gear ratio's, torque, dyno's,

[WhiteSx]

Hey all,

having done some research and study, i know that;

*when torque is applied to a gear ratio (above 1), the torque is multiplied.
*rwd inline gearbox 4th gear is 1:1 ratio due to input shaft locking to output shaft, tranverse(FWD) gearbox rarely have 1:1 ratio.

now my question is, has anyone done any back to back dyno's where they have had their engine dyno'd and then installed into car and done a chassis dyno run. too see what the differences are.

also does anyone take into account diff ratio's when looking at dyno figures (chassis dyno)? the reason i ask is that some cars run 3.9* compared to say a 4.7* diff ratio and this will affect torque at the wheels. the car with a higher diff ratio should pull a higher number but by how much? is it too small to even care about?

yes i know chassis dyno's are best for tuning but curiosity has got me in terms of power readings.

cheers

Dave

[AL510]

Hi Dave, horse power on a chassis dyno is calculated from tractive effort. if you reduce your gearing with a lower gear or rear ratio you increase your torque at the wheels but you reduce the rpm that you are turning them so the calculation works out the same in theory.
in my experience on chassis dynos it actually has a negative effect on your power output.
if you run in a higher gear it has always given a higher power out put which i have had it explained to me as the dynos rollers has a certain amount of weight that when excellerated has a certain amount of momentum. if you increase the excelleration by increasing your speed or by reducing the ramp time it tricks the dyno into thinking you have more power.that is why when you go to a dyno you should run the same wheels,and pressure and run in the same gear every time.

cheers, Al.