Dont get any gears for the Z. I had 4.08 in mine for about 2 month with a Nismo Lsd and it was terrible. It made a car that doest get any traction to a even worse tire smoker. 1st and 2nd become totally useless...unless u drive around with drag slicks. Also even with the 3.9 my friend on the highway at 60mph is at around 3300 rpm compared to about 2400...just forget about driving around on the highway at 75-80mph.

Also ive raced a bunch of Z's with 3.9's and 4.08's and I can still beat them. It really doesnt make the car that much faster. The car already has a pretty agressive gear in it. (manual cars only)

Only bolt-ons that make a difference in these cars is..

5/16 spacer (Motordyne only!!)
re-flash
Test pipes.
y-pipe.
Pop charger or K&N drop-in (No CAI's)

Thats it.

U can even keep the stock exhaust. You wont lose any power keeping it on. If u want bang for the buck get the spacer and the test pipes and it will feel like a different car.
After my test pipes and spacer WOT runs from 80-140 were insane compared to stock where it would just crawl up to speed.

The Z with CORRECT bolt-ons can become a very fun car compared to stock. People have the bolt-ons down to a science for these cars, if u study my350z.com u will see what it takes exactly to make more power out of your NA setup. Dont experiment with mods that dont work. U will become frustrated because the car wont get any faster at all.

When my Z was stock I couldnt beat anybody in any race, now correctly modded I can hang with the best of them, M3's, GT's, turbo cars.. They all think im seceretly running Nos, I tell them I have a couple of bolt-ons and they cant believe it.