Rb26 Head - What 25 Stuff Can Be Used On It?

[r33_racer]

Ok, here is the predicament. If we are to goto a rb26 head on our new 30 further on down the track. What absolutely has to change in order for it to work. Obviously we are looking at changing the bare minimum, so we can retain the powerfc and loom till we get an autronic later on.

Can we use rb25 ignition setup as we sport s2 coil packs. Are the bolt up patterns the same? My experience with nissan tells me they might.

Obviously we want the std cold side of the head, so is it possible to use our side feed injectors if we can adapt the rail to the 26 plenum? Or is this a big task or not possible incase someone has already done this.

The other things im not sure about are the sensors that are in the plenum? Can they be switched for rb25 ones so we dont have to go rewiring stuff or messing with the loom. Does the throttle cable need to be altered or should it be fine? CAS? are they the same or will something need to happen there?

I cant think of anything else other then we will need a new exhaust manifold.

Any and all help is appreciated.

Cheers.

[discopotato03]

Sad fact appears to be that everything is different except the head to block stud pattern and the water gallery that was modified with R33 RB25 heads . Sorry cam pulleys dimensionally and placement same as any RB DOHC head . Studs are larger diametre as well though I did hear someone say that thin walled sleeves may work . Essentially as long as there is enough support area where the bolt heads/nuts pull down on the top of the head casting I can't see any disadvantage with RB25DET fasteners (over what you use now that is) . Maybe steel wasters with a lip to centre on the stud hole would help keep the stud/bolt on centre . SK ?

The manifold patterns both sides is different , orientation only exhaust side , many changes inlet side though no probs as no one would want the RB25 manifold on an RB26 head . Exhaust side is a pain because there is limited choises with single turbo manifolds particularly if you want a cast name brand ie HKS (known quantity I reckon) . I asked Gary recently if he thought it a practical proposition to weld bosses on the exhaust side of an RB26 head so that it could use either RB25 or 26 type exhaust manifolds . It seems that the right fabrication techniques make this a straightforward operation . I'm also told there are port differences with 26 heads that help make a bit more go .

Lots of aftermarket goodies available for 26 heads , cams/valves/guides/springs etc .

Granted not cheap but better off than other production engines where "works" heads cost house deposits .

Cheers A .

Edited November 21, 2006 by discopotato03

[r33_racer]

I know some people use rb25 11mm headstuds, and if the locking nut position is going to be a problem then i suppose some form of self centring washer would work, we could machine something up for that...thats not really a major hurdle that i would be worried about...more like the injection/ignition side.

A new exhaust manifold isnt an issue either as kyle would make us up one for that. Also i know apexi make a cast manifold that has both rb25 and rb26 holes in the flanges...multipurpose.

Is the injector spacings in the plenum the same as a rb25? So if i could adapt the sidefeed rail to the top feed rail mountings on a 26 would they line up correctly?

So disco you are saying the coilpack placement in the head is different to the rb25 placement? Could you use a rb25 coilpack two piece bracket to get around it if so? Or did they fark it completely so i cant do what i want with this?

[Duncan]

I think you will find almost all of the ECU sensors match the head you are using so you really should change to a 26 ECU.

Neither side manifolds bolt on.

Fuel rail and injecotrs are totally different.

Ignition is different as well if you have a series 2 rb25 head the gtr uses an ignitor pack as well as the coils, not sure if bolts for the coilpacks are the same.

You will need a retune anyway the ECU is pretty cheap compared to the whole project - just remap a standard computer

Its all just too hard.

[discopotato03]

R33 Racer , coil pack fitment not sure though can't imagine why they would change dimensionally . Mine is R33 26 but have not got around to comparing its coils to RB anything else .

Since the car is R33 it would make sense to try and re use the sensors/loom/computer (PFC ?) etc because you already own them . I'm not sure if theres any real value in an RB26 management system unless you opt for twin AFM's (assumes you use MAF sensors) . I think the injector resistance hurdle is more cheaply solved with easily available OEM (not necessarily GTR) resistor packs .

The only really unsolved aspect is the RB26's air temp sensor as in how to get non RB26 ECU's to read it and make compensations if need be . Last I heard Cubes I think had issues with this resulting in PFC electrical repairs . Anyhow no doubt this sensors output could be logged so that any temp/density problems became a known . For those who delve into factry GTR ECU's can you tells us what compensations these ECU's made ?

Cheers A .

[discopotato03]

Probably for the second time but are there any pics available of the Apexi RB25/26 exhaust manifold ?

Cheers A .

[r33_racer]

not that i have sorry. Our tuner used one on one of their customers drift cars.

[barney]

coil packs and the brackets their mounted too should fit in the head, but i s2 gtst coilpacks are different to 33gtr. so they would work while you have the rb25 computer. also cas is the same.

[StockyMcStock]

for the money you'll spend, you could pull the 25 head off, port it heavily and fit bigger stainless valves, put a solid lifter conversion into it and buy some new cams. this is all similar to stuff you would do to the 26 head before you put it on anyway (rebuild it, port it, maybe fit bigger valves, buy big solid lifter cams etc) so you will come out at about the same price, with no dicking around with custom injector rails, loom changes, ECU changes, manifold changes etc.

so my advice, if you really feel you can't get any more power out of it in current configuration (which you sure can!) would be to pull the head off and work it heavily, fit a solid lifter conversion and bigger cams. this will enable you to raise the rev limit, and hence powerband. you could fit a slightly larger rear housing to the turbo too.

i just can't see it being cost effective (in your situation) to change everything to the 26 head. if you were starting from scratch, it would be a different story altogether.

cheers mike

[discopotato03]

Mike I think the castings are different port wise and there are things that can be achieved with the 26 head (port shape) that are not possible with any of the others . I'm told ALL of the valve train components are different in RB26's ie valves/guides/collets/buckets/springs/cams so not cheap to obtain without the casting itself . Also the competition style inlet system is not insignificant for a race car .

The RB25 top end is a saleable item so could offset costs as well .

Probably sounds silly but expensive once and effective ever after , it really does solve most of the limitations of the production 4 valve RB set up and points the inlet tract where it should be .

Cheers A .

[r33_racer]

i know where your coming from neill but the 26 head is born and bred for racing...its better straight off...and as disco said we can sell off the parts were not going to be using anymore. Im in love with the std 26 inlet side...always have been. I cant see why the coilpacks cant be used and cas if its all bolt up....then its just injection which can either be ovecome with using new top feeds and getting the resistor pack for the high to low impedence conversion...or if we get the autronic in time that may not be a problem. new exhaust manifold and bingo. unless im forgetting something.