Rb26 Crank In A Rb25

[dori34]

hi guys, its time to come to rebuild the motor.

the path i am going is to rebuild the 25 block with 26 internals (crank/rods/pistons - i manage to score the bottom end for real cheap so its a cheap way to stroke it & be stronger at the same time)

now i need info from ppl who has done this and what complications they came across if any or any help/tips that they can provide.

I've searched on sau, skyline owners & google and have seen a few ppl do it with success but there were really no technical answers, just yes it will fit but like anything there is always a hurdle to jump over.

the head ill be using will be a R34 RB25 Neo which should work fine. Would the pistons clear the valves & not smash them?

RB25 stroke: 71.7mm

RB26 stroke: 73.7mm

difference in stroke is 2mm so would i assume that by adding 2mm thicker headgasket will make things clear or am i wrong?

parts list include

R33 GTR crank

R33 GTR rods with arp bolts

ACL 86.5mm pistons

cometic head gasket (not sure on size?)

any help much appreciated.

[Swiper the Fox]

hi guys, its time to come to rebuild the motor.

the path i am going is to rebuild the 25 block with 26 internals (crank/rods/pistons - i manage to score the bottom end for real cheap so its a cheap way to stroke it & be stronger at the same time)

now i need info from ppl who has done this and what complications they came across if any or any help/tips that they can provide.

I've searched on sau, skyline owners & google and have seen a few ppl do it with success but there were really no technical answers, just yes it will fit but like anything there is always a hurdle to jump over.

the head ill be using will be a R34 RB25 Neo which should work fine. Would the pistons clear the valves & not smash them?

RB25 stroke: 71.7mm

RB26 stroke: 73.7mm

difference in stroke is 2mm so would i assume that by adding 2mm thicker headgasket will make things clear or am i wrong?

parts list include

R33 GTR crank

R33 GTR rods with arp bolts

ACL 86.5mm pistons

cometic head gasket (not sure on size?)

any help much appreciated.

i would assume you are thinking about using GTS-t pistons?...the easy way is to just use RB26 pistons as the pin height is correct but you will have to run a thicker than std head gasket as the NEO chambers are smaller. Should be able to work out the static comp on paper and you will be able to see the difference each size head gasket makes.

Edited May 20, 2010 by Swiper the Fox

[Aberax]

I too am looking into this after reading an article in HPI. A member on SAU "GTS-t VSPEC" from the WA Section has done it, I have gotten in contact with him via pm, here is a bit of info he has supplied;

We took the easy way out and used an R34 GTR crank an then used oversize pistons to give us 2.7L. Its amazing that more people don't use GTR crank, pistons and rods as they're virtually a straight fit.

The R33 GTR crank is fine, but you'll need something like the JUN Crank Collar to avoid the chance of damaging the oil pump (the R34 cranks have a better attachment to the oil pumps).

You could go standard RB26 pistons, but then of course you'd only get the standard stroke. For the money it's hard to go past forged pistons, probably just 1mm oversize.

I think my headgasket was 1.2mm, but for me it was important not to drop the compression ratio too low, as the 9:1 ratio on the 25's is pretty much perfect.

Mind you, I was asking about stroking the RB25 into a RB27, not sure this info applies to the NEO, as I was reading somewhere recently that there is something smaller on the head...however don't quote me on that.

[Swiper the Fox]

I too am looking into this after reading an article in HPI. A member on SAU "GTS-t VSPEC" from the WA Section has done it, I have gotten in contact with him via pm, here is a bit of info he has supplied;

Mind you, I was asking about stroking the RB25 into a RB27, not sure this info applies to the NEO, as I was reading somewhere recently that there is something smaller on the head...however don't quote me on that.

Yes...as stated above the chambers are smaller...hence the static comp. increases as an engines chamber cc decreases.

[NutR33]

Most of the parts are interchangeable.

As swiper said, use the rb26 pistons (or forged pistons to suit an rb26) as they have a different pin hight to allow for the longer stroke.

You can use the rb25 rods as they are the same length and bearing size, but the rb26 rods are stornger.

rb25 balance and crankshaft cambelt drive pulley fit the rb26 crank but you need to buy the rb26 crank balancer bolt and washer as they are a differnt size thread.

rb25 flywheel/clutch will fit the rb26 crank.

Only clearance problem i had was the oil squirter cut outs in the pistons were not big enough, 10min with a die grinder and that was fixed, but i believe that was just the brand of pistons i used.

Cheers

NutR33

[N I B]

Done this many of times. RB26 Crank, Rods and Pistons are a simple upgrade with no extra work required. Can not use 25 pistons.

[msports180]

Hmm interesting... So this will give you a RB27? with what size pistons? Or is that with stock?

[D_Stirls]

It'll only give you 2.7 because of the over bore. If you have a standard bore it will be exactally the same displacement as a standard RB26 as both the 25 and 26 have an 86mm bore.

Just wondering why it was said that the R33 crank would need a crank collar. I was under the belief that it was only the 89-92 RB26 cranks that had the short oil pump drive?

[msports180]

But the 26 crank has a longer stroke?

[N I B]

Yes 26 stroke is longer than 25, The reason why you end up with an 2.6 is using stock bore size.

Only difference between RB25 and 26 block is the head stud size, VVT oiling and lower block face for the 4WD sump basically everything else is the same give or take a few castings for the Twin turbo oil drains, and oil grooves under main bearings etc.

[dori34]

Fantastic news, thanks for all the info guys.

Sorry i should've mentioned that i'm going to be using RB26 pistons not RB25

AFAIK as well the R33 GTR onwards had the longer nose crank so won't be needing the crank collar, is this correct?

he R33 GTR crank is fine, but you'll need something like the JUN Crank Collar to avoid the chance of damaging the oil pump (the R34 cranks have a better attachment to the oil pumps).

- this might be a printing typo as i've researched and only early R32 GTR cranks need it.

Technically it will be stroked so it brings the cc up to around just below 2.6 just like a RB26.

[Adriano]

Check your oil pump drive, as even the longer r33 ones are prone to wear. Just bear in mind you will be better off with lower comp rb26 pistons than fitting a thicker headgasket to give the desired comp. What turbo are you planning on running?

[dori34]

Adriano; R34 GTR BB turbos. cheers for the info!

[discopotato03]

By my calculations an 86.5mm bore and 73.7mm stroke gives 2598cc capacity .

I believe many consider 87.5mm the bore limit on an RB block and with this and the RB26 crank stroke the capacity is 2659cc .

At 86 by 85 the RB30 comes out at 2962cc std . If your states legislation allows don't you think this would be an easier way to go ?

If you only spent money on two areas in an RB30 - crank collar and coated std piston crowns the build would still be reasonably affordable .

A .

[James_03]

yeah dirty 30 it.

[dori34]

narh, not going 30 bottom end.

[XRATED]

Definatly keep the 25 and throw the 26 rotating assembally in it. Correctly preppared and assemballed the 26 gear is good for 400rwkw, is lighter than a 30 rotating mass and cheaper/easier if your building a motor anyway.

Also crank collars are so cheap- you might as well have on installed.

Shot peen the rods and intall arp bolts.

Ceramic coat the piston crown and teflon coat the skirt.

Any you'll end up with a really nice, inexpensive bottomend.

[Red R Racing]

Definatly keep the 25 and throw the 26 rotating assembally in it. Correctly preppared and assemballed the 26 gear is good for 400rwkw, is lighter than a 30 rotating mass and cheaper/easier if your building a motor anyway.

Also crank collars are so cheap- you might as well have on installed.

Shot peen the rods and intall arp bolts.

Ceramic coat the piston crown and teflon coat the skirt.

Any you'll end up with a really nice, inexpensive bottomend.

sounds like the old bottom end that Paul used to run 10.3's with. 450+ though

Edited May 24, 2010 by Red R Racing

[dori34]

Thanks xrated, very constructive reply. is a crank collar needed even tho it's a 33 gtr crank? Build will be starting shortly so we'll see how it goes. appreciate all the help

[N I B]

No you wont need the collar with an R33 GTR Crank.