What is the final gear ratio in the RB25 diff?

[74260zt]

I'm just about ready to hook up my set up, which is a RB26 to a RB25det trans, and I already have a 88 Shirro Edition VLSD with a 3:70 diff in my 260Z.

My main concern is will this 3:7 Diff be OK for the RB power band? I hear the RB's have a higher RPM range than the Zcar L6 motor...

Can anyone tell me what the OEM Diff ratio is for the RB25det GTS-T??

thanksjoelMY CURRENT MOTOR AUCTION

[PROJECTRB240SX]

4.36

[PROJECTRB240SX]

RB20 IS A 4.11240SX IS A 4.08300ZX IS A 4.11300ZXTT AND RB26 IS A 3.96

[74260zt]

Thanks! So...... it looks as if I'll be a bit on the bogging end of the RPM scale...

[mambastu]

R33 GTS-T manual is actually a 4.1 - I've checked this myself by counting the teeth

[Wykid 240]

SO what gear should you run with a RB25?

[mambastu]

SO what gear should you run with a RB25?

For general use I'd stick with the Skyline gearing. Its pretty good.

[74260zt]

Looks like I'll be stretching out each gear alittle longer with my 3:7 diff.

[IvoryJ30t]

RB20 IS A 4.11240SX IS A 4.08300ZX IS A 4.11300ZXTT AND RB26 IS A 3.96

actually, the rb26 uses a 4.11 rear [r32 does anyway]

and the Z32TT uses a 3.69

if you want to go taller, the Q45 uses a 3.58 diff.

[PROJECTRB240SX]

what color is the rb25det speedo sensor?what color is the rb20det speedo sensor?what color is the 300zx speedo sensor?what color is the rb26dett speedo sensor?

[PROJECTRB240SX]

YELLOW is the 16 tooth for the 3.36

BLACK is the 17 tooth for the 3.54

BLUE is the 18 tooth for the 3.70

WHITE is the 19 tooth for the 3.90

RED is the 20 tooth for the 4.11

PURPLE is the 21 tooth for the 4.38

[PROJECTRB240SX]

the rb25det I had, had a Purple Speedo sensor.The 300zxtt transmission my friend has, has a white sensor.

on the rb26dett you are right.... It should have read r34 6spd rb26 has a 3.96.

[PROJECTRB240SX]

Then you have to factor in wheel size to get the true final drive.

[mambastu]

the rb25det I had, had a Purple Speedo sensor.The 300zxtt transmission my friend has, has a white sensor.

on the rb26dett you are right.... It should have read r34 6spd rb26 has a 3.96.

Thats odd, my RB25DET has the red 20 tooth speedo sensor

Did you buy a half cut for your RB25 or a whole car ? I believe some of the GTS-T's came with some sort of electronic diff. I wonder if yours was one of those maybe ?

[PROJECTRB240SX]

IT WAS A MOTORSET.... SO YEAH ANYTHING COULD HAVE HAPPEND. I ONLY HAD THE MOTOR FOR A FEW DAYS.... BEFORE IT TRANSFERED HANDS.

[IvoryJ30t]

the R34 GTR is 3.545

[74260zt]

the R34 GTR is 3.545

yes, but I belive the R34 has different gear ratios in the trans though... that will affect the final RPMs, and thats what I'm trying to determine, if using a RB25det trans with a 3:7 diff, will be in the optimum rev range....

[Imissmyturbo]

I have found the 4:11 Diff to be a bit too short for the RB25 with Stock 240sx tires. I ran a 13.8 @ 104 and was almost at redline in 4th gear. I find when racing other cars on hyw that I have to back out before anyone else since 5th gear isn't a good racing gear. With a 3.9 or taller you will see a higher top speed in each gear. The gear ratio from 1-4th on the RB 25 transmission is pretty close so I think you can get away with running a taller final drive.

[BoostFab]

i'm thinking about using a J30 Diff for the RB20....iirc...it's 3.9~ish??? you guys know J30's top speed?

[IvoryJ30t]

yes, the r34 6 speed has shorter gears in the trans, made up for by the 3.545 rear.

the J30 uses a 3.916 rear.

if you give me a tire size, transmission, rear ratio, and redline, ill tell you the theoretical top speed.