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Rb25 Head With Rb26 Internals.

Buckna

By Buckna,
in Engines & Forced Induction

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Buckna Community Regular

Buckna

Posted
Posted

Hey guys.

I have a RB25 in my s14, makes 296rwkw on 16psi with a 3076r, greddy intake, nismo 740cc and motec m48.

I want to keep the rb25 I have, however, I have some JUN cams to suit RB26 (260in 270ex 9.25 lift), I want to use these in my RB25 head. However I'm sure the lift will be too big and it'll bind up.

Now, I have a spare GTR head, minus cams, intake etc. So my question is. Can I just drop the springs and lifter setup out of the rb26 head into my rb25.

Or is there a drama with it? I haven't had a chance to measure the lifters to see if they're the same size or whatever.

And I was hoping someone would have some hands on practical advice/experience on the topic.

I know that NEO heads run a solid lifter setup, but I already have this GTR head so would be nice if this could work to my advantage somehow.

Hoping someone can shed some light on it! Cheers guys.

buckna

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blitzxtr Community Regular

blitzxtr

Posted
Posted (edited)

Why don't you just use the whole RB26 head?

Paul at Red R Racing is currently engineering a VCT kit to run on the 26 head if retaining the VCT is the reason you wish to use the 25 head.

Edited by blitzxtr
Buckna Community Regular

Buckna

Posted
  • Author
Posted

Nah, not worried about keeping vct.

Just want to use the cams, rather than sell them for f**k all then have to fork out extra dollars to buy new ones. haha.

Don't wanna change to 26 head, coz then I have to use different inlet plenum, different injectors, different exhaust manifold etc.

Will the 26 cams work in the 25 head with upgraded springs? I know people use stock GTR cams in a 20det head, which has hydro lifters.

What makes the cams different? between solid and hydro, Realisticly couldn't I just change springs and run the cams? No need to go solid head?

Kruges Explorer

Kruges

Posted
Posted

http://www.skylinesaustralia.com/forums/RB...rb20&st=260

dunno if this helps but if you read it all from memory there is discussion about rb26 cams into rb25 about half way through. i was considering rb26 cams for my rb20 however it seem alot of people have huge trouble getting there rb20s running right after instalation of the 26 cams.

zebra Grand Master

zebra

Posted
Posted

As Ash said, way to much effort for it to work well, the solid cams cause the 25 lifters to pump up and you end up with 0 compression untill they have a chance to get back to normal, you could have the cams reground to suit hydraulic lifters, but you will lose lift and a bit of duration.

Gerg_R31 Mentor

Gerg_R31

Posted
Posted

i've personally tried to convert a rb25 head with all the rb26 internals

rb25 intake springs are the same height and tension and coil bind as all the rb26 standard springs

rb25 exhaust springs are shorter

Rb26 Exhaust valves are sodium filled and are wider, i had to reem and hone the exhaust guides out which left the guides really thin, cant use the rb26 exhaust guides as the guide itself is much wider, cant drill the head to suit incase too much is taken out and the guide wont hold when the head gets hot (more so being exhaust)

both the intake and exhaust valves are another inch longer then the rb25 valves

rb26 installed valve height is aroung 1.550"-1.600" in a rb25 head with rb26 valves 1.850" and 2.050" on exhaust, i couldn't find any springs to suit without a 6mm spacer

then there is the retainers, the rb26 use a cup style retainer to locate the shim that sit under the bucket

the standard shims are around 0.100" thick i needed some that were 0.280" thick

long story short the measurements create head aches, and without going a 1 off spring set there are no springs available

but;

there is a tomei solid lifter set for the rb25 which ive done rb25 cylinder heads at work and converted them to the shim, which has a stem on the inside of the bucket to compensate for the extra space where the lifter was, and the shim to valve clearance needs to be set on that (wish i knew these existed before i started the work on the head)

you would also need to see if the valve springs will suit the cams

hope that helped

Stronzo Collaborator

Stronzo

Posted
Posted
rb25 intake springs are the same height and tension and coil bind as all the rb26 standard springs

rb25 exhaust springs are shorter

rb25 EX valve springs are longer than IN (free length 45,58mm EX and 39,4mm IN)

rb26 springs free length is 46,54mm both IN and EX.

SD-5 page of service manual.

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