Was just thinking this today, a chassis dyno measures wheel torque and converts it into hp using the formula of TQ*engine speed / 5252 = HP.

Say for example 2 identical engines were run, both had a confirmed 200fwhp, lets say one had a 4.4 final drive and one had a 4.9 final drive and assume all gears 1-5 were ratio'd the same.

Both cars are run in 4th gear. Now as the 4.9 FD car has shorter gearing(due to the FD) this will obviously show and increase in wheel torque. Correct?
So assuming torque at wheels is shown to increase on the 4.9 equipped car, would it stand to reason that a chassis dyno would read a higher whp figure for it compared to the 4.4 equipped car?

Thoughts please

 

It has been my experience that the shorter gearing does show its mechanical advantage on the dyno.

 

This is one of the many reasons not to get too hung up on the size of the numbers.An experienced operator can bias the numbers high or low.For the dyno to be useful you need to be aware of what can very your results.Chassis dynos measure acceleration as much as hp/tq.Tire pressures,widths,weights can all effect numbers.With the bike dynos we use we try to use a gearing selection that gets as close to 1:1 as possible.Pulls in different gears will result in different numbers.Engine dynos (crankshaft) eliminate these variables but create a whole new set of variables.