Taking your car to a dyno is often a great way to produce bragging rights, especially after installing various aftermarket modifications. Following the results owners often swear by the figures, but variances in the equipment itself can lead to numerous results that skew the figures themselves.
Engineering Explained tackled the subject of dyno testing with host Jason Fenske's personal Honda S2000. After four runs, the first three produced consistent horsepower ratings, but torque measurements significantly varied. In this case, the dyno thinks the peak rpm is much lower than it is. The S2000's redline sits at 9,000 rpm, but the dyno figured it to be around 6,500 rpm.
Therefore, the dyno calculated the engine was not revving as high as it actually did. Torque and rpm are inversely proportional in a naturally aspirated engine, which means a higher rpm limit will result in a lower torque figure in that type of engine. That's despite the engine doing the same amount of work, which explains why the horsepower rating was fairly consistent during three runs at around 183 hp. Torque varied from 143 pound-feet to as little as 125 lb-ft.
Secondly, the types of dynos measure power differently. The Mustang dyno used in the video takes aerodynamics and the vehicle's weight into account, while Dyno Jet units do not. The Dyno Jet dyno uses horsepower to run, which calls for a parasitic multiplier to create comparable performance figures. Fenske did this on the final run and the results were much different with 222 hp and 144 lb-ft of torque.
So, why might these numbers not be so significant? Every dyno is likely to spew out a different result. Ideally, for an owner to claim his or her car makes more horsepower than someone else's car, Jason says the cars would need to be tested on the same day, on the same dyno and with identical settings implemented. Skip bragging rights—the dyno is a helpful tool to help owners tune and compare how various aftermarket modifications improve a car's performance. Fenske will explain it in much greater detail above.