There's always someone at a car show bragging about how their custom ride is faster than the speed of sound and may even have a dyno sheet allegedly proving this outrageous claim. While certainly annoying, the real problem with skewed dyno test results is when parts manufacturers use them to make their products appear to add more horsepower than they actually do. Thanks to a handy video from high-performance internal combustion engine maker, Banks Power, you can tell if a dyno sheet is legitimate or not and put that car show blowhard in his place, as well as decide whether to actually purchase a performance-enhancing product.

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The Science Of Torque And Horsepower

To the average gearhead, the science of speed is about as interesting as a seminar on the latest insurance regulations. They just want to know how fast their car is and how to make it faster. It is however important to understand what torque and horsepower are in order to measure them and improve upon them. When you see an automaker list the horsepower for one of its vehicles, there's a 100 percent chance that the engine was tested outside of the vehicle and doesn't represent the power made when the wheels hit the road.

To get a true measure of real-world power, a vehicle needs to be tested on a chassis dynamometer (dyno), which is the type most are familiar with. On a chassis dyno, the car runs on rollers that measure torque and rotational speed (RPMs), which is then calculated into horsepower. It can be adjusted with resistance to replicate actual driving conditions, like hauling a load or driving up a steep incline. Dynos can also be tuned to compensate for atmospheric conditions that affect a vehicle's power

Torque is the twisting force that it takes to make an object rotate around an axis and is measured in foot-pounds. In layman's terms, as it relates to the automotive world, it's the amount of power it takes a vehicle to reach a certain speed. Horsepower on the other hand is the linear power of the vehicle. One horsepower is equal to a horse lifting 550 pounds one foot in the air in one second. There's a lot of dense science behind all of this, but Toyota explains it best by noting torque is what you feel when you launch from a dead stop and horsepower is what you feel as the RPMs start climbing. Torque measures what an engine can do at a given moment and horsepower is what the engine can do over a certain time.

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How To Cheat A Dyno Test

Banks Power dyno test rear wheel view
Banks Power / YouTube
Banks Power rear wheel view of dyno test

Obviously, a dyno operator can skew the results of a test by imputing bad perimeters, but if done properly there should be no difference from one dyno to another. The issue is that a dyno test is supposed to reflect an engine at sea level with a high oxygen content in the air. Running a test at higher altitudes where the air is thinner, will produce worse results. Additionally, engines produce more torque in colder weather, so testing in a hot and humid climate will also show less power. Because of these differences, dynos have "Correction Factors" that can be input to compensate for altitude, temperature, and other variables.

Unscrupulous after-market parts companies can exploit these differences to make it seem like their doohickey increases horsepower when it actually does nothing. It's something that MotorTrend has been warning about for years. A company could run a baseline test of the vehicle with poor conditions that would rate it as less powerful than it is, then bolt on their part and run another test under optimal conditions. The difference between the two tests would show that their part increased horsepower when in reality there was no change because the runs were not equal. In the video, Banks Power busts several companies for "sandbagging" an initial test before falsely claiming their products increased the power of an L5P Durmax engine in a second test.

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Three Ways To Catch A Cheat With A Dyno Sheet

Catch a cheater with a dyno sheet
Banks Power / YouTube
banks Power shows how to catch a cheater with a dyno sheet

Before you go buying an aftermarket part to increase your vehicle's performance, Banks Power gave three ways to spot a cheater, using nothing more than the dyno sheet. The dyno sheet shows the torque and horsepower curves, but it also has the atmospheric conditions like temperature, humidity, and time of day when the test was conducted at the bottom. The first way to spot a cheater, as was already hinted at, is if the baseline test has different conditions than the second test. When the two tests don't match identically, the data is flawed.

The second way to bust a cheater involves some math and may not be for everyone, or anyone for that matter. One would have to understand how to calculate horsepower from a torque curve, which sounds about as fun as sitting through all 7 Police Academy films in a single sitting. If you were able to make this calculation, you could look at the arcs on a dyno sheet and be able to tell if they were consistent or if someone had Photoshopped a higher horsepower. Again, this is for rocket scientists and data wonks only.

The final and best, way to catch a dyno sheet cheater is to look at it. The notes at the bottom detailing the atmospheric conditions tell all. If the Correction Factors were added when it wasn't called for like if the dyno compensated for air density or temperature when it wasn't necessary, the results are completely bogus. When that car show blowhard waves his dyno sheet in your face, bragging about his 700 horsepower custom job, you can easily call BS by looking at the notes.