A transmission multiplies torque. If your engine outputs 200 torque at x rpm, in first gear the number will be dramatically higher than that at the wheels -- this is okay because the power in the rotational system does not change, just the torque due to the difference in rotating velocity (rpm). Given that the torque at the wheels is NOT the number you get on your dyno, the dyno needs the tach signal (for rpm) to calculate back to it given the engine output shaft velocity. The idea on the dyno is you want the gear that ends up being closest to 1:1 that allows you to see enough granularity on the dyno. IF you use a gear that's too low, say 2nd, you will fly through the rpm span and not collect very granular data, not to mention there will be more loss (lower numbers) than in 3rd or 4th. 3rd or 4th is the best gear because it has the least amount of loss -- additionally, you want to load your motor somewhat so you can see if it will knock or not.
black '03 rsx type-s ] [
274 whp @ 9psi jackson racing supercharged / alcohol injection ]
Last edited by Razathorn; 05-08-2006 at 12:34 PM.