HP vs gear

[efnfast]

So, in round numbers.... if in fourth gear, 1:1 ratio, I dyno at 400 hp, if first gear is .5:1 do I effectively get 800 hp to the rear wheels?

[mike100]

hp is derived from torque so since the gear multiplies torque, 5 times, but the speed is 5 times slower, the hp should be the same.

I think you knew that, but there is some discussion of 3rd gear vs 4th gear dyno pulls and there is sometimes a few hp difference depending on drivetrain friction or dyno operation. I can't explain it, but it does skew a couple of percent depending.

[Hib Halverson]

Originally Posted by mike100

hp is derived from torque so since the gear multiplies torque, 5 times, but the speed is 5 times slower, the hp should be the same.
(snip)

The above is generally correct but you have to subtract any parasitic loss.

As for running in third or any gear other than direct drive, the hp is usually a little less because reduction or overdrive gears have slightly more loss in the transmission.