Yes I searched, I've seen the post with all the topout speeds and whatnot, but I wanted to get opinions from people with both. The 4.083 is way cheaper on MyNismo, I've only seen the 3.917 on 350Evo ($750) and MyNismo (1k+). I guess the 3.917 is much harder to order.

So given that, is the less than .1 difference in ratio going to make any noticable difference? I've got an 05 (non-HR) which I plan on keeping NA as a DD for the foreseeable future. I don't want to increase drag times but I do want that torque/***-glued-to-seat feeling for daily driving fun. I also don't plan on flashing anytime soon, though I'd really like too. Between flash, clutch/flywheel, and the final drive I figured the gear ratio increase would give me the most enjoyment for the money.

 

Yes, there is a noticeable difference. If I recall correctly, the change to 3.917 is roughly a 10% gearing difference from stock [MT], and the 4.083 is about 15%.

 

No reason not to purchase the 4.083s. 15% faster acceleration, more aggressive.

Get the 4.083s. You'll love them. I know I do.

 

What kind of RPMs are you "turning", at around 80 mph??

 

Hovering at 3100rpms at 80. I don't see any differences in my fuel efficiency.

After all if you're thinking about performance modifications, MPG should be lower on the list.

For the first few months you might see a drastic change in MPG, that will be from the heavy foot that just can't get enough of the 4.083's.

 

Ok so I'm pretty sold on the 4.083 considering the price and performance. Now here's another question, what kind of place should I be looking for to break open my diff and install it correctly? I'm wary of taking it to the dealership for that.

 

That's really not too bad!
...and I bet it's fun!

Also, how is your acceleration off the line? Is it noticeably better??

 

Do it yourself??

 

probably a bad idea unless you've done that kind of thing before. Ya need the right size shims, and all the tools and knowledge to know which ones to put in. If not shops are in your area you could always try a dealer...labor would suck though. What area are you in? Sometimes you could go to a tech school and have your car be a guinea pig for a demo in class.

 

yeah, id be less worried about the dealer screwing it up and more about the butthole love they would give you for it

 

My 4.08 puts me at 3400rpm at 80mph. Maybe my rpm's are a little higher because I'm also running 285/30/19 in the rear which is lower profile than stock.

 

I put the LSD in my Z. By the time I was done, it cost about $300 in special tools and equipment. I really did enjoy it, but I may as well have paid someone.

Take it to a transmission shop. They're the most experienced at this type of work.

 

Me too! I really enjoy this type of work...therapy!!

 

i love my 3.9s, im selling my car or else i would switch to the 4.083s just to see what the fuzzz is about btw anyone want to do a swap of pumpkins with mine? plus say 300 bucks? car will be traded in or sold within a week or two.......

 

First, what year is the car?

If the car is an 03-06, a flash, or some means of increasing the rev limiter should go hand and hand with the ring and pinion swap. If the car is an 07 and up, which has the higher rev limiter from the factory, this is not essential.

This is not a DIY type of install either unless you've got alot of experience and alot of patience

3.9 final drive: http://www.z1auto.com/prodmore.asp?m...ne&prodid=1726

4.08 final drive: http://www.z1auto.com/prodmore.asp?m...ne&prodid=2833

Since I know the question will come up, there is zero difference between the Central 20, the 350Evo, and the NISMO 3.9 final drive...all are factory Nissan parts, simply rebadged/branded. We used to heavily stock the 3.9, but since the 4.08 is a bit more readily available, and a bit less expensive, we now keep them on the shelf, ready to go

 

Adam & all,
which would work "best" for an Auto. Trans.??

 

I can't say as I have 0 experience with auto's

 

The auto tranny has a 3.3 fd gear. So I would recommend the 3.9 or maybe even the 3.7

Lots of auto guys trade with manual guys who are turbo'd, because the manual turbo guys want longer gears for their boost and the auto guys are happy to get a 3.3---->3.5

 

I think that I read on this site that the 3.7 works best for the auto. That is what is in the G37 coupe and also the GT-R

 

Yes it's an 05 and I really can't afford the gear, install, AND flash all at once. I may just have to postpone this mod as the install is going to be more expensive than I had figured and I know I'm going to want the reflash when I'm running out of RPMs. Thanks for the info and I'll probably buy it thru Z1 when I do, I like the kit options.