diff

[s.hogan3]

in my 400 the diff is a 3.31 ive been told that i can use a jag v12 xjs diff at 2.88 or try and get a jag e type on at 3.07 but these are rear is there anyone here brainy to work out say at 40 miles a hour wote the revs wil be in each gear so i can work out which diff will match the engine speek as the 3.31 is far to low
thanks steve

[Wedg1e]

Aye, it's easy enough. Start by finding the gearbox ratios. Then divide the engine speed by that figure e.g 5th might be 0.88:1, so at 6000 engine rpm the propshaft would be doing 5280 rpm.
Then divide that by whatever diff ratio you fancy, say 3.08 - giving 1714rpm at the driveshafts/ wheels.
Find out the rolling circumference of the wheels (inches), multiply by 1714 rpm and that'll be the number of inches per minute that the wheels travel; divide by 1056 to get MPH

[rev-erend]

s.hogan3 said:

in my 400 the diff is a 3.31 ive been told that i can use a jag v12 xjs diff at 2.88 or try and get a jag e type on at 3.07 but these are rear is there anyone here brainy to work out say at 40 miles a hour wote the revs wil be in each gear so i can work out which diff will match the engine speek as the 3.31 is far to low
thanks steve

Those diff's would have the effect of making the acceleration slower.. rev's would be lower when cruising too.

You could call someone like Hardy Eng - would would probably be able to just change the crown wheel and pinion to these other ratios for you.

[adam quantrill]

Hi Steve - are you saying that the 3.31 is too low - so you need a higher ratio?

This would make sense if you've improved the engine power delivery.

[shpub]

Theres a spreadsheet on www.tvrbooks.co.uk that will calculate all this for different wheel/tyres/gearbox/diff combinations. In the tyres FAQ if I remember correctly.

[adam quantrill]

Cheers Steve very useful, can now be had here:

Spreadsheet