3.9 upgrade worth it, dedicated track car?
 

My car is in the shop right now getting transmission and a new Tomei LSD. Its pretty expensive as it is with just this right now. Will the extra 1000 or so for a 3.9 upgrade be worth it? How about effects on SRM. Any track guys with info

Mike, I have 3.9 with 677mm tall tyre *275/40R18) for road use and SRM still works a treat .... 4.08:1 is noticeably out though ........

I will go to 4.08:1 diff with new engine and Quaife box on short tracks and still use the 3.9 on longer tracks. Engine and box should be in the car by March.

3.9 with 1:1 top gear and 280/655R18 slick @ 8500rpm is 272kph
4.08 with 1:1 top gear and same tyre @ 8500rpm is 260kph

Difference between 3.7 and 3.9 pulling out of turns can definable be felt, acceleration with 4.08 is proportionately better but with OEM rev-limit (still have std oil pump), you run out of revs with 4.08 and my little (650mm diameter) R-Spec tyres

I have the 3.9 and if I were to do it again, I would go with the 4.08 gears...if not 4.36. With EcuTek, you can get the new gear ratios programmed in for SRM and mine is spot-on.

decided on the 4.08. Ill just have to heel toe until uprev fixes it. They say they are working on it. This car has just made me lazy. I have been running 295/40-18s which are much taller than stock, but I am just about out of stock of those.