R32 Gts-4 Rb25det Conversion

[GTS4onP]

Basically I have bought an series 2 RB25DET 4wd from a Stagea

Just wondering if leaving the front diff from the stagea with the rest of the driveline being standard gts4 would the attesa system still work fine with the different diff ratios (if there is any? presuming that their is, stagea was auto btw)

Also, if anyone who has done this conversion could you tell me what else will need changing? will be putting 25det loom and ecu in, manifold and external wastegate on, and a front mount intercooler on at the same time. So should be a good improvement over the standard rb20det

Thanks in advance

Cheers

[blind_elk]

It's a different ratio (4.083 v 4.375). Therefore the rears will be turning faster than the fronts, causing the ATTESSA to activate drive to the fronts, and the the front will want to accelerate away from the rear. Not a good idea.

I would recommend you get hold of a Stagea rear diff assembly and have the crown wheel and pinion swapped over into the GTS4's centre and housing. (The torque out of the RB25 doesn't justify the 4.375 ratios)

[GTS4WD]

You see, I read all these things. I know the diff ratios are diff from 32 and 33. Icontinue seeing these threads pile up with the same information.

But when I did my conversion. The ratio's were the same. I dropped in a DE which may have been the diffrence. Lower gear ratios for a less powerfull engine. Makes sence.

But yes, the easiest way to do it is as Elk said. swap the wheel and pinion over.

Or get a 4.375 rear diff. The 32 gearing is ver short as it is, depending on what your planning to do with the car you may find it a better option to change to a larger diff ratio.

Edited October 28, 2008 by GTS4WD

[blind_elk]

You see, I read all these things. I know the diff ratios are diff from 32 and 33. Icontinue seeing these threads pile up with the same information.

But when I did my conversion. The ratio's were the same. I dropped in a DE which may have been the diffrence. Lower gear ratios for a less powerfull engine. Makes sence.

But yes, the easiest way to do it is as Elk said. swap the wheel and pinion over.

Or get a 4.375 rear diff. The 32 gearing is ver short as it is, depending on what your planning to do with the car you may find it a better option to change to a larger diff ratio.

No, the R32 already has 4.375 rear diff ratio (and a 4.375 front diff ratio). The Stagea has 4.083 (@ both ends!)

There are 2 options:

1. Swap the front diff from the RB20 into the RB25, so you retain the factory R32 4.375 ratio.

2. Swap the C/W and Pinion from a Stagea REAR diff onto the diff centre of the R32 REAR diff (the Stagea seems to run an "open" rear diff, not a Viscous Coupled rear diff like the R32). This way, you get the Stagea 4.083 ratios.

With the torque of the RB25DET, I would go for option 2 while you have the opportunity and everything is out of the car. (Because I've been there, done that)

With option 2, you will need to change the speedo drive gear in the gearbox to a R32 GT-R unit, to keep the speedo readings correct.

[GTS4onP]

Ok sweet thanks, does anything else run the 4.083 rear diff ratio that will still fit upto 4wd driveline?

and if i went with option 1 (rb20 front diff) what sort of rpm would the car be sitting at at 100kph in 5th gear (currently about 2900rpm, pretty high for a 2ltre i think)

will eventually want to put a gtr driveline in it at some stage, not at this point in time though, want to get it back on the asap now.

also, my right front CV joint is f**ked, what CV joints do they take?

thanks for your help, good to see a few GTS4 owners on here aswell

[blind_elk]

Ok sweet thanks, does anything else run the 4.083 rear diff ratio that will still fit upto 4wd driveline?

Not that I'm aware of.

and if i went with option 1 (rb20 front diff) what sort of rpm would the car be sitting at at 100kph in 5th gear (currently about 2900rpm, pretty high for a 2ltre i think)

Should be exactly the same because you'd still have the factory driveline.

[GTS4onP]

Ohh and also, to swap the diffs over, do you need to swap the whole sump or can u take just the diff off buy itself?

[heller44]

4.375:1's in mine, sits about 3100rpm at 110... nothing major. Nice and sprightly off the line.

Edited October 30, 2008 by heller44

[bozodos]

in mine with stagea RB25 and box and GTS-4 diffs it revs at around 2880rpm at 100km/h and 3060rpm at 110km/h dosen't feel like the engine is revving its tits off (its a pig on fuel anyway so fuel consumption remains at around 18l/100)

Edited October 30, 2008 by bozodos

[blind_elk]

Ohh and also, to swap the diffs over, do you need to swap the whole sump or can u take just the diff off buy itself?

You can swap just the diff itself. You MUST swap both the Crown Wheel and the Pinion - they are a matched set. Have fun undoing the pinion retaining nut!

[RipNGrip]

Hey guys, i have a r32 gts4 with a stagea rb25 conversion. I had a work shop do the conversion and they had a few issues, one of which was the trying to attach the rb 20 front diff/sump to the block (rb25) eventually they ended up machine the bottom of the block to fix the front diff axial across the bottom of the sump. I am pretty sure, thats what they did. and now if i am full lock or accelerate quickly i get 50/50 touque split which i assume is from the rb20 rear diff and the rb25 front diff! umm thats a bad thing........oh shit~

[GTS4onP]

You can swap just the diff itself. You MUST swap both the Crown Wheel and the Pinion - they are a matched set. Have fun undoing the pinion retaining nut!

ok sweet, so how is the diff attached to the sump? i thought they were one piece, so ur saying the rb20det front diff will just bolt upto the rb25det sump?

[blind_elk]

Remove the cover plate off the diff housing, remove the drive shafts, and the diff centre basically falls out. To undo the pinion nut, lock out the flange against the block with something like a cold chisel, then use a BIIIGGGG breaker bar to get the leverage to undo the nut. The pinion comes out the same direction as the centre.

[GTS4onP]

Ok sweet as, cheers for your help mate, any other little things that will need to be done when doing this conversion?

[RipNGrip]

FYI, it doens't just bolt on there is a miss alignment of the front drive shaft

[GTS4onP]

oh ok, whats the solution to that?

Cheers

[blind_elk]

FYI, it doens't just bolt on there is a miss alignment of the front drive shaft

Sorry, but that's rubbish. When I did the swap in mine, it all just swapped over.

[zertek]

Use GTS4 rb20det sump & diff and bolt that on your stagea rb25det motor. It bolts straight up. Done it before. RB20det 4wd ratio's are shorter and more fun. Hence alot of GTR's convert to GTS4 ratio's

Also listen to blind elk. he knows what he's talking about and helped me ALOT via PM's last year, while doing this very same conversion

[GTS4onP]

Use GTS4 rb20det sump & diff and bolt that on your stagea rb25det motor. It bolts straight up. Done it before. RB20det 4wd ratio's are shorter and more fun. Hence alot of GTR's convert to GTS4 ratio's

ok sweet, bolting the rb20det sump and diff on sounds a whole lot easier if it just straight bolts up. any probems with running rb20det sumper coz maybe be smaller or anything silly like that. lol soz bout all the n00b questions but im learning

Cheers guys

[RipNGrip]

i have heard both.... that it is a same bolt on but i can tell u, some of them dont! i had it done at opition one auto and they showed me the difference between the two sumps! hey i had to have the block machined