Questions regarding a mod I'd like to do (4.08:1)
 

I've been thinking over the past few months since I purchased my Z, that I'd like to do a cost effective mod to add a few or 35 hp. The most cost effective mod I've seen so far would be a final drive upgrade. Specifically, I'm thinking about replacing the stock 3.5:1 with a 4.08:1 which would be purchased here.

Anyone experienced with this kind of mod that can shed some light on the subject? How easily could a mechanic who doesn't know what he's doing F up my ride attempting a mod like this? How much could I expect to spend on labor? Is the transmission easily accessible in the Z? Or would the mechanic have to tear the thing apart to get to it...

15% more acceleration for $500 is unbeatable. Of course, my FE is going to go to ****, but that's the trade off I guess. I'm ok with that.

Thanks,

Mod

Thats a nice mod, i would do it. GEARS FTW!!!!

I have the 3.9, as thats what was popular at the time but the 4.081 seems to be the new popular fd. I don't know where your located but take it to a shop you can trust and everything should be fine. It's quite an improvement. If you have a base model it would be a good idea to get an lsd at the same time as they have to be installed together. Labor costs will vary look around here for shops in your area and get an estimate. Also just an fyi the final driver ring and pinion goes in the differential not the transmission.


My fuel economy around town didn't go down very much as you can go a gear higher in most cases but highway mileage will go down of course.

I was quoted $240 from ToyBoxAuto. Which, at their prices is around 3-4 hours worth of work. Im sure its a bit more involved than your average solid axle gear swap but I cant imagine it would be much more complicated. Ive only had my Z for a couple weeks now, so I havent really had the opportunity yet to get under there and tinker around at all. Just call ToyBoxAuto, and ask for Rich. He's a cool guy, Im sure he'll give you the 5 minute version of what needs to be done.

By the way when I was talking to Rich he said the fuel economy didnt change by more than roughly 2 mpg. In my opinion, well worth the improvement.

lol I knew that... brain fart. Won't be doing this myself thankfully. :icon17:

There's a guy in my area that has a 4:12 his car goes through gears fast as SHlT. I want to do this mod BAD!

There's a great sticky at the top of this forum dedicated to this mod... Mod can delete this thread if you want. Sorry for not checking first.

p.s. thanks for the encouragement every1

LOLOLOL

I love how those guys couldn't even take the time to write their OWN product description, they had to steal mine (used my picture too, but that is far less offensive)

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

Modulus, what part of CT are you from?

haha he did...wow.

And what the hell is toy box auto?

lol - the name just opens itself up to all sorts of interpretation doesn't it lolol

lawsuit Z1! lol

in the process of getting this done with nismo lsd.. like everyone has been saying this is probably the best mod you can do n/a. and also this wont give you 35hp. just quicker through the gears which= faster acceleration.

anyone know of any shops in nj tat would do this mod?

Yep.... Think im gonna do this.

Just because you increase gearing by 15% doesn't mean you increase acceleration by 15%..............it is more like the cube root [little less than cube more like 2.5 root] of the 15% more like 2.5% time wise.

A 15% increase in rear wheel torque via gear multiplication can however decrease quarter mile by 0.2-0.3 seconds if you don't loose time by shifting to another gear [shift time loss vs acceleration gained].

We've had a few Q45 [stock 3.538 diff] do these 4.083 conversions. The major change has been the 10-12% decline in highway MPG.

Also you won't see a measured 15% increase in wheel torque because the higher ratio increases the frictional losses in differential by about 0.5-1%

you're splitting hairs in a major way

Perhaps that larger decline in gas mileage has to do with it being a far heavier car, with an auto transmission, and an already thirst v8

On the Z, the change in mileage is negliable at best. I've had the 3.9 on my car for years now...more years with it, than without it in fact, and my mileage has stayed exactly the same as when the car had the std. rear in it. I am sure those with a 4.08 can comment on their mileage changes directly.

I have the 4.08 gears in and I could not notice a diffence in Mileage..... I also don't run around at 80mph everywhere either... b/c at 80 mph your at about 3500 rpms. But I'm usually the guy thats going 60 or 65 on the highway.... unless provoked by someone haha.

Agreed. In my Cobra, I went from factory 3.27s to 4.10s. Loss of fuel economy was not much at all. After I got used to the gears, I didn't really notice a difference. In town, you could see an improvement.

I went from 3.3 to 3.7 in an AT G... mpg did suffer, but not enough for me to care... most people that do a performance mod are willing to sacrifice mpg anyway (otherwise, keep it stock - you won’t get better mpg than that).