rb25 block + rb26head - info thread

[Kaido_RR]

I have post this up a few times and been majorly flame for it, so why am i posting again becuase i want to get people comments on the idea

Now the idea is basicly putting an rb26 head onto an rb25 block. Now i know it can be done and i also belived that is a farily common job and it isnt a hard one (this info is coming from a mag i read i belived it was zoom or something similar)

It seems that a r32 gtr in perth is running an rb25 block with 26head. Now i guess the pros to this sore of job would be the cams, turbos (2 ), gtr plenum (6 throller forward facing) and just the overall advance in the head compare to the 25.

now i know not alot so lets work this out price wise

Source from jap r33 rb26dett head (with fuel rail, plenum etc etc) without turbos $1500 (average kms 70,000 to 80,000)

(this price was given to me by a local shop which can source the part)

now then i would need the turbos (and everything else that would go with it dumps etc) which would add up to $.... (no idea)

Now in the mag they said it was pretty much a direct swap and talking to SK in the past he said that if you "wish" you could tap the bolts as they are 1mm larger but it wasnt needed.

now my question is would you need to some machine work to the head and the block before u put it together. also if it is a direct swap ti would be as simple as removing only head + turbos, dump, ic and then install the rb26 head + turbos + fmic piping etc etc. Which sounds like a job that could be done in a backyard over time.

Now once the head is on, im guessing that a ecu would need to be address. as im guessing there are senors etc in the head which would be different from the 25 to the 26 so possable adding aftermarket ecu (pfc) or moding a gtr ecu to suit an gts-t (i belived this can be job and a workshop in perth did it)

Now as the topic states this is an info thread; i dont want it to become full of flames and have it closes or delete. so could people plz just add there 2cents if they know anything about doing such thing

(and for all the perth users that know me and i ulimatly be the ones flaming like the last threads, plz i do not wish to do such things to my skyline, im just mking a thread to get info and share that info with other skyline users, so if u have nothing nice or anything related to the topic plz do not post)

Thankyou Michael

[Warpspeed]

For what you are asking there are basically two different types of RB blocks, one uses the variable valve timing on the inlet cam, and the other does not. These two different blocks have slight differences in the front right hand corner, which concerns how the oil drains back from the VVT to the sump, and the nearby water passages in the same area.

Very early RB25 blocks did not have VVT, and neither does the RB30, or the GTR, so heads and blocks all fit straight together.

To fit a GTR head on a later RB25 VVT block requires some easy modification of either block or head. Apart from that it all goes straight together using the original 10mm RB25 head bolts. Or you can tap the block for the 12mm GTR head bolts if you want. The locating dowels are the same in all RB engines, no changes are required.

Your best bet is to buy a complete RB26DETT and fit the crank, rods, pistons and oil and water pumps. But use the original RB25 block and sump.

Or you could buy a blown up RB26 and just use the top half on your RB25 bottom half. You should be able to find an absolutely complete RB26DETT that has spun a bearing or has several cracked pistons (from detonation) for maybe $3,000. The top half will likely be quite o/k.

After you have sold your RB25 top half to one of the RB30 Commodore guys, it should not work out too bad if you do it all yourself.

[Kaido_RR]

thanks for the reply warpspeed,

how can i tell which rb25 engine i have? my car is an 1993 gts-t (built month the 9 i think)

i was always under the impression i had vvt

[Warpspeed]

Have a look at the two cam wheels on the end of the cams.

If they both look the same, there is no VVT fitted.

With VVT engines the inlet cam wheel has a huge "nose" fitted and looks quite different to the wheel fitted to the exhaust cam.

[Kaido_RR]

Thank Warpspeed,

just had alook and it does have VVT

[RB30-POWER]

If you bolted the RB26 head to the RB25, it should be able to rev a little harder having a slightly shorter stroke that the RB26 wouldn't it?

I know it would be neglible, and you may not make the same power anyway due to the smaller displacement, but still...

[Kaido_RR]

rb30-power, that was another point i was looking at being able to rev the car alittle more and with the increase in power (from the twin turbos) the car should be able to make some more power and hopfully the lag wont be a big deal as it will be gtr cams

[N I B]

The GTR with a RB25 GTS-4 block and GTR head was done because the class the car was racing in had a 2.5L limit at the time and the GTR block was stuffed.The rules changed and we have gone full RB26 now.VVT is worth keeping.

[Kaido_RR]

steve, im guessing its not possable to run the 26head with vvt. can i ask why its worth keeping?

[N I B]

HKS have a VVT kit for 26 heads now but cost is high.

If you fit a Greedy intake and cams to your 25 head it will be cheaper than going 26 head and give you a broader power curve.Get a 25 and 26 head flow tested and be suprised. Dont spend money you dont need to.

[Kaido_RR]

thanks for the info steve, but im just after some info

what is the draw backs from putting the 26head onto the 25block? will losing the VVT make that much of a differences in power, responds?

[N I B]

Ifyou are planning a big budget build with every possible option then a 26 head can be a minor help but chasing a budget street build its a bit over the top as a new turbo etc will give huge gains for less as a 26 head needs other changes to do right,even the head bolts are thicker on a 26 and the combustion chambers are different, I think i'm

the only shop in WA thats done it and it was only for the class reason.

[Warpspeed]

Steve is right, the GTR head has the same ports, valve sizes, and combustion chambers to the RB25. In other words the GTR cylinder head has no more power in it.

What makes the GTR so good is the superb six throttle body induction and the twin turbos. But a Greedy inlet manifold on an RB25 would come mighty close for a lot less cost and trouble.

The VVT is only there to enable the RB25 to pass idle emissions and still make reasonable power. The GTR can pass easily without VVT simply because the six throttle bodies are so close to the inlet valves. VVT is for emissions, not power !!!

If you put decent cams in an RB25 and get rid of the VVT it will go much better, but it could never pass idle emissions like that.

If VVT was there for top end power, why was it not fitted to the GTR ? It would have cost them nothing to add it. The obvious answer is that it was not required and adds nothing to performance.

[N I B]

VVT gives better lower +mid range power.

We remove the 6 throttle bodys with great results anyway,We have demo cars to prove it.

[Warpspeed]

Individual throttle bodies give vastly improved throttle response, are much more cam friendly, and give much cleaner idle emissions.

A large single throttle might give you a poofteenth more power right at the extreme top end, but is a bummer for drivability. Drag racers use large singles, road racers use individuals.

Maybe all the Formula one guys are complete dummies. Maybe they should use a big single eh ?

If VVT was the total answer, why did not Nissan use it on both the inlet and exhaust cams of the GTR ? They obviously have the technology to do it, Maybe they are complete dummies too ???

[N I B]

You would be suprised how wrong you are its a shame your not over here to test one.

[Roy]

How are you testing it? On a dyno, road, track with data logger.

[nv033]

A 25 head has hydraulic lifters...26 solid... fair enough the ports may be the same size and if ur revving to 7,000rpm they may be comparable....

what if ur revving to 8500rpm...the rb25 head i dont think will be as efficient as a 26....

cost benefit analysis.....if ur motor is apart, ur a bit lost if u bought a greddy manifold for $1000 and put it on ur rb25 then some decent cams for $1000 when a 26 head is $1500....its got the manifold, bigger cams, solid valve train (which u can pay tomei $1500 for to do the conversion to a rb25)

i would personally put the 26 head on if uve got the opportunity...... in regards to combustion chambers being different i not sure about that... maybe some1 can fill us in with some more information to whether it is possible and what to do....unfortunatly we do not all live in perth and have ur workshop at our disposable...so instead of bagging out the potential modification maybe input into it....

i believe the exhuast valves on a rb26 is larger warpspeed and i do agree with ur vvt theory....how many ppl really care how much power they have before the vvt switches off?? lets say approx 4,500pm....a 10-20 rwkw difference at this rev does nothing for me? then again its an adrenalin rush for others :headspin: :headspin: :headspin:

[Kaido_RR]

edit:was miss inform

[Kaido_RR]

nv033, the more i think about it the better the idea seems to me, thou if i do go ahead with it, it will be alone term project so i will pay the parts over a perdio of time then hope to install it in a few weekends or weeks