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

[GeneW]

Originally Posted by 427chev

Differences in gearing and traction could significantly alter ET (time to distance), though Trap Speed (speed to distance) would remain relatively unchanged. It is for that reason that Trap Speed (along with vehicle weight) provides such a good estimate of actual peak engine horsepower.

Hale's Formula (as used by the Moroso Power/Speed Calculator):

Peak Flywheel HP = (1/4 mile Trap Speed/234)^3 * Race Weight

Example.

A stick shift, bone stock Yaris 2 door hatch traps @ roughly 81 MPH and weighs ~ 2,500 pounds with a driver and a full tank of gas

(81 MPH/234)^3 * 2,500 pounds = 103.69 peak flywheel HP

Toyota rates the Yaris @ 106 peak flywheel HP (SAE certified).

I'd call that pretty close.

I'd agree that the formula is within a reasonable variation about two percent difference. Close enough for "Government Work" as we used to say.

Originally Posted by 427chev

The formula seemingly doesn't "work" with pre-1972 model year American cars because those published figures (SAE Gross) were essentially meaningless. Similarly some non-SAE certified SAE net figures may also be less than truthful, though far less so than the old SAE Gross figures. In either case, Hale's formula gives an excellent approximation of TRUE "as installed" peak engine HP.

I recall hearing this story myself but I'm unclear about the circumstances. I've heard histories and opinions about it in the past but I'm unclear myself about when HP calculations and measurement standards were changed, but I have heard that they were changed.

Gene