I have a 1999 ///M Roadster. I have searched the Z3 and Z3 coupe message board and can not find an answer to my questions about a performance differential for my little roadster.
I hope you guys with the ///M3 can help me out. I'm also comming to you because the ///M3 has been around longer and your message board has more tech. information then most.
I think I can switch to a 3:45 3:64 or 3:73 differential. I think the 3:73 is more then what I'm looking for.
The 3:64 will make my car top out at just about the cutout limits of 136mph. I have been told it will do close to 150mph without the cutouts. Since I want to get there faster, more then simply drive fast, lowering the top end a bit is ok with me. I am willing to trade top end for acceleration.
I understand that the shift points will be about 3mph lower in 1st, 5mph lower in 2ed, 8mph lower in 3ed, 11 mph lower in 4th with the 3:64 gearing shifting at 5,500rpm. (Yes, I know it goes to 6,500rpm or 7,000rpm.)
I want to know if any of you have any experiance changing the rear end differentials in your ///M3 and how it effected the performance and wheather you thought this was a good performance investment.
(I'm not worried about gas useage.)
I do wonder what it will be like at 80mph, doing close to 4,000rpm on the freeway? Any Comments?
I also wonder about the 40% lockup as a opposed to the factory 25% lockup? Any comments?
I also autocross a little. (I will do five this year.) How will the new differential effect me point wise? I think it will help me get out of the corner faster by allowing higher rpms (In a better torque power range.) at lower second gear speeds.
If I did the differential, besides a Jim C chip and air intake, what other ideas do you have for me.