Tune To Win (Part 2)

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Tune To Win (Part 2)

Postby dan_b » Wed Sep 20, 2006 4:44 pm

Tune to Win :D

In our previous installments of this series, we have been talking about many of the basic and not-so-basic stuff that you can do to get more power out of the propulsion unit--otherwise known as the engine--under your hood. Until now, we have covered about all that can be done without spending super-serious bucks or pulling the engine out of the car and tearing it apart. If you have gotten this far in your path to total dominance, you have gone about as far as most gearheads ever go. Venturing beyond this point requires very serious bucks and wrenching ability, which includes the commitment of pulling your engine out, disassembling it and adding expensive forced or chemical induction with the attendant forged exotic goodies. This process goes a long way toward lightening your wallet.

The wideband O2 sensor looks very similar to a standard O2 sensor, but should have at least five wires, vs. the one, two, three or four wires of a standard, narrow-band sensor.

Unfortunately, when it comes to naturally aspirated engines, proceeding further than the prerequisite bolt-on mods like intake, header, exhaust, cams and headwork means venturing into a zone of diminishing returns; once there, it takes more work and more money to get proportionally smaller power gains.

Thus, we figured this would be a good place to take a pause in our discussion about buying more expensive parts and learn how to make them harmonize to get lots more cheap, easy power. This time we are going to talk about tuning to win and tuning for power!

Tuning can get you great gains in power for very little hard-earned money. In fact, tuning can be a huge advantage if one knows how to do it and how to test the results. Proper tuning involves some dyno time, which is a definite expenditure, but in most cases, renting an hour or two on the dyno is a lot cheaper than buying a trick part. Spend your time on the dyno with a car that already has the basic bolt-ons and an hour on the dyno could yield more power than that trick part you had your eye on.

Adjusting ignition timing is the quickest and easiest way to find a few more horsepower.

Dyno tuning
Just a few short years ago, the benefits of dyno tuning were only available for race teams that could afford to have their engines run on an engine dyno. This was very expensive. First, the engine had to be out of the car. Second, the dyno shop had to have all of the adapters to mechanically mount your engine on the dyno. Third, the shop had to have all of the electrical hookups to run your engine and ECU; of course, these hookups were usually particular to your individual project and engine. These time-consuming and expensive factors made dyno tuning a luxury the typical enthusiast or amateur racer could not afford.

Adjusting cam timing is something you absolutely need a dyno to do properly. In this case, don't trust the seat of your pants.

This left most of us stuck with two alternatives: going by seat of the pants or quarter-mile time and mph--none of which were repeatable or accurate. Another alternative was using a Clayton chassis dynamometer. The Clayton dyno is not the greatest for the performance tuner. It is designed for mechanics as a tune-up aid so they can get the car rolling at highway speed and observe different things while the car is running. Since it is a brake-type dyno where the dyno rollers are slowed down by either a water or electromagnetic brake, the power measurement is only as accurate as the amount of traction on the rollers and the car's tires.




Coarse fuel delivery adjustments can be made with an adjustable fuel pressure regulator. More precise adjustment is possible through electronic tweaks like the A'pexi AFC.

Since the rollers on the Clayton dyno are smaller than the diameter of the car's tires, it is very hard for even fairly low powered cars to get enough traction to grip the rollers without slipping. Any sort of slipping drastically screws up the accuracy of the test. On your typical brake-type chassis dynamometer, it was impossible to get accurate or repeatable readings on cars with much more than 250 hp. This would be after loading up the trunk with sandbags to help the car get more traction on the small rollers. With front-wheel-drive vehicles, it was often difficult to get stable readings on cars that had more than 120 wheel hp, as it was difficult to pre-load the front tires with additional weight. We tried to use a brake chassis dyno to conduct some testing several years ago and encountered difficulties with wheelspin on a stock Integra GSR. Because of these difficulties, brake-type chassis dynos were used primarily with low-powered cars and the previously mentioned simulation of road conditions.

Seat-of-the-pants power estimation can be, at best, very deceptive, even for experienced tweakers like us. Many times, when working on our project cars, our butt dynos have told us that we had made significant gains in power, only to be proven wrong by actual data from a real dyno. A butt dyno is only marginally better than an opinion.

Do not rely on a simple O2 sensor-based air/fuel ratio gauge. They are not nearly accurate enough in the rich end of the scale. This MoTeC wideband air/fuel ratio meter, or a similar Horiba meter, is vastly better.

Enter the Dynojet. The Dynojet chassis dyno was introduced several years ago as a low-cost way to test high horsepower cars cheaply and with good repeatability. The Dynojet works on a much different principle than a Clayton. On a Dynojet, a computer measures the amount of time the engine takes to spin a large, heavy (4,000 to 8,000 lbs.) roller up to speed throughout a gear range (usually third or fourth gear) from near idle to redline. Since the Dynojet roller is so large, it is easier for a car to get traction on the Dynojet. The dynamic nature of how the Dynojet applies load also reduces the chances of wheelspin. The lack of wheelspin also makes Dynojet readings very repeatable. It is fairly common to repeat in the 1 hp range runs under the same conditions. This makes the Dynojet the favorite for us magazine types, when it comes to testing the latest in hop-up parts.


The Dynojet is what made cheap, repeatable and reliable dyno tuning available to the masses. The Dynojet is fairly cheap to purchase, as dynos go, and does not require a lot of special building modifications such as a concrete lined pit, extra electrical power or high pressure water lines like most dynos. Because of this relative affordability, the Dynojet has been a very popular addition for many local speed shops; most major metropolitan areas have at least one shop with a Dynojet. This is good news for you, the performance enthusiast.

The availability of affordable and accessible dyno time is a potential boon to the performance enthusiast looking for cheap, easy power. In our search for power, we have noted that a good dyno tuning session can yield more power than any single mod you can buy, short of a turbo, supercharger or NOS install (if your car is modified to the extent of having the maximum of bolt-on mods). It is not uncommon to gain 10 hp with a few easy tweaks on a bolt-on equipped car; sometimes, a car with a higher level of adjustability, perhaps equipped with cam gears and fuel pressure regulator, can realize gains of as much as 30 hp! If you want to get more power, rent some time on a Dynojet and go to it. Most shops charge about $100 per hour if you do all of your own wrenching. If you have not had a dyno tuning session before, you will likely walk away with enough power to make that $100 a wise investment in your car's bang for the buck.


The dyno
Dynojets come in two basic versions for automotive use, both of which are labeled Model 248C. One is a low-horsepower version designed to give the best readings for engines making less than 300 hp and a version for more powerful cars making up to around 1200 hp. The main difference between the two depends on the roller weight. The low-power version of the Dynojet has a roller equivalent to about 2,100 lbs and the higher power version has a roller equivalent to 2500 lbs. Only the high-power version is being built currently, but older dynos can be either model. For the tuning of most sport compact cars, either dyno will work. We found that for lower-powered, naturally aspirated cars in the 150-200 hp range, the heavy roller Dynojet can read about 3 to 4 hp less than the lighter roller dyno. This slight difference is only important when changing shops. Dynojets are remarkably consistent for same unit testing, but if you go from a 2,100 lb roller Dynojet to an 2,500 lb one, your results may vary slightly. For this reason, it is best to stick to the same dyno for all of your testing. Both the above-ground and underground versions of the 248C are available in the two different roller weights.

For our testing purposes, we have been frequenting the Dynojet of R&D Dyno Services in Gardena, Calif. [(310) 516-1003]. R&D is a well-kept local secret for many of the fastest racers within driving distance of Southern California. Little known to the masses, R&D tunes many of the fastest Southern Californian racers. R&D can count Russ Matusovich with his 9-second Supra and Signal Auto's chopped top 9-second Civic as a couple of its better known customers. Darren San Angelo, owner of R&D, also builds some of the most powerful engines this side of the Mississippi. Darren is the secret builder and tuner behind many of the West Coast's fastest cars.

The power output of your engine will vary from run to run for various reasons, but usually it is due to heat. The first run will almost always be high, and power should stabilize by the third or fourth pull. If you can accurately monitor coolant temperature, always test at the same temperature. Otherwise, at least allow a consistent amount of time between runs. These three dyno pulls were made back-to- back on the same car. Note how much the power falls off on each run.

Where do I start?
We will talk about tuning adjustments in the order that they should be done for most efficient tuning. Before going to the dyno, it is important to first set your tire pressures and record them. You want to run at the same tire pressure every time you go. If you are raising or lowering the car, it is important to have your alignment set the same way each time as well, as changes in ride height can affect alignment and add power-robbing tire scrub.

Once the car is strapped to the Dynojet, you may want to have the Dynojet operator do a coast-down test. This measures how much power is lost due to driveline friction, but it is also a good yardstick to record variations in power loss due to minor changes in the car's position on the dyno. It is also important to run on the same wheels and tires each time as wheel weight and tire rolling resistance makes a difference from run to run. Any difference in coast-down power loss can be added or subtracted from previous dyno runs to ensure maximum accuracy.

In most cases, you should not use the first dyno pull for analyzing tuning results. The first few pulls often vary by several horsepower as the engine and transmission get hot. Obviously, the engine should be fully warmed before starting, but there will still be changes as the engine heats up from idling temperature to full-load temperature.

The Dynojet's smoothing function filters out the vibrations that the dyno's sensors pick up. You should always run with smoothing at least on 3, and in some cases, even higher. Either way, only compare runs with the same smoothing factor. These two printouts are the same dyno run. The one on the left has the smoothing at 0, and the peak power is listed as 178.9 hp, while the one on the right, with a smoothing factor of 5, says 161.4. The higher value was read off a spike. The real power output is 161.4 hp.

Most naturally aspirated cars make the most power on their second pull and have their stabilized power on the third or fourth pull. This is usually a result of the car's intake tract getting heat soaked. Turbocharged and supercharged cars usually make their best power on their first pull before the intercoolers and intake tract becomes heat saturated. This variation can be as much as 5 hp in a naturally aspirated car or, amazingly, as much as 30 hp in an intercooled turbo car running lots of boost! Make sure the car has been driven for at least 15 minutes of freeway driving before dynoing; a cold gearbox with thick oil can rob as much as 3 to 5 hp. If you have an accurate coolant temperature gauge, running the car at the same coolant temperature on each run greatly reduces run-to-run variations.

You should also run the dyno tests at the same smoothing factor each time. The raw data coming from the dyno's acceleration sensors is quite jagged and noisy, so the dynojet software is equipped with smoothing algorithms to average out the bumps and spikes. A lower smoothing factor can show a higher power peak if there happens to be a spike near the top of the powerband, but that is not a realistic way to judge increases of power. A smoothing factor of three is usually good for tuning.

A new feature available on some Dynojets is an air/fuel ratio measurement. Sampling exahust gas with a wideband O2 sensor, these Dyojets can plot horsepower, torque and air/fuel ratio at the same time. This kind of detailed information can be very useful when adjusting fuel delivery.

Run the car with the hood up and, if possible, have a fan directed at the air intake to prevent hot air from radiator fans from throwing the test off. We have seen variations of as much as 6 to 9 hp from the radiator fan clicking on and blowing hot air into the intake during a test. Finally, make sure the dyno operator diligently enters the correct humidity and the dyno's barometer and temperature sensors are working correctly. That being done, you are ready to do some adjustments and make some horsepower!

Ignition timing
The ECU or Engine Control Unit in your car is usually programmed on the conservative side. It has an ignition curve programmed so that if some cheap sap fills the tank with 87-octane pee water, all will be good and no damage will occur. Since you are a hardcore performance nut and are willing to shell out the extra coinage to feed your steed 92 octane fuel, there is usually some power to be gained by advancing your ignition timing.

Once the car is strapped to the Dynojet and the readings have stabilized, try advancing the timing two degrees at a time and observe if your power increases. On most cars it will. If you go more than 4 or 5 degrees more advanced from the factory spec, use extreme caution. Do not tolerate any detonation at all. Detonation can damage your engine, so don't let it go on for more than a second or two. If you hear the telltale ping or metallic ring, back off the gas at once. We covered detonation and what it can do to your engine in detail in our first installment of this series (August, '99).

You will have to refer to your factory service manual for the exact instruction on how to adjust the timing. On most cars this is done by loosening the bolts that hold either the distributor or in some newer cars with distributorless ignitions, the crank angle sensor. Don't just guess and twist; use a timing light and do it right. On a very few cars, the timing is not user-adjustable (such as the Nissan Maxima or the Golf 1.8T); in this case, you will have to rely on the tuning skills of the professional chip smith like Jim Wolf Technology for the Nissan or AMS for the VW.

Don't assume that if some advance is good, more is better. Advance the timing in two degree steps until the power either flattens out or decreases and back down slightly from there. Later, when road testing your car, if you note any detonation, you may have to reduce your timing even further because the real road loads the car a little differently than the dyno. Typically you might pick up 2 to 5 hp by experimenting with better fuel and advancing your timing. Cars that have a chip or tuned ECU are not likely to get much, if any, safe gains by adding additional timing.

Cam timing
Most cars have their cam timing set at the factory for minimum emissions; production of maximum power is a secondary goal. As we explained in the third segment of this series, most production camshafts are designed for minimum overlap with a wide lobe separation angle to reduce hydrocarbon emissions and to ensure a smooth and stable idle. If power is your priority, a few horsepower is usually available to those who are willing to spend a little time with tuning. Adding little bolt-ons like air intakes and headers can also change the optimal cam timing that your car prefers. VTEC-equipped Hondas and Acuras with their big duration secondary lobes and cars that have big cams fitted with headwork and lots of other mods can almost always benefit from some cam timing adjustment.

Another interesting fact is that almost all aftermarket and many stock cams are usually ground a degree or two off from the spec that they are supposed to be ground to. This is normal variation of tolerances in production. Dialing in the cam timing allows the tuner to compensate for these slight errors. Often there are a few hp just waiting to be unleashed by this alone.

As most sport compacts have DOHC engines, we will start with the assumption that your car has two cams. (If you don't know what DOHC is, please refer part three of this series in the June 2000 issue, where we discussed camshafts in detail.) To adjust your cam timing, you need to purchase adjustable cam timing gears.

While dyno tuning, if you progress in the adjustment orders listed below, you can usually get results with a fewer number of dyno pulls than proceeding willy-nilly. You don't necessarily have to go through the whole sequence of adjustments when tuning; if a series of adjustments starts to make good results, continue in that direction, do not go through the whole sequence. For instance, if advancing the intake cam moves the powerband to where you want it, you don't need to try retarding the cam as well.

The accepted way to dial-in a cam is to start with the intake cam, since most street-type engines respond well to having the intake cam advanced. Advance the intake cam 2 degrees at a time, testing between adjustments until the power falls off or the desired powerband is met. If the power falls off right from the get-go, try retarding the intake cam, although this is not likely to be the best solution on most street engines. After adjusting the intake cam, most tuners first retard the exhaust cam slightly. Try retarding the exhaust cam in one to two degree increments until the power drops. If the engine does not respond to this, try advancing the exhaust cam. Many engines seem to like having the intake advanced 4 to 5 degrees and the exhaust retarded 1 to 2 degrees. My take on this is that doing so increases overlap which, done in moderation, tends to broaden an engine's powerband. This also helps production-type engines with their more restrictive ports, intakes and exhausts (as opposed to real, race-specific engines) breathe better at mid and high rpm. As a warning, this is very general and must be verified on a dyno, as many engines will not like this either!

With SOHC engines, like the venerable D series Honda Civic engines, there is not as much flexibility in cam timing adjustment; you are confined to advancing or retarding everything, because the intake and exhaust lobes are on the same stick. This limits you to moving the powerband around, more than broadening and lowering the powerband or making the power peak higher and more narrow--options that you have on DOHC engines. When dyno tuning an SOHC engine, you should experiment first with advancing the cam, then retarding it. Two-degree increments usually make a big enough change to easily spot on the dyno.

When adjusting cam timing on the dyno, remember: It is better to go for an area under the power curve rather than maximum peak power. Having 4 more horsepower from 5500 to 7800 rpm will get you down the track faster than having 7 more from 7500 to 8000 rpm-- and less everywhere else. Adjust the cam timing to get the most power in the rpm range, where the car will be pulling the longest in each gear.

As a warning, piston-to-valve clearances decrease when advancing the intake cam. Usually this is not an issue in stock engines, but with a higher lift and long duration racing cam with milled heads or other modifications, it is possible to hit the intake valves on the piston and cause damage. In most cases, you can safely advance the cam on a street engine at least 6 degrees before you need to worry about contact; however, if you are not sure, measure the clearances before proceeding. A mistake can be costly.

It can be possible to see gains of up to and more than 10 hp by optimizing cam timing, although 3 to 5 hp across the rpm range is usually more typical. It is also important to remember that any change to the engine, especially to the intake and exhaust system can change the cam timing that the engine likes. It is also important to know the engine may like slightly different ignition timing after the cam timing has been set, so it might be a good idea to play with that again, after optimizing the cam timing.

As a final note, don't forget that many cars drive their distributors off the back of one of the cams, so a change in cam timing will also cause a change in ignition timing. If your engine has such a distributor, re-set the ignition timing after each change.

Fuel pressure
Due to the fact that auto manufacturers have no control over how the end user is going to drive and what octane gas will be used, the wide-open throttle air/fuel ratio programmed into the cars ECU tends to be set on the rich side. A richer fuel air ratio burns cooler and is safer by being more resistant to detonation. Modern engines are programmed to run a tick richer than stoichiometric (the 14.7:1 ratio that is perfectly balanced chemically for complete combustion) at low speeds and light throttle, because this is where a catalytic converter works at the greatest efficiency. At wide-open throttle, best power is usually obtained at a richer mixture ratio of about 12.5:1 to 13:1.

For an extra margin of safety, most modern cars run a more conservative 11.5:1 to 12:1 mixture (remember, lower ratios are richer) at wide-open throttle to aid cylinder cooling and reduce the chance of detonation with low-grade fuel. Some really conservative companies, and most factory-turbocharged engines, run as rich as 10.5:1 at wide-open throttle.

To get more power, most cars (if you intend on running only premium fuel) will respond to being leaned out a little at wide-open throttle. The best way to do this is by reprogramming the ECU, but since the ECU code is not well known for many cars, other means will have to be used. For Hondas, Zdyne and Hondata make innovative user-programmable factory ECUs. For Nissans, Jim Wolf Technology is a well-known choice. For the 1.8T VW engine, there are a plethora of chip burners and for the FD RX-7, there is the Apexi Super FC. If there are no choices like these for your car, there are always the aftermarket stand-alone ECUs such as DFI, Motec, Haltech, EFI Technologies, Electromotive and others. The tuning of these units is way beyond the simple tuning tip of this article and will not be discussed here.

If your car has a MAF (Mass Air Flow) monitoring fuel injection system, then chances are it can accept minor modification to the engine, like headers, exhausts, mild camshafts, cam timing tuning and air intakes with no or only slight changes to the air/fuel ratio. Cars like Nissans, Toyotas and Mitsubishis made in the mid '80s and later, for the most part are equipped with MAFs. These types of fuel injection systems measure the amount of air coming into the engine so the engine control computer knows how much fuel to inject for a proper mixture. If a mod improves volumetric efficiency and causes more air to be ingested by the engine, then no problem, the MAF picks it up and the ECU compensates within reason. Of course, huge changes in airflow, like adding superchargers or turbochargers, will be beyond the ECU's ability to compensate, but most bolt-ons can easily be accommodated.

On MAF-equipped cars, it may help to disconnect the battery for a few minutes to reset the self-learning function of the ECU, so the ECU can relearn the new mixture required. It may also take a little driving for the engine's ECU to adjust to the new mods. Generally, the engine will run better and better for the first 20 or so minutes of engine operation after installing new parts.

A few popular imports use what is called a speed-density airflow metering system. Hondas and Acuras are the main example, although the latest Subarus and most domestic sport compacts are speed density also. These cars use a MAP or Manifold Absolute Pressure sensor to help the ECU determine how much fuel to inject for a correct mixture. This sensor reads manifold pressure or vacuum, which, together with data from the throttle position sensor, gives the ECU an idea of how much fuel to inject into the engine. Unfortunately, most speed density systems do not compensate for modifications very well. A MAP-equipped car can lean out if camshafts, air intakes and other goodies are added to the engine.

All is not lost, however. You can add a device called a fuel pressure riser. This is a vacuum-referenced adjustable pressure regulator that goes in the return line to the gas tank. A fuel pressure riser has a manifold vacuum reference port that goes to the intake manifold. By using this reference, the riser can richen the fuel mixture, mostly at wide-open throttle. With a fuel pressure riser, you can control the fuel pressure to the injectors, allowing you to increase the pressure to add more fuel in order to make up for the additional air being drawn into the engine. Stillen makes fuel pressure riser kits that can be adapted to many speed density-equipped cars. Hondas using ram air systems almost certainly need to run more fuel pressure to avoid leaning out at high speeds; tuning these is best done at the track. Turn up the fuel pressure 5 psi at a time until the trap speed falls, then back up to the previous best trap speed.

A disadvantage to the fuel pressure riser is that it cannot reduce fuel pressure to lean the mixture. In that case, a fixed pressure regulator can be used. There are many of these on the market, like the Weapon R fuel pressure regulator, among others. The disadvantage of these is that they richen or lean the fuel air mixture everywhere, under part throttle and full throttle. The engine's self learning control can compensate up to about 10 percent for most cars, but there is a limited range to where the regulator can richen or lean out the mixture without affecting drivability at conditions other than wide-open throttle.

Another way to fiddle with the mixture a little is with an electronic fuel device like an A'PEXi AFC. This alters the MAP or MAF signal to fool the ECU into injecting more or less fuel. This works well for fine tuning, but trying to adjust more than plus or minus 10 percent on the fuel air ratio can cause many cars to go into fail-safe mode or cause the AFC to fight the ECU's self-learning function. It is a pretty handy and precise way to make fine-tuning adjustments to the air fuel ratio.

Optimizing the air/fuel ratio for more power will increase cylinder pressure. This may cause detonation, necessitating a reduction in timing. In other words, you may have to do some fiddling between optimal mixture and timing for best power. As a rule of thumb, if you are suffering from borderline detonation at your optimal power tuning point, it usually affects the power less by richening the mixture to suppress detonation rather than reducing timing. In other words, try adding fuel first before taking out spark.

The best thing to do is to first try slightly leaning out your mixture on the dyno in 5 percent increments on your fuel controller or by trimming your fuel pressure by 5 psi or so at a time. If the car makes more power, go a little more at a time until the power gain flattens out, then richen a little until just before the flattening point.

Be extremely careful; do not tolerate any detonation and use only premium fuel. It is not a good idea to go much past 10 percent leaner. If going leaner does not help, try going richer using the same methodology. Going richer is much safer. MAP cars are much more likely to gain power than MAF cars. If you are increasing fuel pressure to richen the mixture, it is very dangerous to exceed 80 psi of fuel pressure because this is the point where many injectors can stick, due to increased side loads on the injector pintle. This can cause erratic running and a dangerous, overly lean mixture. Eighty psi is very extreme; while you should never be turning the fuel pressure up this high on a naturally aspirated car, it is possible for a bolt on supercharger or turbo kit with a maladjusted rising rate fuel pressure regulator to run this high.

If you are trying to see gains from a car with a tuned ECU, you are not likely to get very much out of fiddling with the mixture; if the chip burner knew what he was doing, he took a lot of the compromise tuning out of the program as it is. In that case, you must be even more careful not to go too lean. Usually, it is futile and possibly dangerous to try to tune more power from a tuned ECU.

If your dyno shop has a broad band air/fuel ratio monitor with a five-wire O2 sensor, that can be a useful tool for tuning safely. As we have explained many times before in this series, running lean means more heat and a greater chance of experiencing detonation. Do not tune a naturally aspirated car to run leaner than 12.5:1 or tune a turbo or supercharged car much leaner than 11.5:1, unless you can feed it really good racing gas. Remember, more boost means a richer mixture is safer and mixtures of 10.5:1 are really much safer for a pump-gas-burning turbo or supercharged street car. Motec and Horiba both have good A/F ratio monitors. Do not use the cheaper A/F meters on the market for tuning; they are not accurate enough. If in doubt, check how many wires the O2 sensor for the meter has. If it has five wires, it is a broad band and safe for tuning use; if it only has three to four wires, then it is not acceptable for tuning.

We have been able to get from 0 to 10 hp by tuning the fuel mixture on bolt-on equipped street cars.

Read those plugs
The lost art of reading plugs is an important skill for tuning, especially when it comes to judging the correct amount of timing advance and how lean the mixture is. Reading plugs involves looking at the porcelain insulator of the center electrode and the general condition of the center electrode and ground electrode. To read plugs, it is handy to have a magnifying glass and a light--or better yet, a lighted magnifying glass. When the car completes a dyno pull, the engine should be quickly shut off and the plugs inspected without having the car idle for a long period.

The first thing to look for on plugs are signs of detonation. The usual signs of mild detonation are dark gray or silvery specks that contrast against the light colored porcelain of the center electrode, much like pepper on a white dinner plate. The specks are about the same size or slightly smaller. Unfortunately, the specks are caused by aluminum being vaporized off the tops of your piston or the combustion chamber by the heat and pressure of detonation! If you look at the ground and center electrode, you may see, on a detonating engine, tiny dingle balls that look like spherical weld splatter. These are small--so small it may only be possible to spot them with the magnifying glass. The ground and center electrode may have a blue-green to straw yellow tinge on it as well.

If you see these clues, you may not have heard the detonation over the roar of the engine on the dyno. You need to either add fuel, back off the timing or a combination of both (whichever causes the least loss of power) or serious damage to the engine will result. Broken ring lands, burnt valves or sometimes even holed pistons and pounded rod bearings result from detonation. In more dire cases of detonation, the ground electrode may be completely or partially melted away. In even worse cases, the ground electrode may be damaged or destroyed. In very severe detonation, the porcelain center electrode insulator may be fractured and partially missing from the hammering pressure waves of detonation. If you observe damage like this to the plugs, it is prudent to do a compression and leak-down test before proceeding further as you have probably seriously wounded your engine.

You can also determine if your engine is running too rich or too lean by looking at the plugs. With modern, unleaded pump gas, the proper mixture nowadays will have a center electrode porcelain color ranging from bone white to medium brown. In the old days, due to the large amounts of lead found in gasoline, the trick was to shoot for a chocolate brown. This would be terribly rich using modern fuel. Pump gas usually colors to about bone white to light tan and racing fuels are from light tan to medium brown. Modern racing fuels increase octane mostly by the addition of heavy, long-chain aromatic hydrocarbons rather than adding high concentrations of poisonous, plug-coloring tetraethyl lead as they did in the old days.

If an engine is running too lean, the center electrode will be bleached white with kind of a flaky, peeling look, like it was sandblasted with really coarse sand. Usually, a plug running this lean will also show signs of detonation. Too rich will be a dark brown or black plug covered with dry soot. Serious rich will be black and wet, smelling strongly of gas. Fuel-injected cars seldom have a situation like this unless there is a malfunction, like a stuck injector or super high fuel pressure sticking an injector pintle. A worn engine burning oil will have the plugs covered with a sticky black carbon.

A plug's heat range should also be considered. The heat range is a rating of the plug's ability to conduct heat away from the center electrode. A stock plug is usually a hot heat range, so the plug does not foul up while spending a lot of time idling and driving at low speeds. Racing plugs are cold plugs, so the center electrode will not get too hot and contribute to detonation. However, racing plugs will quickly foul with carbon deposits driving at low-street speeds. For a bolt-on modified street engine, you can figure out the part number coding on the type of plugs your car takes and install one heat range colder if you are running at high speed for an extended amount of time (e.g. on a road course). If your engine has higher compression or a turbo, blower or NOS added, you should automatically go at least one heat range colder and possibly two, if you are doing some track driving. If you are only racing a heavily modified car with no street driving, racing plugs several heat ranges colder may be needed.

We hope that you have learned some of the basics to tune your engine. Like we said before, investing a few hundred dollars in dyno time will usually get you more power per buck in a mildly built car than any similar value of shiny, expensive go-fast parts.

So go ahead, buy those parts, learn how.

The lost art of reading plugs is an important skill for tuning, especially when it comes to judging the correct amount of timing advance and how lean the mixture is.

If you look at the ground electrode, you may see tiny dingle balls that look like weld splatter

Basic Dyno Tuning Tips


1. Have a plan on what you are going to adjust and learn how to do it quickly before you get to the shop. When the clock is ticking, you don't want to be figuring out how to adjust your ignition timing or fuel pressure. Maybe even practice, doing a dry run before you go.

2. Bring your own tools. Bring the right tools. Most shops don't like loaning tools to customers.

3. Read this guide before you start making adjustments, so you don't blow things up.

4. Change only one thing at a time. Take exact notes of your changes.

5. Many shops won't let customers work on their own car while on the dyno. In that case, come with a plan for which adjustments you want to try and get the dyno tech to agree to it before starting. In this case, prepare to pay a little more. Another alternative is to go to a Dyno shop with a good local reputation for its tuning ability and just hand over your car. For some of our project cars, we use R&D Dyno Services with good results.

6. Most shops will make you sign a waiver saying that they are not responsible for blowing up your car. Don't worry, if done correctly, dyno tuning is pretty safe.
dan_b
 


Postby Camile » Wed Sep 20, 2006 5:14 pm

just a wee bump as these have been moved to this section. now you know they're here :wink:
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Space. It seems to go on forever, but then you get to the end and a gorilla starts throwing barrels at you.
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