Maybe you’re asking what’s going to happen when you bring your vehicle in for it’s first dyno test. Maybe you’re looking for medical procedures and you came across this page by accident. Either way, I’m going to tell you what’s going to happen to your vehicle.
First, I will explain to you what is going to happen and exactly what a dynamometer test is and what it does to your vehicle. Then you are going to sign a waiver stating that I explained everything to your satisfaction and you understand exactly what a dynamometer test is and what your risks are. Risks? What risks? Unless I forget to chock your wheels and/or strap your car down, the only risk to your vehicle is the same that you encounter on the street every time that you floor the accelerator pedal and hold it there until the tachometer nears the redline.
Something on your vehicle might break. Just because it happens while your vehicle is being tested doesn’t mean that the test broke your vehicle. The drum of an inertia dyno is sized to approximate the forces that a typical vehicle encounters when it accelerates itself down the road. After learning about the dynamometer test, if you refuse to sign the waiver, I will refuse to test your vehicle.I will then inspect the general condition of your vehicle. If it appears that your vehicle is likely to experience a failure when the accelerator is floored (if your vehicle is a piece of junk), I may not test it. ]
If we both decide that your vehicle is going to be tested, I will strap your vehicle securely to the floor and place chocks before and after the non-drive wheels. Securing a vehicle to the floor can prove to be very difficult in some cases, so if you happen to know of some good points to hook onto your car, please let me know – it will save a lot of time for the both of us. If your tire pressure look or feels low, I will measure it. If it is low, I will inflate it to the manufacturers recommended pressure. Keep in mind, tire pressure may have a significant effect on the test results, just like it have on a drag race. My reasons for checking tire pressure are for safety, not for achieving the optimum test results. If you want optimum results, you must research the best tire pressure on your own, I will only make recommendations based on my knowledge and experience.
The next step is to open the hood and place an inductive pickup on one of your spark plug wires (or one of your coil wires.) This is how the computer will measure your engine’s rpm. Lately, some auto designers have made spark plug wires very difficult to access and have hidden them entirely in many cases. If you own such a vehicle, help me out and tell me the easiest way to access a wire. If a special tool is needed to remove a cover, be sure to bring it. If you
want to be really nice, remove any covers before you arrive or while I am strapping the car down. At some point, I will enter your vehicle’s description, your name, and some other parameters into the dyno computer. Parameters include the redline on your vehicle’s tachometer and the speed rating on the tires to provide limits for the test. Once the speed rating is entered, the dyno will not exceed that speed during the test, and I will most certainly not
enter false speed rating so that you can get a test result at a higher speed. If you want the test to exceed 150 mph, make sure that you have at least Z-rated tires. Dyno will go 225 mph.
Your vehicle can be tested in one gear, or in all of it’s gears. Theoretically, the results should be the same regardless of what gear is used because the increased torque in the lower gears is canceled be the decreased speeds. In the real world, there are always differences between the gears, and the differences can be explained by a number of factors.
Because of nasty things like friction and inertia, different gears always have different amounts of drag, and the greater the reduction or increase in the gearbox, the greater the drag. A low gear may fly the engine through the rpm range so quickly that it never hasa chance to build up any useful intake and exhaust resonance that those header engineers spend so much time trying to achieve. Fifth gear may be spinning your drive train so quickly that significant increases
in gearbox drag are created. Third and fourth gears are usually favorites for finding your actual horsepower, and testing all of the gears it a useful method for discovering problems in your drive train. Many dynamometer operators go right for the gear that is the closest to a 1:1 ration as it has the lowest drag in the gearbox and therefore the highest horsepower reading (usually) on a vehicle that is properly sized to be tested on this dyno. Of course, many cars don’t have true 1:1 gear ratios, and many cars are not the exact proper size that the dyno was designed for, so blindly going for the gear ratio that is closest to 1:1 is not always the right answer.
You may also elect to have some air/fuel metering done during a run. This information will be plotted on a graph just like your horsepower and torque, and you can see how the air/fuel ratio changes with your engine rpm. In most cases, the meter samples air coming out of you tail pipe. I can also replace one of your vehicle’s O2 sensors with the one in the air/fuel meter, or if you’re really serious, you’ve made an extra threaded hole in your exhaust system that my O2
sensor will fit into. In most cases, the tail pipe method works great. If you still wish to replace one of your O2 sensor with mine, you need to make sure that your vehicle will function properly with the original sensor disconnected. If it won’t, you have to bring and “oxygen sensor simulator” to plug into your wiring harness that will trick your vehicle’s ECU into thinking that everything is working properly. Look for them on the internet.
So now you’ll need to decide what kinds of runs you want to use during your test. If you want to know what your horsepower is, go for three fourth gear runs. Three separate runs will allow you to weed out any anomalies and it will prove the repeatability of the equipment. It will also allow your vehicle to warm up, and if you so choose – cool down.If you want to do a quick diagnostic test of your drivetrain and see the differences between your gears, try a run in third, fourth, and fifth gear. If you suspect problems with your drivetrain, ask about a Negative Horsepower test. If you’re a racer, engine builder, or tuner with distinct goals in mind and you know how to achieve them, rent the dyno.
Be prepared to pay more for the Negative and Dynotrac test and the air/fuel metering, because they take more time andcause more wear on the equipment. See the PRICING page for more information.Once the test is complete, the computer “corrects” the data. Environmental conditions such as temperature and atmospheric pressure have a significant effect on the horsepower that an internal combustion engine produces. Fortunately, this effect is well understood and easy for a computer to account for. In order to make useful horsepower
comparisons, most test results are tweaked so that it appears that the test was conducted at a specific temperature, pressure, and humidity. In the United States, the most common correction factor is SAE J1349. This standard makes it seem that the test was conducted at 77°F, 29.23 in. of Hg pressure, and a humidity of zero. If you want your horsepower corrected to a different standard, such as EEC (popular in Japan), DIN (popular in Germany), or “standard
corrected,” you must let me know before I print the results. Remember, the standards use different atmospheric conditions and the will all return different horsepower values. “Standard corrected” is popular with aftermarket manufacturers because it uses a higher pressure and a lower temperature (denser air), thus inflating the horsepower numbers. If you want bragging rights over your peers, make sure all of you use the same standard. You certainly
don’t want to be seen whipping out your calculators before you go street racing.
You will receive aprintout of your vehicle’s test results which will consist of a graph plotting horsepower and torque vs. engine rpm (or speed, if you choose.) You will receive a graph plotting your air/fuel ratio vs. rpm if you elected to do such a run, and you may also receive a text printout in tabular form of the hp and torque vs. rpm of speed of each run if you wish.