In Reply to: Performance Differential Assistance Requested. posted by Lester on October 08, 1999 at 00:16:43:
A rear diff is a poor mans supercharger. It is a great mod to do. With the 40% lockup you will get out of it, your rear tires will get better grip. THis makes the power apply more evenly to both wheels. If you are driving the car on the street and highways, I would recemend the 3.45 gear as it is a great all around gear. The 3.65 is a little high for highway use and the 3.73 is just about a pure race gear, unless you have a 6spd. I would get the diff though as it will greatly help you out in autocrossing and your enjoyment of the car.
: 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.