Stock Yaris as fast as stock 1982 Z28 Camaro/Trans Am!!

[Yaris Hilton]

Hale's formula doesn't take into account the shape of the power curve. It works well when comparing similar cars, which should have similarly shaped power curves, but average horsepower over the distance is what produces the top end speed. That's a result of average acceleration over the distance.

[427chev]

Originally Posted by Yaris Hilton

Hale's formula doesn't take into account the shape of the power curve. It works well when comparing similar cars, which should have similarly shaped power curves, but average horsepower over the distance is what produces the top end speed. That's a result of average acceleration over the distance.

As illustrated below, the formula works quite well when actual trap speed results are compared against published peak SAE NET peak power figures (preferably Certified SAE NET) - regardless of engine type. If it doesn't then the power rating itself is suspicious [e.g. BMW 335i, which produces more than the claimed (but not SAE certified] 300 HP.

Example 1: Few modern performance passenger car engines are as peaky (and produce less torque) than the Honda S2000's 2.2 liter DOHC 4 cylinder:

http://www.caranddriver.com/reviews/...cs+page-2.html

Curb weight (car with a full tank of gas) is 2,792 pounds, so we'll figure an even 3,000 pounds with a driver and test equipment added. Trap speed was 99 MPH.

Peak Engine HP = (99/234)^3 * 3,000 pounds = 227 HP. Honda rates it at 237 SAE Certified SAE NET HP


Example 2: This new Corvette features a 6.2 liter V8 that offers a very differently shaped power curve (and far more torque) than the Honda S2000's high revving 4 cylinder. Curb weight is 3,299 pounds, so we'll figure an even 3,500 pounds with driver and test equipment. Trap speed was 116 MPH.

http://www.caranddriver.com/content/..._z51_08_ss.pdf

Peak Engine HP = (116/234)^3 * 3,500 pounds = 426 HP. Chevrolet rates it as 436 SAE Certified SAE NET HP.


That phenomenon is attributable to the affect that gearing has on drivewheel torque, relative to vehicle speed. Your point would be more valid if cars didn't use transmissions, but they do. Note: The formula doesn't work as well for large trucks (due to big tires and lots of aero drag) nor was it intended to.