speeddemon7

Alright so I have a question for everyone.Ive seen that some guys with a 5 speed fd actually consider using 3.9 rear gears because it will make the lower gears much more usable with higher horsepower applications.
My fd is currently an automatic but I want to convert it to a stick in the near future.
The car has the following mods.Blitz intakes,downpipe,effini y pipe,blitz catback,greddy profec b spec 2.Hopefully soon I will also have a pfs smic.
I want to run a midpipe with either the sequential twins or parralell twins.I also want to run a apex power fc.With all of these mods will it be beneficial to keep the auto rear end? or would the 5 speed rear end be a better choice?
I have a buddy that has a 5 speed fd and he has the same mods I have plus the others I have mentioned that I want.Hes running the twins in parralell.Now he says in 1st and second gear he has traction issues.Would he and I benefit from the 3.9 gears perhaps? Just trying to see if I really need the 5 speed rear end or not.Hopefully someone can help me out on this.

ejmack1

gett he 4.1's

the car is very sluggish otherwise....

Wargasm

Personally, I'd stay with the 3.9 until you get your car converted to 5 speed and you get your engine set up the way you want it. Then if you feel the car needs more 1st gear "oomph", go for it.

I have the 4.1 in my car and in first gear I have to go half throttle or I get terrible wheelspin. However, once I'm on a roll, I have no problem with the 4.1 at all. You can always do the 4.1 (or 4.3, 4.7, or 5.12) gears later... I'd wait until your engine is all set up to make the decision.

I wish someone made a new gear set for our cars... I'd make first a decent amount taller, second I would just tweak a bit, and third and fourth are OK how they are I think.

BATMAN

5.12??!?!?!??!?

and i thought that 4.7 was already crazy.

speeddemon7

yeah.5.12 is a bit of an extreme.
So then the 4.1's with the given mods should be the optimal setup correct?
my buddy says with the mods he has at 16 psi the car puts down 340 rear wheel horsepower according to Steve Kan

ManGaZeRo

iTrader: (1)

Since your switching from 3.9 wouldn't it just be better go little higher to 4.3 like the 99 + 7s.

BATMAN

agreed...... no point in a small jump to 4.1.

Mine as well look at 4.3 or 4.7

speeddemon7

how much differentce is there between the 3.9's to the 4.3's ?
The reason I asked was to know whether to get the companion plate which allows the use of the automatic rear end rather than switching to a 5 speed rear end.I supposed I might as well do it right the first time.Now suppose I pick up the 5 speed rear end.Would it be worth the 475 plus labor to get the ring and pinon changed to the 4.3's?

Black97VR4

If you do this all at once your car will feel MUCH faster accelerating going from an auto with 3.90s to a 4.33 set.

speeddemon7

thanx for the input once again guys.Ill be on here again asking some questions once the project is underway.

BATMAN

if u go from a 3.9 to a 4.1 = wow

" " 4.3 = WOW
" " 4.7 WOW!!!!! WTF!??!?!?!

turbojeff

iTrader: (30)

If you get wheelspin in first gear without dumping the clutch then you probably need new/better tires.

I drove a 363rwhp FD with 4.88 in it. No wheelspin on dry pavement.

Get the 4.10s.

jimlab

Where did someone get a set of 4.88 gears? That's one I've never heard of before.

3.90 - 39 tooth ring gear, 10 tooth pinion gear
4.10 - 41 tooth ring gear, 10 tooth pinion gear
4.33 - 39 tooth ring gear, 9 tooth pinion gear
4.70 - 47 tooth ring gear, 10 tooth pinion gear
4.88 - 39/8?

turbojeff

iTrader: (30)

I dunno, that is what he told me he had, he got them from Japan. I can tell you for a fact they were lower than 4.33s.

PM Spank and ask him where he got them.

turbogarrett

iTrader: (1)

sell the 3.90 gears to me, or we could work out a trade? i am assuming that all we would need to do is trade ring and pinions? 4.10's are a little steep for my setup.

ManGaZeRo

iTrader: (1)

How much are you willing to pay for the 3.9

Outkast

I have an auto 3.9 with 300 hp and a stick 410 with 400+hp. What if I were to switch their rear ends? I am seriously considering it. Is it hard?