Different differential for rb swap.

[MATTs14]

I've been looking into getting a different differential for my rb swap. Im running the stock s14 diff right now and it has lack lustre performance. I want something different that would allow me to maybe gain a few seconds on my track times. Maybe a closer ratio, taller gears, just anything different besides stock. Ive heard of people using j30 diffs and such but just wanted a little input. What are you guys using and what do you suggest?

[Carl H]

if you're looking for better response then the j30 diff is not the way to go...infact it will slow you down.best bet is a differential out of an r33 gts-t automatic (4.36 final) as it bolts right in with no mods...might have to swap axels but meh no biggie.

[MATTs14]

Ok thanks a lot. Do you happen to have any estimates of about how much each gear will do? For instance, my stock diff lets me do 70 in second for example.

[Carl H]

http://www.f-body.org/gears/stock final is 4.08, r32 manual and auto is 4.36, r33 manual is 4.10 auto is 4.36.use ka gear ratios as they are identical to the rb20's trans.remember that when changing the final drive you'll need to get a speedo corrector of sorts as it will change the speedo, higher final = higher speedo.

[SullivanRacing06]

im using a r200 out of a 90 gts n/a skyline vlsd, i enjoy top speed tho

[MATTs14]

whats the ratio on that? I thought i read on your build thread that it was a 2.90!!! Thats insane. What is your top speed just out of curiousity???

[SullivanRacing06]

to high, the fastest i went was 6900 in 5th at 21 psi, not going to say how fast that because there r the people who dont condone driving fast on the street, but my gps sure knows!

[MATTs14]

oh come on we all do it every now and then. Thats well over 200 if my calculations are right. I was playing with a gear calculator today and the largest final gear i did was a 3.55 since my friend has a new mustang. 2.90 would get you to 2 no sweat.

[meet07]

i have the j30 diff. i prefer taller gears over short. i also have a light weight flywheel so that will make up for the supposive.... sluggishness.

[MATTs14]

Does it feel better than stock? Im just looking for something that will help me out. Ive got a friend with an srt4 and he gets me from a roll almost everytime because he pulls way out of my efficiency range ie 60 which is too much to put in 2nd and too low for 3rd. I like the idea of shorter gears but i like the idea of top speed too. How much can you do in 2nd with the j30?

[Carl H]

low compression 2l i6 + tall gearing = suck.dont do it man...trust me.

[SullivanRacing06]

agreed w carl, mabey a 3.90 or 3.56 would be better for your app

[Carl H]

if you're shooting for 200mph you need to consider several things...for example

a) where the hell are you going to do this? aircraft landing strip is the only place i can think of...b)power output - car has to be capable of breaking past wind resisancec)aero, hate to break it to you but your stock bodied s14 is not gonna do it at around 130mph i noticed my s14 became SCARY light in the tail end.

with a big turbo on a 20 you'll need to keep the revs high if you want decent acceleration which means keeping your stock 4.08 or moving up to a 4.36 or a god forbid 4.63 final drive.

[wawazat8402]

c)aero, hate to break it to you but your stock bodied s14 is not gonna do it at around 130mph i noticed my s14 became SCARY light in the tail end

Agreed. I hit 145 in my FB one time and it was a handful and a half. It definitely helped me make the decision to pick a different car for my goals on the Texas Mile.

I found out that going faster is much less scary than trying to slow back down from going too fast.

[SullivanRacing06]

yea but a rb28 with a very large single turbo at 21psi sorta allows me to over come aero resistance, i have a stock bodied s13 with a sealed front carrage, a lip, and allota rack (rear is 1.5-2inches higher then the front of the car) helps push the back of the car down

[MATTs14]

lol i honestly have no desire to go 200 i was just wondering what sullivan had done. Ive done a little over 130 and it was plenty for me. I just wanted something that could help me keep my turbo spooled and like you said keep the revs up. I think i'll just stick with my stock rear end. I dont like the idea of having to shift every 2 seconds

[neonbomb]

Just remember everyone...

S-chassis = grocery getter

I know this is a bubble-burster for some of you. If you want a real Nissan car that will go high speeds safely, buy a 300zx.

[BoostFab]

to me, i like longer gear, it keeps me in boost longer and not shifting as sooner than shorter gears do. this is crucial for folks with higher power output. that's why the q45 3.5 is my choice, I won't be running out of gear before you and it results in higher top speed before running out of gear. just think about it, boosted car really doesn't matter, because you are under load and spin through 1st, 2end, 3rd fast anyways..shorter gear will not help either. who cares about off the line when you're launching at 4-5k rpm

this all applies to drag, but for x-cross, it's a different setup, you want shorter gears for quicker response.

Agreed. I hit 145 in my FB one time and it was a handful and a half. It definitely helped me make the decision to pick a different car for my goals on the Texas Mile.

I found out that going faster is much less scary than trying to slow back down from going too fast.

that's why the proper upgrade for your power range is supposed to go in hand with proper braking upgrade.
Modified by BoostFab at 6:32 PM 12/5/2008

[wawazat8402]

Braking wasnt the problem. I had plenty of brakes. The problem was keep the chassis stable while I slowed back down. I had Z32 brakes and HPS pads. I had zero fade on the brakes and the ATE fluid did great. The car just started feeling really light in the back end and made it a little unsettling while slowing back down.