Rb26 Crank And Pistons Into Rb25

[Adz2332]

Hey all

Currently stashing rb25 forged stuff aside for when my car goes pop...

I know it can be done but what are the benefits of using the rb26 crank and forged pistons or a rb25 crank and forged pistons?

Or even what are the negatives??

[GTSBoy]

Weeeeeeeellllllllll..........100cc extra is the benefit.

Need the rods too, obviously enough. Neo 25s already have those.

[Adz2332]

well yer thats what i thought, but then why doesnt everyone do it when rebuilding a 25?

[XKLABA]

No, rods are same length, 25-26-30 all have interchangable rods, 26 rods are stronger , extra 70cc and the pistons have a 2mm lower comp height and are lighter

Edit; Sorry, its 1.5mm, the 30 is 2mm

[GTSBoy]

Ah, yes, valid point about the rods being the same. I've made that mistake before.

The reduced compression height is a bit of a bitch, and probably the main reason why it doesn't get done so often. Need different pistons or massive boost.

[XKLABA]

The reduced comp height is to account for the extra stroke, the GTR was originally built with a 25, but cause of the weight of the thing they increased the capacity to over 2.5 putting it in a different class and did so increasing the stroke and corrected it by lowering the comp height

I have way way to much time to kill

[Adz2332]

interesting.... well put simply this seems like the way to go...

the hoarding of parts continues...

[GTSBoy]

So once again I am shown to have not thought before posting!!

[MJTru]

I have always wanted to try this. But just ended up going with all new forged parts.

[Adz2332]

what crank did you use mate?? is it true that you cant get forged rb25 cranks?

[zebra]

Sure you can

would just have to pay through the nose to have one made

[zebra]

If you were going to do it that way

have it made with SBC little journal 2.1" big ends and open up 11ty different rod options, use a custom piston with a nice and low comp height and heavy wall tool steel pins.

[Adz2332]

Sure you can

would just have to pay through the nose to have one made

this is the main reason im thinking rb26 crank

[XKLABA]

Pfft, just get a BC 2.9 stroke and enjoy the torque

So once again I am shown to have not thought before posting!!

Trust me ya get use to it enventually

[r32-25t]

Rb30 rods are longer then 26/25 rods and the Gtr was originally built with a 2.4 but then increased to 2.6 because it was a dog

[XKLABA]

Wow, schooled, I'll have to go back and have another look cause I'm sure I have 26 rods and 25 pistons in my 30 block but now you have got me thinking, I might have that wrong

I'm also sure it was 2.5 as 2500cc was the class limit and cause of the weight of the 4WD system they increased it 70cc and went up a class, been a long time since I read into it, will try and find it

[XKLABA]

No I was wrong, it was a 2400cc to race in the 4000cc class ( x 1.7 for forced induction ) but the addition of the 4wd made it to heavy so they went up to the 4500cc class, and am still it sure what i was thinking of and where I got the 2.5 idea from

And it is the 25-26 rods that are the same lenght, 30s are longer, massive fail on my part

[GTSBoy]

I just had a look at the wiki page on the R32 GTR. The limiting factor was the 10" wide tyre required in the 4000cc class. Too skinny to give the performance they wanted RWD, so they added AWD gear the weight of which required that they add capacity to step up to 4500cc. Legend created by process of staggering evolution.

[XKLABA]

So once again I am shown to have not thought before posting!!

I just got that exact feeling

[1400r]

ignore the still learning driving of my mate back then

Japanese built 2.7lt motor is still going now in a s14 in WA that's for sale

after surviving 3 or 4 different chassis's

how many motor's built here are still alive 7 years later

this thing also ran a f-con when it first came over (i.e untunable)

Edited June 10, 2014 by 1400r