Ok i just called up BJ from 350evo and asked him all about putting in a 3.9 final drive in a automatic. He tells me it would work but hes not sure how streetable it will be. Im planning on getting the entire assembled unit with the 3.9 final drive and i even bought a 3.5 fd pumpkin for the core exchange. My question is does anybody have any experience in the 3.9 final drive for a automatic?? Im not sure how streetable it will be, i heard the 3.9 final drive makes a huge difference for the automatic compared to the 3.5 fd and i would much rather get the 3.9 fd. However, i use my car as a daily driver and i dont want anything too crazy and not streetable. Can anybody with experience with the 3.9 fd on a auto point me to the right direction?? Im willing to sacrifice a little bit of comfort for speed, as long as its not too out of hand. Also i was wondering if i was to drive on D and smash the gas after getting the 3.9 fd, would the computer be able to change the gears on its own quick enough before it hits the rev limiter?? I dont have a raised rev limiter. Thank You.

 

well your auto might not physically be able to shift fast enough in Drive mode. You'd have to get a feel for doing it in manual mode possibly.

I dunno, maybe it would be fast enough. A valve body upgrade wouldn't hurt of course.

traction might start to be an issue



no one really has done it except 1 or 2 people that i've heard of

 

with the 3.5 in my AT5 , redline cames veryyyyyyyy quick in first and second . I think the 3.5 is just about right , and is still streetable

 

So you guys suggest not to get the 3.9 final drive?? But all of this kinda just seems like pure speculation. Because none of us has actually used the 3.9 final drive before. Im still hoping i can get somebody that has experienced the 3.9 final drive and saying it is not streetable. And by not streetable, i mean the ride feeling very jerky or uncomfortable because the final drive makes you drive at such a high rpm at all times. And also i want to know if anybody with experience can comment that a 3.9 final drive definitely cannot be driven in D mode because if you floor the gas you will hit the rev limiter too quick for the computer to change the gear in time.

 

Well if no one had tried it yet...no one can comment . Go for it and be the first ! Alot of money to see if it works or not

 

Definitely interested.
cause my AT5 has 3.5 fd and APS TT kit (9PSI Boost)
Now I having a problem take off (Traction) 1 & 2
So now I. trying to change back to 3.3FD ...............?????????

 

do a 3.7...

 

With a TT setup, i think it would be best to run 3.3 Final Drive, since you have that much power, you want to stay in each gear as long as possible. But im running N/A, so 3.3 Fd wouldn't be good for me.



Theres a 3.7 FD?? Who sells it??

 

I can sell it...

 

Really?? Can you pm me with some info regarding the 3.7 FD?? Such as the cost, what it comes with and waht company makes it and etc?? I would definitely be interested in a 3.7 FD. Although im still thinkin about getting a 3.9 FD, but i only know of one person who has got this done before on a automatic and he isn't responding on my pmz.

 

NISSAN makes it...

there are a few options...

Well, only one...

You would have to run a NISMO LSD with it, or get an LSD and purchase the 3.5 stub axles etc that would work with that LSD... any LSD that works with the 3.5 / 3.7 / 3.9 will work... You can get a VLSD but, would cost more and doesnt come with the 3.7 assembly...

 

Well i already have a entire 3.5 fd pumpkin with vlsd. So that means i have everything to make this work right? What website can i go to ck up on this 3.7 FD??

 

I dont know of any others talking about using the 3.7...

You will need a new pumpkin though...

so if you already have the 3.5... stick with that... or go to the 3.9...

3.7 you will need a different pumpkin...

atleast that is what we did... Ill have to pull it and measure to see if it will fit in the standard 350Z pumpkin...

the pumpkin on all 350z Auto or Manual is the same... its only the gearing and other components that are different...

 

There are a few guys with 3.9's in their auto g35c over on g35driver.com. They said it killed the cruise control and dropped his mpg by 1 or 2. Never said if he could floor it in drive w/o bouncing off the rev limiter but does claim it dropped his ET by like 1.0 seconds I think whereas most people say the 3.5's only drop your ET's by like .2-.3 seconds.

 

Yea thats what i heard also, and i even pmed those guys from g35driver.com but haven't gotten a response from them. They never said anything about how streetable it was tho. All they talked about was the difference it makes performance wise and i already knew it was going to make a huge difference. Problem is this car is my daily driver, so i wanna know how it is in that aspect. I wonder if those g35driver ppl use it for daily driving or just for track use.

 

Jason,

Can you PM me with more info on the 3.7 AND 3.9 Options for my 5AT?

Thanks

 

+1

 

I would be interested in more info on a 3.7 FD. I have the 5AT with the 3.5 FD swap done. My 3.5 FD has the VLSD.

Jason,
How about posting info up here on EXACTLY what would be needed to do the 3.7 swap and if it would be possible with the existing 3.5 FD w/VLSD.


Just as an FYI, I shaved .3 sec off my 1/4 mile times with the 3.5 FD. I also trapped about 4 MPH faster after the swap!

 

Ok here are my calculations on the gears:


1st - 3.540
2nd - 2.264
3rd - 1.471
4th - 1.000
5th - 0.834


Stock Tire Size 245/45/18 = Revs Per Mile = 756

FD = 3.3
FD = 3.538
FD = 3.700
FD = 3.917


Formula:

RPM / FD Gear Size / Tire RPM x 60 = Speed in MPH


RPM:

3000 RPM in 4th Gear:

3.3 @ 3000 RPM = 72.15 MPH
3.538 @ 3000 RPM = 67.29 MPH
3.700 @ 3000 RPM = 64.35 MPH
3.917 @ 3000 RPM = 60.78 MPH

3.3 @ 6000 RPM = 144.30 MPH
3.538 @ 6000 RPM = 134.59 MPH
3.700 @ 6000 RPM = 128.70 MPH
3.917 @ 6000 RPM = 121.57 MPH

Forumla for other gears:

RPM / (FD Gear Size x Tranny Gear Size) / Tire RPM x 60 = Speed in MPH


3000 RPM in 5th Gear:

3.3 @ 3000 RPM = 86.51 MPH
3.538 @ 3000 RPM = 80.71 MPH
3.700 @ 3000 RPM = 77.17 MPH
3.917 @ 3000 RPM = 72.90 MPH

3.3 @ 6000 RPM = 173.02 MPH
3.538 @ 6000 RPM = 161.42 MPH
3.700 @ 6000 RPM = 154.35 MPH
3.917 @ 6000 RPM = 144.21 MPH


6200 RPM in 1st Gear:

3.3 @ 6200 RPM = 42.12 MPH
3.538 @ 6200 RPM = 39.30 MPH
3.700 @ 6200 RPM = 37.56 MPH
3.917 @ 6200 RPM = 35.48 MPH




The 3.7 gear set works with any rear end that will work with the 3.5 or 3.9 gear set...

So, basicly all you need is a 3.5 6MT pumpkin w/ VLSD or can be used with any Aftermarket LSD that works with the 3.5 gear set...

THe 3.70 gear set is: $480 for the gear set alone... You will also need the same pinion nut, pinion seal, spacer housing, bearing, etc etc just like with the 3.5 gear set...

to date ive done half a dozen of the 3.7 gear sets into auto's...

 

So with the Gear Set and All of the Fixin's to my door to have my shop convert my 3.3 5AT would cost in total? (Assuming I have ONLY the car and no other parts and will be buying everything from you at one shot)