changing final drive ratio question

[barryogen]

Just some thoughts on this please. Just humour me if you will

If I drop ~500kg from the 1200kg car, and did an engine swap(and all that entails) to one producing ~2x as much torque, could I get away with changing the final drive to make it have a bit taller, so higher top speed?

the sort of change I was looking at was going from 4.111 to 4.444

The reason I was thinking of doing this is that there is little need for the lower gearing as the replacement engine has considerably more torque availible right through the rev range, and also the weight of the vehicle has dropped considerably.

[wde_bdy]

You are going the wrong way with your diff ratio, if you have 4.1 you need to go up to 3.7 to get higher top speed. It works like this, pinion has say 10 teeth and the crownwheel 41 so C/P is 41/10 or 4.1. This means the gearbox output spins 4.1 time for one turn of the axle. 3.7 diff will give 3.7 revolutions of gearbox output for 1 revolution of the axle so less engine revs for same speed or more speed for same engine revs.
Yes, if you have more torque it should be no problem to gear the car up for a higher top speed.

Callum

[barryogen]

You are going the wrong way with your diff ratio, if you have 4.1 you need to go up to 3.7 to get higher top speed.

haha, sorry, thats what I meant(4.444 to 4.111).

Yes, if you have more torque it should be no problem to gear the car up for a higher top speed.

thanks.