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RB25DET conversion in R32

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I'm thinking about doing a RB25DET conversion on my GTS-t. I'm sick of the turbo lag, especially as it's my daily. I was thinking about RB30DET but I think that'd cost too much to do it properly.

Should I buy a halfcut or would that be a waste of money?

I figured things I'll need in the conversion are:


- RB25 gearbox

- clutch, flywheel (necessary? are the RB20 ones compatible?)

- ECU (I'm thinking Power FC or Microtech if I can afford it)

- bigger / better brakes (eventually)

This makes the halfcut option sound good but would people be after the extra parts like front guards, headlights, front bar etc...?

I've sourced one for around $4600 - is this good?

If there's anything I've missed please let me know.

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i would just go and get engine, gearbox, computer and loom. wouldn't bother with the front cut as you would HOPE to sell everything out of it.

a RB30DET isn't such a bad idea if your going to spend $4600 on a front cut..

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... I'm sick of the turbo lag, especially as it's my daily. ...

LOL...scratch up another owner turning his back on the RB20:)

RB25 would be great, a lot more responsive and decent power, but at the dollar figures to do the conversion...well i think an RB20 with an equiv amount of money spent on it is going to be more powerful, quicker and and more robust.

That said if you want a better building block for more mods down the track, or you flat out hate the response of the RB20 then i suppose you dont have much of a choice:(

Go for a ride in a 230rwkw RB20, they are still fun and they spin nicely up top with a bigger turbo..im pretty sure they are considerably quicker then a 200rwkws std RB25?!?!?!?!?!?!

I hate to day it, but unless you are willing to commit money to the R32, its perhaps best to just start with an R33:(

...and a front cut aint that bad an idea as you get the brakes and rotors as well, plus so many bits and pieces that make the converiosn easier, and wth good timing you can normally flog off front guards, control arms, tie rods, stub axles etc to drifters on a steep learning curve:)

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Been there, done that.

But now I can pull stumps out of the ground. The RB25 has SOOO MUUCCHH torque down low, from the VVT. Add a Wolf 3D 4+ (or other aftermarket ECU), and you are starting to talk numbers. Mine, running 10psi on 95 octane crap now punches 180 awkW (RB20 had 115) - equivalent to maybe 210 rwkW, 240+ fwkW, and that's approaching HSV Commonwhore, but doing it with 2 less cylinders, 3 less litres, but 1 more camshaft.

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Im with Roy. Before spending say $5-7k+ to do a conversion maybe look at a better set up on what you have. Im guessing if you have a problem with lag you got a bigger turbo, so maybe manifold design, after market computer, some head work, cams etc. And you would have spent a fair bit less money.

And end of the day, rb20 goes boom, its not as much to get a new motor as if a rb25 goes boom :D

Just my thoughts anyway.

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I'm in the same boat. In a month i'll have rb25 power too. It's already in the garage getting timing belt and water pump changed and cam gear installed.

My rb20 is well rooted and badly in need of replacement, compression well down, problem with random misfiring that i could not find after swapping every bloody thing attached to the engine.

So for about 1k extra for a replacement engine loom and ecu and a lot of work in the back yard i'll have an extra half a litre to play with. And the 25 will actually match my GCG stage 2 highflow unlike the 20, particularly with the manifold thats going on it :)

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Forgot to mention you need to mod the tailshaft if you use rb25 box and yes an rb20 clutch will fit.

You will find the engines coming out of front cuts seem to have a better chance of being healthy. I actually did a deal and pulled the engine out of the cut in the wreckers yard along with loom and ecu, didn't want the box (it was rooted anyway)

4k+ seems to be the going rate for a rb25det manual frontcut from wreckers. You will probably be able to find one cheaper if you keep looking around and go to some of the less known import wreckers.

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err...I have a stock turbo :) I find it's too laggy for daily driving, there's not a lot of response down low which sucks. I'm running 12psi as well (no boost controller, just a full exhaust + front mount).

BHDave - got any suggestions on wreckers? SSS and JustJap got expensive :)

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$4k... Wasn't there talk on these forums where people were able to make a rb30/25 for under $4K installed in the car?

wouldn't that be a better option?

anyway, a mate used to have a R32 which he installed a RB25 in to.

with bosh fuel pump, GTR intercooler and 10 psi and stock ECU... he was making close to 180rwkw.

He was still using the R32 GTST gearbox with short shifter and lets just say that he didn't baby the thing..

the stock gearbox will hold out fine for a mildly modified rb25..

I mean there are others on here with over 200rwkw in their R32's with rb20 and using stock gearbox so I'd say just get the engine and ecu and loom for now and get the gearbox once you break the stock one..

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err...I have a stock turbo :) I find it's too laggy for daily driving...

LOL...thank god im the opposite, daily driving i like the fact that the power doesnt hit low and hard like skyline_geoffs R33. Once a month i get the sh1ts with the p1ss poor response, but day to day im never in a hurry so its cool.:)

Thats said if you have the funds, then there is little doubt the RB25 is a better building block...just do the numbers before you start and be sure you know what its going to cost and after those dollars have been spent you know the performance to expect:)

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err...I have a stock turbo :P I find it's too laggy for daily driving, there's not a lot of response down low which sucks. I'm running 12psi as well (no boost controller, just a full exhaust + front mount).

BHDave - got any suggestions on wreckers? SSS and JustJap got expensive :(

Damn, you really want it all don't you :) Ever considered a V8?

I wish i had stock response.

You could try Jap Import Spares at Lansvale 9755 7533 which is where i got mine, Maybe Ichiban at moorebank if they are still around, they've been doing engines for years, Jap performance while your in moorebank, Auto disposals (can't remember where they are though). Aria Jap at Yennora reckon they are cheap too, can't say for sure, 9681 6444.

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Lag on the stock turbo? Far out dude, maybe it isnt stock! Mines full 12psi at 3000rpm 1/4 gas in 5th no worries. Its just off the line if I dont give it the revs I have a prob, then its more no revs than the turbo.

Im with BHDave on this now! Get a bloody V8 ya hoon!

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1998cc...meh, whatever happened to the good old days where you strapped big turbos on 4/6 cylinders and just relied on boost and revs to make good power up top with light switch power delivery....bring back the Sierra Cosworth, the real mans turbo car.:P

None of this wimpy repsonse rubbish, just massive lag and big hits of boost with 100% increase in engine power over 1,000rpm :whackit:..................:(:):):)

Says the laggy RB20 owner:(

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Lag can't be that annoying with stock turbo... If your just cruising, daily driving you don't need to go that fast anyway and if all of a sudden you want to go fast JUST USE THE GEARS that is what they are there for, heel toe or just change down until you get 3,000rpms and off you go... whats the point of having a 7,000rpm redline if your going to ignore 60% of the power band...?

As Roy said revs + boost = speed and acceleration... now a T88 on a CA18DET that is LAAAAG!

All that said I have RB25 and love it... so go for the conversion if you can afford it! Bigger engines in smaller cars are always a good idea;)

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I could have done a reasonable RB20 re-build, probably with the 4AGZE pistons for a bit of compression. But I heeded the advice of people in the know who advised me that "cubic inches DO count". So I went the RB25 route.

I don't need to worry about lag, because the engine already has a HEAP of low-down torque to get me into trouble.

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i got a NEO rb25det 4 sale if your ever interested :)

yes I know. I want :( Very sweet engine...

BHDave - I was also thinking of dropping a Nissan VH41DE in (4.1L V8 :() as it's cheaper than a RB25DET but I like boost and I've already got my car set up for a new engine (all the extra mods have pretty much been done).

The RB20 is fairly laggy - not enough torque, which is why the SR20 would've been better standard BUT the engine note sucks. I think more cubes in the R32 would be better as it's heavier than say a Silvia / 180 but got less power :) So a RB25DET is like the perfect solution.

GTST - $4K? sounds like a few things were skipped. The guy must've had the right tools or known the right people to do that for that price.

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ROFL...at your sig

 RB20's can go to hell...(sorry Roy)

...and above my avatar:)

 RB20s have feelings too

All i can say is make sure you budget enough time and money to do the swap, and appreciate that you are still only going to ennd up with 180-200rwkws, and end up with an engine that is very strong and good for some serious power, but is more susceptible to piston damage then the RB20.

No doubt the RB25 is a better option, throw in time off the road, cost, insurance just be sure the scales are still tipped in favour of the swap.

My car is laggy as hell, drives ppl insane when they drive it with no real urge under 4,000rpm, but its fun when it hits boost and pulls...thats the reason i love turbos. If i had a 3L no doubt i would have 650hp turbo on it so that it would still have the same amount of lag, its just that i would have an extra 1.0L for putting around off boost.

Do the RB25 swap, if you want turbo defying response, then with a HKS 2530, well in an R33 i still say its the best road car i have ever driven...:)

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hmm, thinking of doing this conversion myself, as i have access to a very cheap R34 Neo Front Cut (i'll be selling the headlights + front bits for R34 headlight conversions later...)

Just to clear a few questions up, i've searched around a bit, but need a definate answer on this.

it's an R32 gtst 4 door manual rb20det

I'm going to put in the NEO RB25DET Manual (but keep the RB20 gearbox)

Would you have to use the NEO computer (because it has VVT) and wire up all the ancillaries to the NEO's loom? or can you use the RB20s computer & loom.

Or would it be better to go aftermarket engine management?

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Use the r34 loom and ecu(or an r34 pfc), there are a few bit's and pieces that the r32 ecu wont run, like the vvt which in the r34 is constantly variable, unlike that r33 which is on or off so easily controlled with a simple switching module. You would also be swapping plugs on the injectors and lengthening bit's of the loom to suit the different positions of the air regulator.

You'd also need to get the ecu chipped/tuned to suit the rb25 where as the r34 will run it no problem.

On the other hand there will be a fair amount of work required to get the r34 loom plugged into the r32, particularly the under dash plug

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