This might help you ,
" BA XR6 diff ratios ?
Hey , can anyone tell me what the standard diff ratio is on a Ba XR6 auto ? - i want to get more grunt off a standing start but dont want to go to the expense of fitting a turbo etc... I once read ( in a ford magazine) about a maths formula expressed as a percentage of improvement eg; 3.45 diff to a 3.77 diff = 10% which means 10% higher revs for the same speed in each gear - 10% quicker off the standing start - 10% more fuel usage etc etc etc.... has anyone change diff ratios and what affect did it have on performance ??????
" i had 3.73's in it as i had it converted to manual and was very fun, but when i converted back to auto i found the 3.73's were very lame.... almost felt stock. I think revs were 2100rpm @ 100kph
so in went 4.11 LSD, and it certainly felt alot more zippier off the mark but still not as short geared as a manual with 3.45 diff. Revs are 2300rpm, @ 100kph.......doesnt rev that high at all really. First gear in the e-series auto's is very tall... i think its 2.36 or something i forget, but 4.11's are needed to help overcome this. With your b-series im not sure if the ratio's changed with the autos?
heres a useful calculator you can use to work out rpm's VS any gear & diff ratio. All you need is your gearbox ratio's and you can input any diff ratio and speed etc. to see how it effects rpm's
MOTOR - A Rear Axle Calculator
and yes theres more traction problems but the lsd helps alot...... even when the tyres are spinning and the car leaves the mark sideways, its still going faster than the 3.73's with full traction if that makes sense. "
" Go with 3.9:1 or 4.1:1 if you're an automatic.
If manual, probably no need for any higher than a 3.7:1.
You won't gain any KW from it, but your acceleration will be a sh*t load quicker. Will feel like the car is jumping off the line if you stall it up. "