I have a carbonetics lsd that I bought from forged performance. I track my car and push to the limits as best i can. I occasionally drive my z on the street as well. Agree with comments that it is very street'able. And the performance at the track is night and day. I can roll on the gas mid-corner and I get predictable response and better hookup every single time. Agree with the comment that anyone adding HP through SC or whatever, or anyone taking weight off, is going to need a rear diff. A real one. In fact, I'd go so far as to say that a carbonetics rear diff should prob be the FIRST MOD you do when you get this car! Finally, you don't have to run the expensive carbonetics gear oil... I've talked with several folks that run this instead. I use it. Just make sure you use the thicker version of motul gear oil and there won't be any noise from the diff.

http://d5otzd52uv6zz.cloudfront.net/...fd29d5-350.jpg

I've been thinking about this. Drag racers like a bigger final drive gear (http://www.the370z.com/engine-drivet...-9-4-08-a.html). I think for road courses it is better to shift less often and on the tracks I run I find myself shifting near the end of a straight b/c I need another 5-10 mph out of 2nd and 3rd. So for me, perhaps a lower 3.3:1 final drive ratio. In my car, that would bring 2nd gear at redline from 69mph to 77 and 3rd gear from 99mph to 111. The risk would be not having enough torque for low speed 2nd gear work in a slow hairpin... but then there's 1st gear!

So it really depends on what you're trying to do. If you want to drag race, go with a bigger gear and improve your 1/4 mile. Otherwise leave it alone or go with a smaller gear even.