Why does my dyno plot look “flatter” than the dyno plot Ive seen from chassis dynos for my car?
This is primarily due to aerodynamic drag on your vehicle. The amount of horsepower that is spent overcoming aerodynamic drag is proportional to the cube of the vehicle velocity. In other words, you use 8 times as much horsepower just to overcome aerodynamic drag when your velocity doubles. For example, if aerodynamic drag robs your vehicle of 3 HP at 25 MPH, it will be robbed of 24 HP at 50 MPH… the velocity doubles, but the aero drag loss goes up by a factor of 8! So even though you are usually generating more horsepower at higher RPMs in a particular gear, you are also going faster, and the horsepower needed to overcome aerodynamic drag is much higher at the upper end of the RPM range. This increasing “negative horsepower” due to aero drag is largely cancelling out the increased horsepower generated by the engine.
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