Track Results After 3.15 To 3.91 Swap

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Well finally got to gateway international raceway last night for the weekly test and tune ,(drag racing) after putting in my 3.91 differential here are the results before on my 3.15 i ran best time in 14.9 --96mph track conditions were optimal 60 degrees air temp 55 with my best 60 ft time ever 2.051
after the swap

r/t----.259
60'----2.142
330---6.136
1/8---9.467
mph--73.79
1000-12.345
1/4---14.748
mph---93.27 at this speed my car is @6700rpms in 4th gear (losing power)i tried switching to 5 th but my time dropped even more 14.989--92.95 ,,if i had a taller 4th gear i would be hitting a lot better times i lost some much speed because my car is running out of power at that rpm and lose so much time shifting to 5th ,,,,i think what im going to do is put a taller tire in the rear end i currently run 35 series tires but will now put on a 55 series tire

i will let you guys know times next track day with the larger tires

by the way getting to that speed is kickass :buttrock except for all the shifting

if anybody has any comments of how to over come this problem at 93mph im listenning thanks,tony

Welcome to the 3.91 club. What size tires are you running? Run a stock 15" wheel with a 255/50 BFG DR. Should drop that 60ft down into the 1.9x range and give you a little more mph in 4th as well. I can smell 14.3's from here.

Do you have a chip? M3 cams should be in your future too.

Wow that's weird how you lost 3 mph in the trap, i guess when you're redlining 4th and you can't get to 5th that's what happens.

tracks have turns

lol jp,
Soak your head.

Fitting the taller tyres will give you better gearing for your setup. If you post your redline, rear tyre size and gearbox ratios I can do a quick analysis for you on your optimum setup for drag racing (in terms of total gearing).

3.91 gearing 225/45r17 tires 7000 redline ,starts losing power @ 6500 at least in my car ,speed in 4th gear at 6900 rpm is like 95 mph ,(pretty accurate guess)