im just about to send the diff away.....and cant decide on 4.4 or 4.7....how accurate are the online calculators?
diameter of tyres are 21.5 in.....is there any sums i can do?
using 6 speed 8 box....with the 4.1 hooking 5th 3 times round combe but still got plenty of revs but still plenty of work to do in corner exit speed.
6th gear waste of time?
4.7 give Vmax of 125.
4.4 gives Vmax of 133.
6th is ratio 0.83 so if it does top out up to avon rise in 5th theres always 6th
A stock Rx8 on a 4.4:1 diff with 658 mm diameter tyres runs out of power at a shade under 150 mph. You\'re in 5th and you still have a few rpm to pull before the limiter, 6th gear adds no speed on the flat.
21.5" tyres are 548.25 mm diameter. This would be at 125 mph in 5th at the same rpm that the RX8 is at 150 mph. You could probably go to 4.7:1 and still have speed to spare as that would put you at 117 mph in 5th at the same rpm. There are a few more things to consider over and above that, stuff that it\'s harder to predict without knowing corner speeds and the like but I don\'t think you\'ll run out of rpm with 4.7:1 diff at Combe. I\'ve been there in my 8 a few times and I\'ve never got out of 4th gear, in fact I\'m only in 3rd and 4th at Combe in the 8, I\'m on the beep in 4th at the top of Avon rise and then in 3rd for Quarry. I only use 2nd there if I get slowed in the chicanes by other traffic. I would be nice to be going from 4th to 5th as they\'re closer ratios than 3rd and 4th and you\'re into the power quicker.
Cheers Will! 4.7 it is...should make for some rapid acceleration as well.
Just a consideration to make with diff ratio is that the higher you go 4.7 etc your pinion has less teeth and doing a lot of track time can cause a lot of heat, maybe worth a diff cooler to prolong your diff oils life and your diff?
yes good call Grant! will do some research...pretty much re-engineered the whole car now...infact i think ive had to address all areas!