open throttle, aim for a 12.5:l airlfuel ratio midway berweenlean and mean best torque (12.8-12.2 AFR). If you're willing tosacrifice a little rorque, mixrures as lean as 0.92 iambda (13.5:l)on mild srre€r .rgir., that are not turbocharged will produceexcellen_t peak-power_fuel economy ar the cost o-f about 4 percentpower. Bob Norwood rypicdly saves up a calibration by removing2-3 percent timing and adding the same percenrage oifu.l.

. 9l turb_ocharged or other boosted po*.rpl"r, rs that areknock limited, ar a very minimum yo,r "r. "i-ing for mean besttorque of O.82lambda (12.2 AFR), if not rich beit rorque of 0.glambda (rr.76 AFR. This has the side benefit ar very high speed

136

of increasing. flame speed (which increases all the way to 0.75llTb{"::r.which point a healthy flame front will -ou. throughthis airlfuel mixture at 80 feet per second).

_ Under very high vacuum (deceleration condirions), run15.5:l or 16.0:1 AFR' (1.05-1.09 lambda) or even fuel cut ondeceleration ro prevent lean exhaust sysrem backfiring.

Mild-cammed engines with tuned runners andlimle valveoverlap .operating at full operating remperarures will idle at14.7:r, but such a 1.0 lambda mixture is

^fairly close to produc-

ing misfires, and most engines produce a betier, smoot'her idleand less stalling with richer airlfuel ratios. It is common practiceto set idle lambda at 0.9 (within rhe correction range of th. o*y-gen sensor) and allow the closed loop system to fuil mixruresleaner to stoichiometric at idle and light'cruise under o, sensor.olrrgl: I[ for any reason, the O, ,.rro, fails, the engine willonly idle better. Big-cammed engires will not idle weli at stoi-chiometric mixrures, needing "i l."rt 13.0-r3.5:1 mixtures(0.88-0.92 lambda) to idle as-smoothly as possible, even at fulloperating remperarures.

Subject to engine vE distortions, for best drivabiliry, airlfuelmixtures should smoothly increase fuel in a linear fashlon fromlight cruise at low rpm roward heavier loadings and peak-torquespeeds. Build in smooth increases in mixt-ure as the ..rgirr.increases in speed toward best torque and as loading increases.

The lambda table u99d by the Motec M4g on rh"e MR6 proj_ect in this book as tuned by Bob Norwood sers rarget lambia at0.82 at.one armosphere of boost, decreasing to oI9 lambda atatmospheric pressure, and remaining at 0.9 lambda as manifoldpressure decreases to higher ranges of ta.t'rr'r-.

During transienr operation-when an engine is starting,warming up, accelerating, or decelerating rapidly-ordinary :rLr_get airlfuel mixrures are.no longer applicable; initead, the enginemanagemenr sysrem will apply correcrions to the base airlFuelratios to supply additional fuel.

MANUALLY COMPUTINGTARGET PULSE WIDTHS

But let's lgr giy. up, lett acrually compure some rarget injection

pulse widths. Keep in mind that injectors are nor accurare muchbelow about 1.7 milliseconds (a millisecond is 0.001 of a sec-ond). In addition, som.e injection sysrems will not open the injec-tors more rhan 16 milliseconds under any conditions. Also keepin mind that the amounr of time available for injection is deter-mined by the speed of the engine. At some point, the availabletime for injection and the required puls. *idth crisscross, andthe injectors become sraric, that is, open all the time. \ff/hen inthis realm, you have losr control of fuel flow in relation to enginefuel requiremenr changes, and additional engine speed

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decrease the total fuel injicted and available p.. io*., strok. p.,cylinder. since this would most likely o...rr-urrd.r conditions ofhigh loading at high speed, additional loading could lead to dis-astrously_lean mixrures. check to make sure-that the injectionpulse width is less than 56,000 divided by rpm. For example, at61009 rpm, the available time for injection is 56,000/6,000,which is 9.3 milliseconds, so a specified pulse width greater than9.3 milliseconds would drive the injectori static. MosI oEM fuelinjection sysrems are designed to never require an injector dutycrcle greater than about 80-percent, and research byfuel injec-t.ion expert Russ collins indicates there is good ,..ior for this.According to collins, injectors can begin to hbrill"t. at such durycycles, becoming nonlinear in fuel dilirrery, potentially causinglean-out problems. In practice, I've seen -"ny engines run grearto pulse widths of 100 percenr or above, but ii i, iot" good i"dea.

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MAP (manifold absolute pressure) sensorshould read atmospheric pressure I bar (100 kilo-pascals).- The O, sensor should heat up (you shouldalways use an electrically heated sensor), meaningthe sensor body should feel warm after a littlewhile. If the O, sensor is out of the exhaust sys-tem, you should see rhe tip get red hot shortlyafter you energize it by turning the key to on. Ifyou are using a wideband O, sensor, the laptopshould display a 15.9 airlfuel rario once the wide-band sensor has heated and begun functioning.-The throttle position sensor (TPS) should movefrom 0 to 100 percenr when you open the throt-tle; if not, virtually all EMSs now have a calibra-tion faciliry that allows you to mark the closed andfully open TPS voltages as 0 and 100 percentthrottle.. If the ECU has injector test functions like a MotecM48, test each injector, listening for a rapid click-ing noise from every injector.. Make sure the spark plugs are new, of the rightheat range, and gapped correctly for the engine inits current configuration. Turbo conversionengines usually run a much narrower gap thanstock (that is, 0.029 or less, versus, say,0.044). Cranking an engine when the injectors are wash-ing the cylinder walls with raw fuel while there isno functioning spark to light offthe engine is notsomething you want to happen. If the ECU hasspark test funcrions, pull the high-tension coilplug wire and set the end near a grounded metalsurface of the engine, run the tesr, and watch forrapid sparking. If the engine has direct-fire capa-biliry, you may need to unscrew the spark plugs,

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re-insert each in the coil-on-plug connector, and ground theplugs. In some cases-like the Motec M4-8 with direct-fireexpander module-you may need to redefine the ignirion as sin-gle-coil and then jumper spark to each individual low-voltagecoil wire at the ECU connecror ro watch for a spark at each plug.If there are no spark test ECU rourines, disable the injectors-or make sure there is no fuel pressure-and crank the engine totest the ignition as above.. Check the firing order one more time-for plugs, direct-fireplugs, and injectors if it's SEFI. Make sure you have the officialengine firing order and know how the engine manufacrurer num-bers the cylinders. \With a distributor ignition engine stopped attop dead center at number-one cylinder on the crankshaft tim-ing mark on the compression stroke (both valves closed), makesure the rotor is pointing at the number-one distributor lead andthat the successive distributor wires in the direction of distribu-tor rotation are routed to the correcr cylinders in the firing order.A direct-fire ignition module is normally hardwired with certainpins on the connectors designated first to fire, second to fire, andso forth. Make sure the wiring is right.. Attach a pressure gauge to the fuel rail. Jumper the fuel pumpro prime the system and check for pressure of 3945 psi with noIeaks. De-energize the fuel pump and watch the rail pressureclosely. The fuel pressure regulator should hold steady pressurefor a long time, meaning minutes rather than seconds (the shopmanual for the car may have a design pressure drop per time spec-ification). If pressure drops rapidly (seconds rather than min-utes), the regulator is defective or stuck partly open with dirt or

debris, or one or more injectors are stuck open. Injectors that havesat for a long time in a wrecking yard are particularly susceptibleto sticking. Vhen you're done testing, duct tape the pressuregauge in place on the windshield or other location where it canbe seen after the engine starts and eventually in early test drivingor on the chassis dyno.. If there is any possibiliry one or more injecrors are leaking, itis critical to remoae the spark plugs and injector wiring and crankthe engine ro purge any gasoline from the combustion cham-bers-and then fix the problem by replacing or cleaning theinjector(s). V/hen a piston is stopped very near before top deadcenter and a leaking injector is filling up the combustion cham-ber, the crankshaft will have exrreme leverage against a combus-tion chamber full of gasoline because the crankshaft moves manydegrees of rotation to produce the tiniest piston movemenr. Thistype of Hydro-lock may nnt just stop the engine dead in its trachs; itcan break rods and pistons and smash broken rods though the block.. Attempting to srarr an engine without an rpm or crank triggersignal can be a really bad idea. Disconnect the injector wiring sothe engine will not start (unplug the injector harness or .rnp1.rgall the individual injector connectors), and crank the engine. Ver-ify that the rpm display on the engine data page of the lapropshows a plausible non-zero cranking rpm.. Once you definitely have a correcr rpm, connect a timing lightto the number one cylinder and verify that the spark timing asshown by the timing light matches the laptop's reported timingon the engine data page. If it does not, if the engine uses anadjustable distributor ignition, the distributor might be indexed

Characterlstlc curues.lFl (dfnqmic flow range): Variation ratio futween minimum and maximum injectedfuel quantity at maximum Svo deviation lrom the linearized flow function. Peri6dictimeT = 10 ms.

Duration of injeclion rr

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This chaft effectively illustrates the performance of Bosch fuel injectors at various pulsewidths. For a workable calibration, it is critical to stay within the range of excellentrepeatability for the injectors in use, since the variation ratil between minimum andmaximum iniected goes beyond the critical 5-percent limit at very short and very longpulse widths. Bosch

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F

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point, the EMS will have some means of indicating that it is inclosedJoop

aod.: For example, a readour may begin displayingthe amount of fuel the engine is adding or subiracting to achieu!stoichiometric ratios. Some EMSs havi airlfuel ratio-tables thatallow. a runer to specify nonstoichometric rarger mixtures forclosed-loop operations in various speed and loaJing segments ofthe engine operating range.

are very good, nonetheless. Most ambitiously, some EMSs nowhave an auto-mapping capabiliry that enables the ECU to workwith a wideband sensor to build correcrion tables that trim injec-tion pulse width to achieve the values in a target airlfuel ratiotable (assuming you know the ideal AFRs, whici frequently varyaccording to the engine or engine wpe). Such systems aregoodfor driving around town and allowing the system to tune itself atlight and midrange power sertings, but I woul d not trust such asystem

_ro.find optimal AFRs for high-boost, high-power opera-tiol^s.

You'1. going ro wanr to sneak up on dangeioui high-powerairlfuel ratios manuallv.

VE TABLESvE tables are useful for engines that are not equipped with massairflow sensors, and which rely on manifold abrtlur. pressureand engine speed to estimate engine airflow vE tables co.r.ct forthe fact that only engines with a perfectly flat torque curve havea perfecdy_ linear relationship bimeen manifold pressure andengine airflow across the rpm range.

vE tables add a kind of elegance to engine managemenr sys-tem design that does not exist on EMSs that simply liok up fuelinjectio_n pulse width or timing advance in a tatle of rpm andmanifold.pressure cells. Altho ugh any speed-densiry table of tim-

lng or pulse width data is gging to correlare roughiy with enginevE, a pure vE table describing the engine's breathing efficie"ncyacross the range of operation is uncomplicated bylompetingpurposes such as the desire to optimize some poitions ir ,nIoperating range for efficien cy or low emissions and others formaximum power or the need to warp fuel delivery or timing tocool combustion or fight detonationln certain areas of the map.Any of rhese, for example, could cause a speed-densiry-pulsewidth table to depart from perfectly describing vE. An'enginemanagemenr sysrem in possession of reliable engine vE infor-mation in effect knows actual mass airflow into ihe engine andcan use rhis information in a variery of ways to optimiz"e enginemanagement in various rypes of self-learning and targeted opti-mization strategies.

. . The engine management systemt volumetric efficiency

table is a critical chart of numbers that represents the .ngin.tbreath.ing efficiency across the range of engine speeds and ioad-ing. The vE table e^ssentially tells the engine -.rr"g.-.nr sysremwhat percenrage of the engine's displaciment wi[ make it intothe cylinders at each and every porribl. combination of rpm andmanifold pressure. Manifold p..rr.rr. is itself a function ofengine breathing,capabilities, throtde angle, and the operatingstatus of installed power-adders. vE is dependenr on tire basilengine design, including head design, camshaft profile, power_adders, and engine speed.

. Engine VE rypically varies somewhar from 100 percent in a

positive or negative.direcrion (usually negative), depending onwhat the engine is doing and how it'is designed. once the sys-tem knows how much air there is in the .yli.rd.rr, .o-p,r,i.rghow much fuel the engine needs is simple.

There are an infinite number of possible engine speed and

F"{tlg numbers, so various engine management systems settlefor vE tables of a fixed number oTcells (s,rc"h as t6xi6 or 20x40),with points falling in between the resolution of the table calcu-lated as a weighted average of the closest defined cells (sometimesreferred to as breakpoints). If an engine is breathing an amounrof air equal to.100 percent of its displacement, the vi, is 100 per-cent. Depending on the table, this number may be representedas a_ percencage (1.00), or a plus-or-minus offset (0.00), or evenas the fuel injection pulse width (for a certain size injector) that

The trick with closed-loop operations is to tune the raw fuelcurve of the engine so the engine runs great under all circum-stances even if closed loop is turned off. Under no circumsrancesshould uncorrecred mixtures ever be leaner than stoichiometric.If the o.r.sensor fails, the system will default into open-loop

l_odg, which you always wanr ro be perfect or on th. ii.h rid..The base fuel maps should be construited so the closed-loop sys-tem. is {ways either idle or pullingfuel, never working rc aid furlto the base map. Keep in mind that the o, sensor ir ,ro, in thecombustion chamber but rather is located downstream some-where in the header(s)^or exhausr system, and there is a varyingdegree of.lag. in the O, sensor reading, depending on enginispegd and exhaust veloiiry. A properly calibrated Etrrts shJutd

ftil safe, which, in this ."r., o'.an s fail rich.Typically, OEM EMSclosed-loop sysrems are clamped to limit the'maximum fuel trimto a.rather small percenrage; if the sysrem is adding or subtract-ing huge amounrs of fuel, somerhing is probably ieally wrong.Later on, we will talk about using exhaust gas remper"r,rr. ,."J-ings to tune safely at high power levels, but even gcrr have lagtime, and combustion remperarures are rypically much hocter inthe chambers than even a short distance downstream in theexhaust. Bottom line, the base fuel map should err on the richside, but never by more than about 5 percenr.

Vhether or nor you plan ro run Closed loop once the EMSis optimized, you ne_ed wideband capabiliry to dial it in. Keep inmind, narrowband o, sensors are not capable of providing accu-rate readings very far from 14.68:1, that is, below 14 or-muchabove 15 (though they will immediately and clearly warn of atoo-lean condition without the driver having to rhink throughwhat it means). The automatic starr-up mapping faciliry mayproduce a map that will start and op.tat. ttre "ehicle wirh decentdrivabiliry but airlfuel ratios and timing will almost definitelynot be. optimal. Tlr.t*t:: you're going-to need wideband O,capabiliry to find the "free"

po*.. "nd efficiency in your engi.relIt is a fact of life that virtually all pro runers *oik *ith wide6andO, sensor data in all tuning operations, and many Dynojet chas-sis dynos are now equipped with wideband capabilities'that logairlfuel ratio information and graph it along with powe, ".rdtorque. Alternately, some of the newer EMS; ha.'. a wideband

lption, which may allow the EMS to read and log data from afive-wire o, sensor (which rypically costs hundreis of dollars),though nor necessarily to use for closed-loop feedback opera-tions. Narrowband o, senso-rs deliver a voltagi becween tt."rly 0and nearly I volt (a few are frequency-based). \fideband sensorstypically deliver a 0-5 volt signal that is not comp^tible. Morerarely, some EMS sysrems can now work with a conditioningprocessor that converts wideband o, data to the 0-l volt signJneeded for actual closed-loop trim"operations (an .*r-pi-. i,Links UEGolink). Another oprion is employing a standalonewideband airlfuel-ratio meter that is not p"rt oirhe EMS butinstead indicates the airlfuel ratio in real time on a digital displayor analog gauge needle. \wideband sensing of any.,"ii.ry greatlyincreases rhe accuracy of tuning under all conditio.rr, "rd ii accu-rate in detecting airlfuel rarios from about l0:l all the way roabove 16:1. The trouble is, standalone AFR merers .".rnoi b.correlated with datalogging information from the EMS, but they

140

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One good way ro build a VEtable is to use the O, sensor ro tar-get identical airlfue-l ratios in allspeed-loading points, which ismade easier by the fact that manyEMSs now have a target AFRtable. If you have a wideband O,sensor, you can set all cells in thetarget lambda (airlfuel ratio) tableto 12.8:1, which should be safelyrich enough to set VE in cells ref-erencing high power and torquesettings on all but the most radicalhigh-boost powerplants (but notso rich as to harm idle qualiry orproduce surging at light cruise). Ifyou are using a narrowband sensor,it will not have the authoricy toaccurately distinguish airlfuelratios this rich. Some people sug-gest that on a normally aspiratedengine without too much com-pression and power, you can trysetting up rarger ratios of 13.2(0.89 lambda) in all cells and runthe process, but standard O., sen-sors are not particularly accur-ate inthis range so far away from lamb-da 1.0. Under no circumstancesshould you atrempr ro ser VE atthe more dangerous high-boost VEcells with just narrowband data.

Turn off the parameter thatdeactivates closed-loop aurocorrection in conjunction with thetarget AFR table, but make sure theO, sensor readour stays active.

It is a good idea ro ger someidea of which cells are being usedby the EMS to fuel the engine by using a cell highlight if thereis one to mark the speed-densiry cells as you operare the engine.This will enable you ro concentrare on correcting the appropri-ate cells first.

'Working cell by cell on the road with a runer riding shot-

gun with the laptop and a driver with one foot on the gas andone foot on the brake (hopefully on a deserred country road ortest track) working to achieve rarger rpm and engine loadings (or,even better, using a load-holding engine- or chassis-dyno), adjustas many cells as you can reach in the VE table to bring the actu-al values in the rarger airlfuel table back to the identical rargerI2.8:l (or 13.2) airlfuel ratio. The trick is to work methodical-ly, staying away from sudden acceleration, stabilizing the vehicleat the various breakpoints before moving to the next.

If you have a fresh, accurate wideband sensor, a tankful ofracing gasoline and a known-conservarive srartup map, it may befeasible to turn on auro-correct closed-loop operation and drivearound, noting the amount of fuel the system is having to sub-tract or add (hopefully not much) to achieve the target rarios, fix-ing the VE table as you go.

Keep in mind that the trick is changing not just one cell,but smoothing in the surrounding cells to form a smooth slopeor graph. If you do not change surrounding cells along with thetarget cell, you will probably not get the full magnitude of

changes reflected in actual injection pulse width, since the EMSwill average our sharp peaks and valleys. So change one break-point a modest amounr, then switch over ro graph mode and pullthe surrounding cells up or down as required to make a smoothslope. If this is not enough, do another iteration. \What wlll notwork well is to yank one cell to ridiculous heights before gettingaround to other nearby cells.

On some sysrems you can datalog the actual airlfuel ratiosas you drive the vehicle through the range of speeds and loading,and have the system tell you the pulse width required to achieveentries in the rarger ratio table-or even do the actual pulsewidth compensarion. Using datalogging this way can be effiiientbecause a relatively quick rest run can be made to encounterman! cells in the airlfuel or VE table, which can then be fixedfollowing the run, offline if you like. If is also safer, because abri.ef foray into each cell is enough, with no requirement to lingerin high-power cells while you make sense of what is going o.r *dmodify the VE or injection pulse width. However yor't do it, workyour way through the table, adjusting VE to bring the actual AFRvalues in the fuel table back to 12.8:1 (or 13.2:l if narrowband).Beware of the most dangerous high-boost cells on a 2- or 3-barboosted engine.

Note: Some highly sophisticated EMSs do not use a specialVE table. Instead, they use VE-type tables of pulse width and

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With sequential fuel iniection you will probably have the option to define injection phasing, in particula4the engine position in the 720-degree four-cycle by which injection must conclude (or start). tnjectiontiming can typically be adjusted at various rpm points and optionally at various efficiency points. Adjustingthe iniection timing allows the fuelto be injected atthe optimum point in the engine cycle so the fuet isused most efficiently. Engine powe7 emissions, economy, and idle stability may be optinized by adjustingthe injection tining.

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\[hen youve got the zero-load cells set, smooth any jaggedtransition to adjoining cells in the fuel table, find a helper, andgo for a drive on a safe deserted road or test track. Tiy to drivethe car at a steady state at as many speed-loading cells as possi-ble. It will help the driver if the laptop can be setup with the dis-play magnified so itt easy to read from a distance and positionedso that the driver can use the screen to home in and make a cer-tain cell current-and then back off while the runer riding shot-gun modifies this and surrounding cells. The targer AFR for lightcruising is 14.5-14.9 or 0.99-1.01 lambda, though you may beable to successfully tune an engine with very mild camming forgood fuel economy at light loading with airlfuel mixturesapproaching 16:1.

Again, a mixture trim module can be very useful for instant-ly testing percentages of enrichment or enleanment. You or thedriver can just turn the trim pot(s) to optimize performance orhome in on a certain AFR. Then you can note the actual pulsewidth fueling the car and the actual speed-loading cell, or norethe percentage of change being made, and then back off andmake the changes to the targer and nearby cells.

At medium engine loading, you'll need to rarger richer mix-tures in the neighborhood of 13:1.

As the midrange srarrs ro get fleshed out, bring up thegraphing function and work ahead on the graph to keep higherthrottle settings in line with how the midrange is shaping out andconsistently richer than what is proving to work in the midrange.Again, the trick is to make brief forays inro high-loading condi-tions, watching the AFR and the rate of acceleration and dri-vabiliry, fleshing out the active cells and cells in adjacent areas.Some people find it much easier ro rune tables in graphical for-mat, using the mouse and arrow keys. Others find it easier to editnumbers in the table, perhaps flipping back and forth berweentabular and graphical format (there will usually be a hot key forthis purpose). However you do it, getting an occasional look ata 3-D graph of the fuel or VE table is very valuable, because you'llbegin to get a sense of the overall surface of the map, and you'llalso be able to see any anomalies in the surface that probablydon't belong there. You'll probably find that only a relativelysmall portion of the fuel map is used much and that you have rowork to get the engine running very far off the beaten path, soto speak. If you started with a plausible srarrup map and havealready mapped our a main VE table, whar we're doing here isjust fine tuning, but always sray on the rich side.

For normally aspirated srreer vehicles or boosted engines rhatare not severely knock-limited, mean best torque should fall in the12.4:l range at the highest power settings, but boosted enginesmay require more fuel cooling to fight knock and meltdown. If,as recommended, you are running redly high-octane unleadedracing gasoline to minimize the effect of lean mixrure mistakes,runaway boost, or poor tuning technique, knock should not be aproblem at this time, particularly with a conservarive timing map,and, preferably, a good EMS knock-sensing and retard EMS strat-egy or possibly an add-on device like the J&S Safeguard (whichwill actually retard individual cylinders only to the degree need-ed to stop knocking in that qtlindzr). At some point, you will haveto turn off the knock-retard program in order to optimize basicsafe timing and safe-up timing, fuel, and boost to work with thegasoline octane you'll be running, but nor quite yet.

Bob Norwood points out that super-dury engines alwaysmake the most power as you lean them out right before they burndown. Really experienced, brave tuners like Norwood workingcarefully for every last horsepower on a race car will somerimesrun high-power AFRs leaner than 12.4:1 (say as much as 13:1),

but such mixtures are more dangerous in really high-outputengines, and-as Norwood, who has set a variery of land-speedrecords at the mile-high Bonneville Salt Flats, can testify-suchtuning makes an engine more sensitive to variations in altitudeand relative humidiry. An engine is producing its most powerfulputts at peak-torque rpm, ingesting the most air per powerstroke, producing the highest cylinder pressures. The higherstress of increased peak-horsepower rpm will definitely producegreater stress on mechanical parts like connecting rods, and peal<horsepower will result in more thermal loading to the coolingsystem and so forth (which can increase the tendency for deto-nation). But peak rorque makes the most cylinder pressure, andit requires slightly richer mixrures than peak power. Many runersrecommend optimizing the high-power calibration by tuningfrom a known over-rich setting and then carefully leaning themixture until torque falls off slightly, then moving in the richdirection until you achieve peak torque.

If you develop the fuel map on a chassis or engine dyno, youwill almost definitely need to lean out the map for best per-formance in the real world of either competition or srreer per-formance. For one thing, dynos cannot accurately crearereal-world conditions like underhood airflow at speed or ram-aireffects. \{/hatt more, dynos capable of holding the engine indef-initely at a certain speed and loading provide extremely highthermal loading that demands safe-rich mixtures that may beinappropriate for achieving optimal performance on rhe streetunder less severe conditions. Also, EMS fueling strategies rypi-cally involve averaging in nearby cells to a fueling calculation, sorich mixtures required at cells that are essentially unreachableexcept on the dyno can adversely affect the AFR on the srreet atnearby areas of the fuel map that are reachable.

High-power tuning is when exhaust gas remperarure (EGT)data can be useful ro warn you of danger before it is too late. Youcan take it to the bank that a piston engine will make peak powerat somewhere between 11.8 and 13.0:1 AFR. However, the EGTat the peak power AFR is less predictable and depends on manyfactors, including ignition timing, cams, pisrons, headers, erc.EGT at peak power might be anything berween, say, 1,250 and1,800 degrees, or even a bit hotter. Typical peak EGT on a per-formance automotive srreer engine would be more likely in therange of 1,350-1,550 degrees. Peak EGT rypically occurs atabout 75 degrees Fahrenheit lean of besr power, and temperaturefalls off from there in both the lean and rich directions.

EGT is commonly used on piston-engine aircraft runningessentially at steady srare ro lean the airlfuel ratio for peak poweror best economy, and the procedure is always specific ro a par-ticular engine rype in a particular aircraft. But pilots rypicallybegin leaning from a particular rich mixture (based on a partic-ular flow in gallons per hour on the fuel flow meter) used to pro-vide a high-power climb out. From there they gradually lean themixture for best economy in cruise flight manually until theEGT reaches a peak temperarure (rypically measured at the tur-bine inlet), and then continue leaning until EGT is 50 degreescooler than peak.

Continuous EGT above 1,550 degrees would be a cause forconcern on many engines. If you make a nore of the EGT on anengine working at a known optimal peak-power AFR, then cer-tainly a rapidly rising EGT moving out of the expected rangecould warn you that something is dangerously wrong in time totake countermeasures. As an example, detonation will rapidlyincrease combustion remperature and EGT, but this wouldn'raffect the exhaust gas oxygen contenr as seen on a wideband AFRsensor. A pyrometer has the additional advantage that it is not

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with careful forays into boosted territory, using a wideband O,senso! and preferably a knock sensor to help prorecr the enginefrom knock or lean-mixture damage.

OPTIMIZING SPARK ADVANCEAs EMS-builder Electromotive says in the TEC3 user manual,"Perhaps

the most important step in tuning an engine is estab-lishing the required ignition advance. An engine with too muchtiming will detonate, regardless of how much fuel is rhrown atit. An engine with too little timing will perform poorly and over-heat the exhaust in short order." Late ignition timing can makean engine run roughly, and it will definitely increase the exhaustgas temperature (since the mixture conrinues burning later in thecombustion cycle). If the exhaust headers are glowing, you knowthere is too little timing; if the engine is knocking, timing latemay be too advanced.

Optimal spark timing varies, with the overall goal being tolight off the charge mixture in time so that peak combustionpressure occurs when the piston is at l5 degrees after top deadcenter on the power stroke. A critical overarching requirement,however, is also to avoid engine damage by delaying light-off tothe degree required to avoid having unburned portions of thecharge explode as combustion pressure and heat build during theburn (as the piston may still be compressing rhe mixture). Theoptimal amount of timing advance varies inversely with volu-metric efficiency because denser mixtures burn faster and requireless lead time to achieve the l5-degree peak.

Therefore, engines need more advance at low-load, narrowthrottle settings when VE is poor. At rhe same time, when theengine is running at high speed, a combustion evenr of fixedlength in time consumes more degrees of crankshaft rotarion,requiring more timing advance. Combustion speed and crankdegrees per millisecond are thus independent variables. VE ispoor at idle, but engine speed is slow, so 8-20 degrees of timingrypically works well. As the crank quickly accelerates off-idle, ahuge infusion of spark advance produces the best torque andresponsiveness, with some wild-cammed engines with very poorlow-end VE requiring as much as 28 degrees total advance.Engines cranking to starr turning 200-300 rpm require moder-ate spark advance with nearly as much timing as idle.

As the throttle opens and the engine speeds up toward peaktorque-peak VE, combustion speeds up along with VE and thusrequires less spark advance. Peak timing usually occurs by 3,000rpm on most engines. On the other hand, high engine speeds atvery light loading require huge amounts of advance-as much as40 degrees or so. If the engine is turbocharged, the onser of boostincreases the effective compression ratio, and combustion speedsup dramatically, requiring less timing, and simultaneouslyincreases the risk of detonation. Maximum timing at 1.0-barboost is rypically in the range of 23 degrees at any engine speed,and 2.0-bar boost might only want 22 or even 2l degrees of tim-ing advance. All things being equal, bigger engines need moretiming advance because it takes the flame longer to burn its wayacross a large bore than a smaller one. Engines with small com-bustion chambers need less timing (opposite reason), and engineswith pop-up pistons or other irregularities that slow down flametravel in the combustion chamber need more timing.

Spark advance maps plot spark timing as a function ofengine rpm and engine loading (normally manifold pressure ormass airflow). Unlike convenrional distributors with mechanicalsprings and advance weights and vacuum-advance diaphragms,which are mechanical devices incapable of providing timingadvance that varies excepr as a smooth curve or straight line,

computer-controlled timing can dance all over the place if thattwhatt optimal. It can certainly approximate a complex 3-D sur-face with various peaks and valleys if thatt what produces thebest performance on a complex engine with, say, muitiple power-adders and numerous accessories and so on.

Conventional distriburors smoothly increase timing withengine speed. Though rwo springs of varying strength may beused to bring in some timing advance quickly with initial speedincreases, then bring in more as the rotating weights overcomethe force of the second spring. High vacuum at light loading wasused to add timing. It would be a simple marrer for EMS design-ers to provide rwo separate timing tables-one for rpm advance,a second for load retard-but one additive timing table makes itsimpler to calibrate, and, besides, the real trick is an exhaustivesearch for power on a dyno while the engine is running. Vhocares why you need more or less timing?

A modern EMS with knock-sensor/spark-rerard logicshould be calibrared with enough timing to provide peak rorqueacross the board using design-octane fuel, but may rely on knock-sensor-feedback logic to pull timing ro prorecr the engine fromoccasional light knock in case of a poor tank of fuel or if theengine is unusually hot (or if anything else unusual is happeningthat makes the engine especially knock prone). Howevei runersshould work rigorously to calibrate timing conservarively enoughthat the knock sensor normally neuerbecoms5 x6siys-by elimi-nating excessive timing advance in any area of the timing mapwhere the knock sensor sounds off in order to clamp maximumtiming within a normally safe range. Setting maximum timingby advancing timing as far as possible to the ragged edge olknock-sensor activation will probably yield best fuel economythough nor necessarily best torque. (lt was once common to settiming on older carbureted engines with distributor-points igni-tion by advancing the distributor in actual road testing to theragged edge of incipient spark knock.) Over-advanced timingmay also cause the engine ro surge at cruise.

Aftermarket mechanical hot rod valvetrain parts may gen-erate enough background noise to falsely trigger the knock sen-sor. If this is the case, keep in mind that any knock sensor shouldideally be selected to match the frequency of the detonationcharacteristics of a particular engine, which might not be trueof a particular generic aftermarket sensor. There are a lot ofknock sensors, and anorher one tailored for a different frequen-cy might work betrer. For example, an original-equipmenr sen-sor selected specifically for your engine-or, if your engine hasbeen modified and you are getting false positives, perhaps specif-ically a non-OEM sensor). Normally, a small four-cylinderengine should have a knock sensor designed for a small Four-banger and so on.

A possible alternative to changing sensors would be to exper-iment with changing the location of the sensor in the block orhead(s) or even mounting it with Teflon rape or other insulatingmaterial around the threads to decrease sensitiviry. Some after-market knock-sensor control systems have the abiliry ro tune orcondition the EMS or knock-controller response to various typesof knock-sensor signals ro narrow the response to what is actual-ly detonation as opposed to engine noise. However, if the engineis simply too noisy for a knock sensor and you have the bucksand like experimenting, you could install in-cylinder pressuretransducers, some of which are bundled with special spark plugsto detect knock and provide a readout of torque or brake meaneffective pressure (BMEP). Measuting cylinder pressure is actu-ally much more accurate than listening for knock-like vibrationsusing a knock sensor.

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. Temperature-based limitations to maximum boost to pre-vent engine damage while the oil is still thick.. One-second temperature-based start enrichment. One-second constant enrichment. Fixed one-second starting pulse width

Many cold-running tables are designed as a final percentagemodification to the ordinary fuel and timing calculations, whichis why it is essential to get the EMS working really well at nor-mal temperature before you mess with the cold tables. However,once the engine is running great under ordinary conditions, it isreally simple to wait until the engine is fully cold, bring up thewarm-up map as a graph, start the engine, and adjust the mapup or down at the current temperature (an arrow or somethingsimilar will highlight the current coolant temperarure) until theengine runs smoothest, then repeat the process as the enginewarms up and the temperature increases.

A cranking engine will rypically be affected by both warm-up and cranking enrichment, and initially it can be hard to tellif you need more cranking fuel and less warm-up or the reverse.Immediately after starting, it can be hard to tell if you need moreor less after-start enrichment or if you should be modifring themain warm-up map. One clue would be to watch what happenswhen the cranking and after-start enrichments disappear. Doesoptimal warm-up enrichment suddenly decrease or increase?

A rypical engine might need 10 to 15 percenr enrichmentimmediately after a cold start in order to achieve a l2-12.5:IAFR on a mild street engine (perhaps as low as I 1:1 on more rad-ical engines), and this requirement will decline to nothing some-where at or above an engine remperarure of I40 to 180 degreesFahrenheit, with more enrichment required in really cold cli-mates. Vhen cranking in really cold winter weather, the enginemay need grossly rich primine AFRs in the neighborhood of 4:1to start the engine fast. Beware a sudden cold snap or, say, a tripto a mountain ski area from palm-lined Los Angeles when youhave never had a chance tune below 50 or 60 degrees. You mightbe unable to start the engine without a laptop. Though in a pinchyou could probably start the engine by spraying starting erher,carb cleaner, \7D-40 (or perhaps even gasoline, somehow, ifyou're ingenious) into the manifold plenum through anunplugged vacuum reference line.

The engine must be stone cold to set cold cranking andwarm-up enrichment accurately, which means you will want toattack the problem first thing in the morning after the engine hascold-soaked over night. You really want the coolant temperatureat 70 degrees or lower to begin the process.

It may work best to adjust the throttle plate to a reasonablesetting for cold-running idle and later work ro program the IACfor an ideal cold idle speed after the mixture is right. As always,a wideband O, readout may be useful, though the goal of cold-running enrichment is purely to eliminate stalling and improvedrivabiliry you never need more fuel than what is obviouslyneeded for this purpose. A mixture-trim module could be veryuseful when you are working to optimize the AFR for fastestcold idle.

Start the engine and try dialing in greater or lesser coldenrichment percentages until the engine runs best. As always,modest trim changes are best, since a few percent can make alarge difierence in how the engine runs. The EMS will not havean infinite number of temperature cells. Stay on top of it as theengine warms up and moves to a higher temperature range. Youmay see the engine change speed or change audibly when thee ngine moves to a new discrete segment of the warm-up map.

If an engine with reasonable timing will not srart, ir is eitherbecause there is too little enrichment or because the engine isflooded. A flooded engine will rypically smell strongly of gaso-line. To confirm flooding, you can remove the plugs to check ifthey are wet. If the engine will not start when cold and the plugsare not flooded, there is probably not enough fuel.

AGCELERATION ENRICHMENTSome people compare acceleration enrichment on a porr-EFIsystem to the accelerator pump rypically used to squirt raw fueldown the throat of a traditional Holley four-barrel carb when thethrottle rotated. Though EFI rypically needs less accelerationenrichment than a carb because bogs in air velociry that affect acarbt mechanical abiliry to get fuel in air have no effect on EFI.The accelerator pump was something of a Band-Aid heavilyrelated to air velocity and problems with the fuel equilibrium ina wet airlfuel manifold.

Acceleration enrichment (or enleanment) is critical roresponsive drivabiliry and all EMSs will arrive with plausibledefault data designed in. However, there is almost always roomfor improvement, and sophisticated EMSs offer a large and pow-erful set of acceleration enrichment functions to make sure thereis never a problem with transitional enrichment that cannot behandled in some way.

Thansitional enrichment is the final major sysrem to opti-mize and should be attacked when everything else is in goodshape. If you mess with it before the main fuel tables are right,it could confuse the process of calibrating normal operation.Tlansient enrichment is normally used to keep the engine fromstumbling when you suddenly open the throttle (not normally aproblem on port-EFI systems), and to make sure that the engineis as responsive as possible when you suddenly stab the throttle.

Most EFI systems can now provide acceleration enrichmentbased on increases in throttle angle and/or sudden changes inmanifold pressure. Providing enrichment based on falling MAPis somewhat analogous to the way a Holley carb used a powervalve to fix a lean hesitation and surge when rhere was a largedrop in vacuum (for example, if you started up a sreep hill) priorto a corresponding increase in throttle angle.

The main components to acceleration enrichment are basi-cally attack (sensitiviry) and sustain, and there the EMS may pro-vide separate rules for enrichment at low rpm (when the vehiclecan probably accelerare very hard) and at higher rpm. Attack isthe percentage of enrichment that should be commanded whilethe throttle angle is increasing at or above a threshold rate. Sus-tain specifies how fast to phase out the enrichment. Electromo-tive points out that the rypical duration of required rransientenrichment on acceleration is around one second.

There is no diagnostic tool that will tell you when the accelis right. Inertial chassis dynos like the Dynojet will measureincreases in torque and power as you roll on the throttle. But theDynojet is not very good at dealing with partial throttle situationsbecause it is difficult to distinguish the human factor in bangingdown the gas a certain amounr, versus how the engine respondswhen you bang it down at a certain rate (one imagines robotsincreasing the throttle an exact amount at an exact rate ofincrease).

However, if you have the time and the dyno, the Dynojetcould possibly help you optimize accel enrichment. In any case,sooner or later, you'll need to hit the road, and the trick here isbasically a lot of patience and intuition, and plenry of trial anderror with a laptop attached and available when you discover aproblem. If you are working on the dyno, it may be easier ro see

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tuners like Norwood can build a pretty good scratch calibrationin a few hours on a dyno, they are also likely to spend signifi-cant time test driving the vehicle with a laptop connected to fixproblems, and they may well return to the shop for more dynotime where optimal performance is critical.

Beyond this, they will also need some cool mornings tooptimize the warm-up maps, and they cannot really know if thewinter-weather calibration is truly right until the really coldweather rolls around. Automakers often spend months or evenyears building the perfect calibration that will be mass producedin hundreds or thousands of vehicles. Tuners and their cus-tomers certainly cannot afford to do this. But an individual hotrodder or club racer who does it for fun can take the time to doit right and stay with it until the calibration is really right. If youare patient and scientific and willing to buy or rent diagnosticequipment, if you keep notes of what you have tried and theresults and attack one variable at a time, if you take pride in yourwork, you will home in on a great calibration.

ADVANCED STUFF: INDIVIDUALCYLINDER INJECTOR AND TIMING TRIM

Some engine management systems provide a set of advanced fea-tures that can be useful if you want to optimize engine per-formance under all circumstances. Examples of such featuresinclude the following:. Individual-cylinder fuel trim. Individual-cylinder timing advance trim. End-of-injection phasing (crank angle). VE correction to target air/fuel ratios. Engine coolant temperature VE correction. VE correction coefficient versus estimated intake port tem-perature (density deueases with temperature, but hotter airpumps more easily). Knock-sensor functions (threshold definition, rate of knock-

induced advance retard, rate of advance increase on recovery,maximum retard allowed)

Many of these advanced features are useful only within thelab-type environment of an engine dynamometer equipped withsubstantial diagnostic equipment, or on an exhaustively instru-mented race-rype vehicle with a large datalogging capability. Asan example, individual-cylinder trims can be useful to correct forminor variations berween cylinders in volumetric efficiency, ther-mal loading, and so forth. Even on a well-designed and builtengine, some cylinders may run a little hotter or colder, somecylinders may have slightly more tendency to knock, some cylin-ders may have slightly different intake or exhaust runners that canaffect VE under certain circumstances.

In the days of high-output single-carbureted V-8 engineswith points ignitions, fuel distribution could be terrible and cer-tain cylinders almost always had better cooling than others.Unfortunately, there was no choice but to tune the carb richenough to avoid dangerous mixtures and detonation in the lean-est cylinders and to set timing to avoid detonation in the hottestcylinders. Modern port-EFI engines obviously avoid most prob-lems with mixture distribution, though testing and matchinginjectors for perfect flow definitely makes sense if you are gearingup to optimize individual-cylinder performance. There can alsobe minor differences in cooling and VE that are not practical toeliminate, but which can at least be optimized: an eight-cylinderengine is actually a gang of eight single-cylinder engines.

To make any sense, individual-cylinder tuning requires indi-vidual-cylinder instrumentation. Accurate, fresh EGT probes oneach cylinder are critical. \Wideband O, probes cost as much as$ 1,000 each, so itt clearly not practical for most people to runindividual-cylinder AFR probes. In-cylinder pressure transducersare extremely effectle in measuring the effect of individual-cylin-der tuning strategies, and there are spark plugs with built-in pres-sure probes. You clearly need the ability to measure small changes

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torque where tuned intake and exhaust sysrems are most effi-cient. On racing engines, where charge densiry of atomizationcan be improved by taking advantage of the intercooling highheat of vaporization by injecting farther upsrream, spraying atthe wrong time can result in fuel being blown back out the stacksor directly through into the exhaust sysrem on valve overlap, pro-ducing distribution problems or wasred fuel and high emissibns.

In order to eliminate standoff distribution problems, it iscritical to inject fuel when the intake valve is open so that fueldoes not hit the closed valve and bounce back along with thedecelerating, bouncing air column. On a plenum-siack turboengine with compressed air entry ar one end, depending on theresonant frequency, standoff fuel can be blown to the stacks far-thest away. Individual cylinder pulse width or injection-phasingadjustment can correct for distribution problems related to res-onant differences in the airflow to each cylinder (particularlywhen the injectors are open a lot)-realizing as much as 8 per-cent.more power. According to \(/estern, a 60 to Z0 percent injec-tor duty cycle usually makes best power. Larger injectors get allfuel in while the valve is open, but the tradeoffwith short injec-tion time is poorer vaporization and cooling.'Western

says you always see power increases over batch fireinjection at mid- to high-range rorque; a six-cylinder rruck thattested at 280 horsepower with batch-fire injection will pick up20 ft-lbs of torque at peak rorque and 12 to 16 horsepower atpeak power with sequential injection. A 200-hor..po*i. racingengine might make up to 5 percenr more horsepower due to gen-eral phasing correcrness. Individual spark trim is usually associ-ated with detonation-limited engines. Retarding timing on justthe offending cylinders (rypically 2 to 3 degrees) lowers peakcombustion remperature and cylinder pressure, helping fight det-onation. Vhere exhaust gas remperarures are roo high on turbomotors, tuners may run a little extra fuel or spark timing in thecylinder causing problems-or increase overall compressionratios. Raising compression is preferable to advanced timing. Theincreased expansion ratio of gases from a smaller combustionchamber results in greater loss of temperarure than retarding tim-ing, and the increased compression ratios improve peak and aver-age cylinder pressures instead of simply peak cylinder pressures.

AIR/FUEL OPTIMIZATION PROCEDURESON A PISTON-ENGINE AIRCRAFT

Modern turbocharged aviation piston engines, which rypicallyrun at 75 percent power settings more or less constantly, andwhich must run at high takeoff power settings for long minutesor tens of minutes at a time on takeoff and climb-out, rypicallyleave airports full-rich, which would rypically be 100 to 150

degrees rich of peak EGT (75 degrees rich of peak rypicallymakes maximum power). The EGT gauge is critical to the lean-ing procedure used to arrive at an optimal power and AFR set-ting for cruise flight and illustrates something about the meaningof safe. Obviously, ifyou burn down an aviation engine, you can-not simply coasr over to the side of the road.

Engines with poor mixture distribution are sensitive toleaner mixrures and will run roughly on the lean side of peakEGT. Many aviation engines, which typically still usecarburetion of constant mechanical fuel injection, vary in AFRby 8 to 12 percent among the various cylinders But on well-balanced aviation engines, an excellent procedure for arrivingat mixtures producing high levels of safe power is to begin theleaning procedure with the engine running more thin 100degrees- rich of peak EGT, with manifold pressure slightlydown from full throttle. The pilot or flight engineer thencarefully leans the turbocharged engine Lntil EGT peaks(which would often be in the neighborhood of 1,500 degreesFahrenheit. At this point, the procedure is ro continue leaninguntil EGT cools to 40 to 60 degrees below peak EGT (thiswould typically be only 15 to 30 degrees lean of peak on anormally aspirated engine).

Consulting an aviation EGT chart for a common pistonengine, we see that EGT falls off fairly evenly on both the richand lean side of peak EGT, whereas cylinder head temperarureson an air-cooled engine were 35 to 40 degrees cooler on the leanside of peak EGT, and fuel flow was markedly lower.

However, power is down on the lean side, right? \fell, yes,assuming you continue to run the same manifold pressure. If aplane requires more power in cruise flight, in this piocedure, thepilot increases the throttle to raise manifold pi.rr.rr. to therequired power setting with a few more inches of manifold pres-sure. High-performance aircraft engines rypically have consranr-speed propellers that use hydraulics to vary the angle of attack of

the grop to maintain a particular manually adjusted prop speed\flithin a particular envelope, such engines will not inciease inspeed with more throttle.

This procedure requires good mixture distribution, or rheengine will run a little rough due to uneven mixture distribution.But the implication of this procedure is interesting for EFI auto-motive engines with excellenr mixture distribution, running highoctane gasoline. Leaner mixrures srress the cooling system leis,and the EGT is not highen Power might be down a mite, butmore boost handles that, at less fuel flow. Something to thinkabout, because a piston aviation engine pulling against a con-stant-speed prop is a lot like a piston automotive engine pullingagainst a steady-load engine dynamometer.