Thumper Posted December 18, 2004 Share Posted December 18, 2004 Well my rear differential has been making noise for awhile now and tonight it went boom. So I am faced with buying a junkyard rear diff. I unfortantely do not have the money for the 3.7lsd so I will be buying either a 3.545 or a 3.9. I will also be installing a 280zx NA 5-spd tranny. So with this gear ration and an estimate qt time of 12.9 @ 105mph. What rear end would you run. My tires are 225/50/r15 on stock rims but one day will be upgraded to 245/50/r15. TIA Ted Quote Link to comment Share on other sites More sharing options...
datsunlover Posted December 18, 2004 Share Posted December 18, 2004 My choise would be the 3.90 and IIRC, that's what came in all the zx's with the 5 gear. I'm going to be doing the same swap in my 75 (my 3.54 is shot, and the stock 4 gear is.. useless. Grinding, and a terible 'drop' between 2nd +3rd shifts.) From what I've heard, the 82+ zx 5 gear has WAY better ratios, and a decent 5th.. Part of the reason they switched to a 3.90 (the zx is HEAVY..there's the main reason..) I believe, is to get better acceleration. Obviously, the car would be really rev happy with the 4 gear throught a 3.9, hence the change to 5 speed. What do you have right now, a 3.54? Quote Link to comment Share on other sites More sharing options...
Thumper Posted December 18, 2004 Author Share Posted December 18, 2004 Right now I have a 3.545. I can get a 3.9 or a 3.545 for the same price. I am leaning towards another 3.545 so that I can stay in each gear longer and hold the boost. And the 3.9 gear will put me near my redline in 4th gear in the qt mile. On the other hand it will increase torque to the wheels by 11%. Anyother suggestions? TIA Quote Link to comment Share on other sites More sharing options...
Clifton Posted December 18, 2004 Share Posted December 18, 2004 My choise would be the 3.90 and IIRC, that's what came in all the zx's with the 5 gear. Only the later, I belive 81+ have the 3.9. There is a trans ratio change along with the diff ratio change. I run a 3.9 and a 3.7. I will soon change the 3.7 to a 3.9 too. If you are concerned with your highway rpm's get the later 5spd along with the 3.9. 5th is .75 compared to the earlier .86. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted December 18, 2004 Share Posted December 18, 2004 My '80 parts car with T-tops came with a 3.90. Quote Link to comment Share on other sites More sharing options...
Drax240z Posted December 19, 2004 Share Posted December 19, 2004 Way back when in this forum, someone did a back to back comparison in the 1/4 mile between a 3.90 setup in a turbo car, and a 3.54 setup. The 3.54 was quite a bit faster. Many others chimed in that they found the same with their cars. I put a 3.54:1 in my turbo car, and allready have enough torque in 1st and 2nd that traction is a real issue. With a 3.90 that problem would be worse, and I'd also have to shift sooner. Even as far as autocross goes, I am able to leave corners at the bottom of 2nd gear and the car pulls well from low rpm in 2nd gear with the 3.54. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.