Dyno Tuning Tips
The process of tuning your vehicle on a chassis dynamometer is a perfect example of a controlled scientific experiment, and we will encourage you to use sound scientific methods in order to obtain the most valid results.
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1. Determine what variables are going to be changed ahead of time. There are a great number of things one can change that can affect an engine’s power. Relatively simple changes that are commonly performed while dyno tuning include changes in timing, valve lash, boost pressure, fuel pressure, swapping spark plugs, wires, distributors, mufflers, carburetors, jets, fuel injectors, throttle bodies, and pulleys. Changes that are not normally performed while dyno tuning include swapping heads, manifolds, and internal engine components. These changes can be very time consuming, and one does not want to be paying for a dyno rental while performing the work. In these cases, it is best to perform the work away from the dyno.
2. Determine an order for changing the variables. If one is going to be resetting each change back to the original state before going on to the next change, then it doesn’t matter what the order is. If combinations of changes are going to be tried, then a logical run order is essential.
3. Change only one variable at a time. This point can not be stressed enough, and the reason is simple. If one changes multiple variables simultaneously, one will not know which variable affected the outcome.
4. Eliminate deviations in other variables, or at least determine and record what the deviations are so that they can be factored into the experiment. Engine temperature and tire pressure are two such variables. Tire pressure is normally not a concern unless the vehicle is on the dyno long enough for the tires to heat up, or if days or weeks separate the dyno runs, but engine temperature is always a concern and it can have a significant effect on the power generated. Forced induction engines are especially susceptible to changes in temperature. As the engine heats up, so does the turbocharger or the supercharger, forcing the incoming air to heat up as it travels through all of that hot steel. This condition is known as “heat soak.” It is essential to perform multiple baseline runs to see if there are any changes in power as the engine heats up. If there are significant changes, it will be necessary to maintain a specific temperature while performing the rest of the experiment in order to obtain valid results.
5. Perform multiple baseline runs to determine your vehicle’s normal power variation. Even if all other conditions are identical, some vehicles will experience significant changes in their power output between dyno runs. In some cases, this can be an indication of a problem, such as fuel delivery or spark problems. Evidence of this may show up as a choppy curve on the graph. In other cases, it is simply an inherent result of the engine’s design. It is not the fault of the dyno, as many vehicles can perform multiple tests spread over many weeks, and have all of the results fall within 0.3% of one another.
6. In all cases it is of critical importance that one does not assume that power gains or losses that are within the normal variation are the result of a variable that was changed. This is a very common mistake, and it is made by even the most experienced dyno technicians. If a 300 hp vehicle shows very repeatable results that are within 0.5% of one another, the runs are still going to vary by up to 1.5 hp. Therefore, it is not scientifically accurate to claim that a spark plug swap produced a 1 hp gain after performing only one run. Most vehicles do not show such repeatable results, and many high-horsepower engines can routinely vary by 5+hp, even if all of the monitored variables are identical. Sound statistical methods can not be ignored; one must perform multiple runs and calculate the average.
7. Record as much data as possible. Bring a notebook, and write down everything that happens. This most important aspect of dyno tuning is also the easiest to perform and the most often neglected. At Bristol Dyno, customers have unlimited runs while renting the machine, and fifteen or more can easily be performed within one hour. Don’t expect memory to be infallible. I will be able to record a minimal amount of information on each run, but it is up to you to make sure that all of the data that you want recorded is recorded. As with most experiments, a great deal more time can be spent analyzing the data than on the testing itself, and an accurate record of the testing is crucial. One can easily leave the shop with twenty pages of graphs and tabulated numbers, and if an accurate record was not kept, meaningful conclusions will be unobtainable.
8. Don’t be surprised if no or minimal power gains are made, especially if the vehicle is stock. It may come as a surprise to many people, but many automobile manufacturers know what they’re doing, and their stock vehicles may very well be tuned as close to perfectly as is practical. If every change you make while dyno tuning lessens the vehicle's power output, then you can leave assured that your vehicle was performing as well as it could have been when you arrived.
9. Unless you have hard evidence from a similar vehicle, do your best to arrive without any preconceived notions as to what will give your vehicle the most power. Science has spent hundreds of years disproving hearsay and "old wives tales," please don't ignore it now. The best scientists will be, or at least successfully pretend to be, completely ignorant of the possible outcome when starting an experiment because they know that failure to do so may affect the results. The most common mistakes people make are with the use of freer-flowing intakes and exhausts, and changes in timing and fuel delivery. New intakes and exhausts can make significant gains in many vehicles, but if air flow through your particular vehicle's engine was not a restriction before, installing a less-restrictive intake and/or exhaust will not make any difference, or it may make things worse. See the dyno charts from someone else with an identical vehicle that already tried it before you spend the money. Many customers are told of their optimum timing and air/fuel ratios before they arrive, sometimes by even a very experienced, knowledgeable mechanic or engineer. They may be right, but chances are that they will be wrong. Every engine is different. When your vehicles is strapped to the dyno, you have a very powerful diagnostic machine at your disposal - don't be afraid to use it because you trust the person that told you. If you were told that 32 degrees of timing was optimum, try 28, 30, 32, 34, and 36 to see for yourself. The same holds true for the air/fuel ratio. The best example of an erroneous preconceived notion that I have seen so far is that removal of the air filter will increase power. Many times I have seen the removal of the filter increase air flow and lean the air/fuel mixture to such an extent that the engine lost significant power. Many times I have also seen customers try and explain away such surprising results because they didn't believe that they could be true - don't make the same mistake.
10. For the love of God, DON'T TRUST MANUFACTURERS' HORSEPOWER CLAIMS. This holds true for the manufacturers of aftermarket bolt-on parts more so than the automobile manufacturers, but it is certainly true for everyone. I purchased a cold-air intake from one of the most well-known and reputable aftermarket performance part manufacturers in the world. It came with a dyno chart showing the effect on horsepower before and after installation of the intake on my car. I didn't realize it until after I opened this business and I took a closer look at the chart, but IT WAS A HAND-DRAWN DYNO GRAPH. Why would a multi-million dollar company not show a real dyno chart? Manufacturers are going to inflate their claims to get you to purchase their parts. The somewhat reputable ones will at least write "as much as..." before the horsepower claim, and it is doubtful that your vehicle will be set-up identically to the manufacturer's test vehicle. For example, a vehicle owner may install five different performance parts from five different manufacturers. Each one promises a 5hp increase, so the owner naturally assumes that he increased his vehicle's power by 25hp. If he is lucky, he got at least a 25hp increase. There is also a chance, however, that the parts weren't made to work with one another, and the increase was far less than 25hp.
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