hey guys I have been looking into changing out the gears on my 05 5AT z and i have been able to find some information in old threads, but a lot of the threads i found were more for the 6MT. So my question is this...it seems like the most common answer i have seen people is getting is that the 3.9 gears are the best choice for a NA 5AT and the 4.08 gears are what a lot of people are doing for the NA 6MT but just I have yet to see anyone with 4.08s and a reflash to raise the rev limiter on a 5AT. Has this been done or would this setup just be too much for a streetable 5AT z? That being said I think i am going to get the pumpkin from a 6MT and go with the 3.9 gears and a reflash sometime soon.

 

I'd go with 3.7
Def don't go higher than 3.9 on a DD

 

I am not a fan of changing the final drive for the street for practical reasons. You can calculate MPH and speed here. See what best suits your needs.

http://www.wallaceracing.com/Calculators.htm

 

thanks...im definitely going to go with the 3.9 but just out of curiousity has anyone with the 5AT ever gone with the 4.08 gears? i have not found one that has yet, probably because of how terrible it would be as a DD with those short gears

 

youuuuuuuuu should probably go with the 3.7's sir. There's a reason that 4.08's aren't popular on DD 5ATs, and 3.9 is really pushing it.

 

just out of curiosity do you have any experience with the 3.7 or the 3.9 gears?

 

The 5AT has longer gear ratios natively vs the 6MT. Use the calculator above and if the speeds look tolerable (mostly the highway cruising speed), then I'd say go for it. I've heard of others going for 3.9 in the past and reportedly it's been very much liked (ISMSolutions for one I think over on g35 driver).

 

here are all the speeds, from the sticky thread in this section, for a Z/G, saves you the work of inputting #'s

https://my350z.com/forum/4390297-post1.html

 

^ Those gear ratios are for a 6MT?

 

alright thanks everyone...ive decided im going to go with the 3.9 gears with a MT pumpkin and a reflash to raise the rev limiter

 

Hey man i just changed the gears on my car from a 3.5 FD to a 4.0FD on my AT Z. I dont really see any problem with it at all, it does tend to keep the revs higher when cruising on the highway but nothing abnormal. If you are interested hit me up and I can guide you with any questions that you need, also I have installed the Transgo kit and a Osiris flash with the rev limiter raised.

 

hey guys, to use the 3.5 final gear on the 5AT, do i need to find a 6mt pumpkin?

 

you need a 6MT differential

 

Am not sure if you need the pumpkin man, but we I installed the 4.0 gears I needed it for mine because it did not fit with the 5at one. I could be wrong if anyone knows better, You can ask 'Coach' here in the forums he helped me alot also.

 

3.692 (3.7) here - very streetable, notable increase in acceleration, fun for moderate track.


the 5AT 3.3 gear is thicker than the rest... anything shorter than 3.3 will require MT diff (OEM or aftermarket) - that's the only thing that doesnt allow the gear to fit.

 

Good time to upgrade the LSD!

 

Can he use the pumpkin from the 5at with a 3.5 diff?

 

again, he needs a MT Differential....

there is no difference between the pumpkin housings...only the internals

 

So... if he gets a M/T pumpkin to swap in, it would typically have the MT differential and thus the 3.5 final? For example if he were to get one from a junkyard or something?

 

yep, that's what most people do (that go with 3.5)... you can also use the pumpkin from 07+ G35 sedan or G37/370Z for 3.7 (is not as direct swap as 3.5, but it's doable, there are DIY on driver, probably here too somewhere).

The only reason to use you existing pumpkin is of you plan to use after market diff (I put 3.7 with Quaife in my OEM pumpkin)