RB25 Gearing......

[Imissmyturbo]

After driving the car for about 3 months and doing some highway pull against my friends in various cars I have figured out the gearing on the RB25 sucks. Basically it's 4th gear that sucks. It tops out way too soon. In fact in the 1/4 mile I am currently running a 13.8 @ 104 and I am just shy of redline by the end of the track. I guess my two easy options are a different rear end for gearing and larger tires. I have an R32 3:11 rearend in the car now. I guess throwing the stock S13 diff in and welding it would help just a little bit. What other rear ends could I consider? How about changing gears from other rear ends? You guys who are running in mid 12's what gear are you in at the end of the 1/4?

[gprodigy85]

i did some "theoretical" gearing speeds by dialing in the rb25det redline, gear ratios for 1,2,3,4,5th gears, and the final drive from a j30 and heres what it told me it should be, again its theoretical

1st: 41 mph2nd: 70 mph3rd: 103 mph4th: 135 mph5th: 179 mph

[Imissmyturbo]

What is the ratio on the J30 rear? What tire size are you going with? The standerd R33 manuel says, 1- 55km 33 mph2- 100km 60 mph3- 145km 87 mph4- 180km 108 mph*

* I think that the speed limiter is why it only goes that fast in 4th.

[gprodigy85]

the j30 is a 3.96, and i was putting in my 245/45/17 which is like 21.3 inches tall

so technically with your 3.11 you should be way higher than that... but what tire size are you running out back

[PROJECTRB240SX]

IT SHOULD BE A R32 4.11

[gprodigy85]

well 4.11 would explain it... a j30 or z32 would help you a lot i think...

[74260zt]

IT SHOULD BE A R32 4.11

That would be a very popular diff it those were indeed the gears (3:11). I know a ton of turbo z car guys who'd give their left nut for those gears...

[PROJECTRB240SX]

WHATS SO GOOD ABOUT SUCH A LOW FINAL DRIVE? YOU REALLY CAN'T USE IT ONE THE STREET OR DRAG STRIP.... YOU'D BE ABLE TO UTILIZE THE FULL POTENTIAL OF SUCH A LOW GEAR RATIO IN LIKE A BONNEVILLE SITUATION.

[74260zt]

Load = Boost

[Imissmyturbo]

LOL..Ya 3:11 would be pretty dam tall. It's 4:11. So a J30 rear end is taller. hmmmm. Wonder if anyone would want to trade for my rear? I know that would help me out a lot cause 5th gear in my car sucks for acceloration.

[PROJECTRB240SX]

JUST GET A 300ZX TT REAR END.

[gprodigy85]

the problem is with a 300zx you have to get output shafts, a j30 its a bolt up job for 95+ 240s if you get a 95+ j30 rear end... and it can be gotten for under 200$ at tons of junkyards.

[PROJECTRB240SX]

WHY CAN'T YOU JUST SWAP THE REAR END COMPLETE? LIKE THE R33 REAR END AND AXLES.... JUST SWAP THE DIFF COVER AND SLAP IT INTO THE REAR SUBFRAME OF THE S13 OR S14.