Best Option, RB24??, 25 0r 26

[PRO_32]

wouldnt a Rb20 stroked RB24 be cutting it a bit thin (significantly weaker Block)

I mean from a long term reliability point of view

[DoughBoy]

It also changes the cars character too much!

Go for a drive in an R32 2L turbo, then an R33 2.5L turbo, then consider that the 3L is going to have at least then same difference in torque over the 2.5L. I hate to say it, but after driving an R32 with a few mods it felt gutless compared to the superior driving experience offered by my R33. Hoses popping off not included

[Cubes]

Exactly Doughboy,

What made me go the RB30 route was driving mine then jumping straight in to a R33 with a few mods that made 175rwkw. Mine at the time was making 164rwkw but felt quicker 'once' it got on boost.

The R33 had so much more torque and spooled the turbo so so much quicker. There was none of this waiting around until 3300-3500rpm to get the kick in the back, put your foot down and power was there. The RB20t has really left a bad taste in my mouth. Maybe because I came from a mild VS 5ltr 5speed, even that was still gutless below 3000-3500rpm.

The RB30DET so far has cost me.

VL Series II RB30 Short motor - $150

Rebuild, Balance, Wiesco 87mm RB25 Pistons & RB30 headgasket - $3500

R32 RB25DE Head - $750

R32 RB25DE Head work & rebuilt (didn't need to be done, I did it anyway) - $1100

By using the R32 RB25DE head you are able to use all of your existing RB20t bits apart from the RB25DE plenum that looks the same as the RB20t plenum but has larger ports. Ue the RB20t fuel rail/injectors, RB20t CAS, RB20t coils/ecu etc.

Really depends what you want. I'm going to be making hopefully around 390-400kw at the flywheel with around 650-700NM of torque around 3000-3500rpm.

You don't have to buy a new turbo with the RB30E all it means is that the turbo will spool up a good 1000-1500rpm earlier (at least). At the same boost you may even make more power over the rb20t as the RB25DE valves/ports are larger hence less restriction so you will be getting the same airflow in to the pots at a lower boost. Hence same power at a lower boost.

I've weighed up the pro's and cons. If you have an R32 it works out pretty close if you were to build up a RB25 block. i.e Purchase the block 800-1000 which is actually the similiar price for a RB25DE head so yer it works out pretty much the same.

I like torque not rev's, I really have come to disslike the character boy racer feel of the RB20t when trying to take off from the lights quickly to get in front of another lead footed older man in his auto v6 commodore. Basically I hit boost in first gear and the rears start chipring. The RB20t is to on/off for me.

[PRO_32]

Joel you put up a good arguement in favour of ditching the 2L in place of a 3L , But i'd like to hear ppl's opinion's of hassled faced at the engineering/registration stage (is a 3L in a 32 legal)??

Also the parts you said you have bought was that all thats needed to do this conversion or are there other misc expenses like new exhaust manifold and so on????

[Cubes]

Exhaust manifolds will bolt up to the RB25DE head no problems. It has the same bolt up pattern as the RB20/25DET.

With regards to registration, the largest legal engine that can be placed in to the GTS-T on the weight equation is a 2.6ltr turbo.

BUT I'll put it like this.....

When you buy a 'new' RB30E block from nissan it has no engine number on it.

The RB30E above the engine number is scribed in with an engraver. Pop down to your local holden wreckers and ask to look at a RB30E short motor's engine number. You will be left wondering if some one did a dodgy scribe on the block, that is the way it comes from factory.

Providing you get the series II VL block then everything lines up.

Check out the RB30DET guide in my sig. Its not totally up to date but it does give you a good idea.

Another option is to grab yourself a RB25DE from a R32, build that up with a set of forged pistons, slap on your old engine number and no one would be the wiser.

One more thing.. The RB30E block is slightly taller.

It can't be noticed though providing you do a good job on the cam belt cover.

If you are worried about the block height then build up a R32 RB25DE engine. You can then still use the RB20T ecu, injectors, coils etc.

I was going to go the R32 RB25DE route however the curiosity of extra torque got the better of me.

I keep thinking how much torque my old NA 3ltr 5 speed had with a 3.45:1 diff ratio, it had very similiar off idle torque to my old VS 5ltr 5 speed, well until 3000rpm in the v8 then it was gone.

I then think of how the R32 GTS-T diff ratio has a 4.363:1 & a twin cam head and start grinning.

If you have ever experienced the difference from a 3.08:1 diff ratio in a V8 manual to a 3.55:1 you will know exactly why I'm grinning.

So yer.. Best bang for buck without having to stuff around to much with ecu's wiring or even registration would be to build up a RB25DE short motor then bolt everything back up. No one would be able to tell the difference unless they opened it up.

Jumped around a bit in this post from adding bits..

[PRO_32]

Tell me if im reading you right-

can use RB25de (R32) short motor and replace my bottom end with it ( assumeing i will use the 25de crank/Rods ) Bore can stay as is and bolt everything back up from original motor..

cheers for the info Joel

[Cubes]

You will have to use the complete R32 RB25DE NA motor. Bottom end, Head & Plenum. Compression may be a bit high with std pistons as it is after all a NA motor.

You can use your RB20t sensors, injectors, coils, oil pump etc.

You can't use the RB20t head as the bore is smaller + you would be silly to as the RB20t inlet valves are around 29 or 30mm can't remember exactly, the RB25 inlet's are 34mm. Ports on the RB25 are are around 5-6mm bigger.

I've seen RB25DE motors go for around $900 complete.

The RB25DE has a slightly weaker exhaust cam to the rb20t.

Rb25DE 232dur 7.3mm lift

RB20t 240dur 7.8mm lift

[Elithrar]

It may not be the most ordinary way of going about it, but I'd go a RB20 stroked to 2.2L. Their naturally revvy nature (over an RB25) means that the engine would cope well with a stroke, and the added torque that stroking produces (much like when Mitsubishi upped the 4G63 from 1.8 to 2.0 litres) will be great.

Plus, you know that you are starting with a good motor, as it is yours, and you'll have forged pistons and rods, so durability won't be an issue. Coupled with an R34 GT-t turbo (@ ~1 bar), it would be relatively unique, quick, and still be legal. It's something that I would like to do to my R32 GTS-t after I get some solid mods into it.

[Roy]

I hate to say it, but after driving an R32 with a few mods it felt gutless compared to the superior driving experience offered by my R33. Hoses popping off not included

Hey I hope your talking about someone elses R32 :Oops: Its twice as bad now but at least she has some top end.

how do the rb30 internals handle that much revs?

Why wouldnt it handle those revs, noone questions how M3s rev. The M3 3.2L has a 91mm stroke vs the RB30s 86mm, so dynamically it should be a better revving engine. So comes back to metallurgy, and the RB30s crank is fine, and for 7,500rm and the sort of power we are talking about here, even the std rods should be fine. The cams/valvetrain may not be all that well suited to making power at these revs, so maybe different/bigger cams but i dont think reliability should be a concern.

There seems to be the attitude that if its bigger it wont rev... can be true but not always.... is my reasoning sound?

Getting back to the weezy RB20 thats getting sand kicked in its face, if i read right, Drifto is looking at using the same turbo and gearbox. Is wanting response and a bump in bottom end torque...and has a cooked engine on his hands. I think an RB30/25 is overkill.

An RB20 that has been bored out to 82mm (81 if you are really that paranoid, some Japs even use 83 pistons) with some nice forged pistons with about 8.8:1 compression, balanced crank/rods would make for a great improvement.

If you happen to stumble accross GTR crank/rods then great there is an extra 200cc. Either was as part of doing the 82mm pistons, you will need to modify the combustion chamber to suit the new bore diam, so as part of the process a quick tidy up of the ports is a cinch.

Bolt it all back together and you will have an engine that is a known quantity, lighter/stronger forged pistons (lower intertia), extra compression, with a slighlty better flowing head.

It can all be used with his current turbo, gearbox, clutch etc and will be a different animal off boost courtesy of lightened internals, higher compression, and bigger displacement. And can even run 1.3 or whatever boost the turbo can safely handle so as well as having more bottom end is likely to get another 20-30rwkws top end.

[Bl4cK32]

 

Getting back to the weezy RB20 thats getting sand kicked in its face, if i read right, Drifto is looking at using the same turbo and gearbox. Is wanting response and a bump in bottom end torque...and has a cooked engine on his hands. I think an RB30/25 is overkill.

All signs point to larger displacement. How so is this overkill? U can use the std gearbox and turbo. Who says the rb25/30 has to be a performance engine? A std rebuild would cost approx 770 of the bottom end (new std pistons, bearings etc) and a head (750 without rebuilding it) and there's an engine that could take 250rwkw with safe tuning. (some will/wont agree:))

Isnt RIPS running 10's with the same type of engine? (yeah i know nos + gts4)

He said he wants power down low - great example for rb30det

Other support systems require upgrading whether he has the rb22 or rb30 anyway.

[Roy]

All signs point to larger displacement. How so is this overkill? U can use the std gearbox and turbo. Who says the rb25/30 has to be a performance engine? A std rebuild would cost approx 770 of the bottom end (new std pistons, bearings etc) and a head (750 without rebuilding it) and there's an engine that could take 250rwkw with safe tuning. (some will/wont agree:))

 

Isnt RIPS running 10's with the same type of engine? (yeah i know nos + gts4)

 

He said he wants power down low - great example for rb30det

 

Other support systems require upgrading whether he has the rb22 or rb30 anyway.

I suppose ppl will alwasy have different feelings towards modifying a car. Its a synergy thing, trying to get all parts to work together, and in this case use as many existing parts as possible.

But he already has a motor to use, so that saves the purchase of an RB30 bottom end ($400), the RB25DE head ($800). There is some forged pistons, or at least a set of 4AGZE pistons. If i was using an engine for club level motorpsort then id at least want forged pistons. (If you were to rebuild using std cast pistons what compression ratio do you end up with on the RB30DET?)

And as for power down low, yeh its great, but with too small a turbo you could soon find back pressure out of control and power trailing off at 4,500rpm. Interesting to hear from someone that has used the std turbo on a RB30DET. If it works, then my concrens about Drifto's turbo being too small would be eased.

The legalities of it isnt an issue for some, it is for me...

[Bl4cK32]

I guess your right there Roy - on some points

A rb30 short motor can be found for $100 (i bought mine with a cracked head) and the block etc are all fine.

Im not sure what compression ratio u get on the 30det with the cast pistons, but it has been discussed in the sticky thread at the top. Im not sure of the exact details but in mine being built the pistons are rb25 forged items and the cr is 8.5:1

As for the std turbs....ask -Joel- he will know more about it. I know with the rb25de head & std cams (i think) power starts dropping off over 5500rpm. (good excuse to upgrade) but it gives great fuel econony.

I guess it comes down to how much u want to spend, cos once u go down a certain path the spending snowballs.

[PRO_32]

of then so...

Rb25 Crankshaft

Rb26 Connecting Rods

82mm Forged Pistons

Bore CC to suit new Piston Diamiter

Modify head Ports

Now...

HKS 2835pro

external manifold

Tuned length manifold

PLus

All the usual peripherals.

PFC

550cc inj

Pump (910 or 044)

reg (if needed)

And

A bit of longjevity for the engine

aluminium Rad

Oil cooler

Have i left anything out here???

Assuming this kinda setup allows safetly running 20-25 Psi and turbine and compressor sizes matched to this application, With your experiance what kinda power could this hybrid RB20 pump out...??

The rational behind my thinking is that whilst it can be done with RB25-30

or with rb25de thats all well and good. But IF it can also be done with the original rb20 well that if more my style.. Id prefer to make more power with less capacity..

Any thoughts or suggestions??

[Roy]

Any thoughts or suggestions??

All us RB20 owners are probably gooing "oooohhh....ahhhhhh!!!" over such a setup.

Considering there are 10 second GTSTs running the RB24 setup in Japan, albeit with T88s, i dont think that you can question there ability to punch out good numbers, its perhaps the expense required. So if the 2835 can throw out enough cfm on an RB25 to make 280rwkws, i cant see why similar number (maybe higher as you could wind the wick up to 1.5-1.7bar) wouldnt be achievable from an RB24.

You list RB25 crank. Since you list RB26 rods, then its probably easier to pick up an RB26 cranks and rods, that way you get the extra 2mm stroke. Since your boring/decking etc the block anyway you may as well just machine it to clear the bigger swing of the GTR crank.

I have a build up in mind similar to what you have listed, the main things i would want to do as well would be some cams/valvesprings with some head/manifold match porting, and an RB26 water/oil pump.

[Elithrar]

Using the GTR crank and rods is something I didn't think of; it'd be quite a cost-effective option. Coupling that with some forged pistons (either stock bore, or overbored) and you'd have a relatively strong engine for not an incredible outlay (or at least I would think). What would be the price for something like this?

[PRO_32]

Roy my only worry with using the 26 Crank and rods is that you might end up having to take too much out of the block.. Thoughts on this???

ohh and i tottaly forgot about the head mathc porting and cams would really be par for the course if your doing everything else stated, You say valvesprings in your experiance have you found them to be a weak link???

cheers

[Sydneykid]

Hi elithar, I think I need to repeat something I posted earlier.....

"An RB20 has a 69.7 mm stroke and RB25 is 71 mm, RB26 is 73.7 mm and RB30 is 85 mm".

Increasing the stroke by 1.3 mm from 69.7 mm (as in RB20) to 71 mm (as in RB25) is not going to make diddly squat difference to the engine's ability to rev. Even the 4.7mm increase is going to have no effect, if you use an RB26 crank.

It isn't until you get a 15.7 mm difference (RB20 to RB30) that increasing the stroke has any effect whatsoever on the engine's ability to rev. And that isn't the issue anyway. The fact is when you have a 3 litre turbo engine it doesn't have to rev to make truck loads of horsepower. I have no idea why anyone would want to make 700 bhp at 9,000 rpm in a short stroke engine, when you can easily make 700 bhp at 7,000 rpm in a long stroke engine. It is still 700 bhp for heaven's sake!

Just to kill off the RB31DET's don't rev crap, we are at 8,500 rpm and still climbing with a standard crank and block. Problem is (remembering that horsepower = torque X rpm / 5250) the horsepower outputs are getting scary high! Maybe 7,500 rpm is all you would need, considering the exponential rate of increase in rebuild frequency as rpm rises ie; we rebuild a 8,500 rpm engine almost twice as often as a 7,000 rpm engine.

Hope that adds to this interesting thread

[Sydneykid]

Hi pro 32, the stroke increase (RB20 to RB26) is 4.7 mm, so that's 2.35 mm to be removed from the block at the crank swing, if you maintain the standard clearances. It is little more than that in practise, as the rods are a little broader at the big end bolts. But it is far from being a concern.

The issue is not stroke, as in what crank you use, but bore, as in what pistons you use. There are a number of RB20's around with 4AGZE pistons, they last a long time. Plus RB20 blocks are considered to be the strongest of the RB blocks as they have smaller internals with the same size externals. Thus they are thicker.

As for cams, standard RB26 cams work a treat in RB24's, and they are cheap.

Hope that adds some more

[Cubes]

I would still seriously consider building up a R32 RB25DE motor for the R32.

Work out the costs of buying the GTR crank/rods or RB25 rods/crank any research/dev costs for the machinist then compare it to buying a $900 R32 RB25DE.

If you use the RB25DE you get the benefit of larger valves/ports & larger capacity.

It will still look legal and there is no height issues of the RB30 being 30mm higher.

Its all good to say yer get a set of GTR crank/rods but where will you find them? It is difficult.

Even tracking down a set of RB25DE/T crank/rods may be a little difficult.

Personally I think its a waste of money to buy a set of gtr/25 crank/rods then slap them in to a RB20. Spend slightly more and get your self a RB25DE.

For the run in i'm going to be using the std RB20DET bolts on's. i.e turbo/injectors etc.

I'll post the before and after run of the RB20t running std boost then the RB30DET running std boost. Should be interesting to see the difference. Theoretically the RB30DET should make more power at the same boost as the RB25DE head has less restriction due to its larger valves/ports, as I said before more airflow/power at the same boost pressure. I guess we will see.

Remember also.. The RB30 has the supposively near perfect 1:1 rod to stroke ratio. 86mm bore x 85mm stroke.

[Clint32]

Joel, RB25 crank and rods are fairly cheap and easy to come buy, i sold my set for $250 as i got a rb26 crank and some prepped rods to use. there are also a few places you can get custom forgies for not much more than the off the shelf ones, so basically the cost to build the engine comes out pretty similar, it just depends on what you wont to do.