Head chamber CC, RB26GTR and RB25DET

[Chris Wilson]

Can someone post up standard head chamber capacities for stock RB26GTR and RB25DET cylinder heads please? Thanks.

[GTR-Ben]

63cc for both.

Although I have ran into quite a few low compression heads on GTRs.. this is obvious by the large step in the combustion chamber.

[Sydneykid]

Between 62 cc's and 65 cc 's, they vary from model to model.

[ace_nz]

70 according to the wiseco information sheet, all the ones ive ever done have been at least 66, theres an obvious difference between 25s and 26s the 26 chambers are alot deeper, all these 63cc rb26s must have been milled heaps to get them that low, if you do a comp ratio calculation using 63cc chambers youll end up with higher than the factory 8.5 to 1.

[Sydneykid]

The only one I have seen over 64.4 cc's had deep seated valves. Somebody had been doing a bit of amature valve seat grinding.

[Cubes]

My R32 RB25DE head was 62.2cc's.

[ace_nz]

how can 25 heads with comp ratios of 9 to 1, smaller crown on the piston and a shorter stroke have the same cc chamber as 26 heads that have 8.5 to 1 comp ratio, if the stroke of the 26 is longer and the crown on the piston is bigger then with the same chamber volume the 26 comp ratio will be higer than 9 to 1.

[Chris Wilson]

ace_nz, this was the thinking behind my question. I have a stock Nissan RB26DETT piston, and a stock Nissan RB25DET piston here on my desk, the crown protrusions differ as you say.... Hmmm. I am asking this as i have been offered an HKS 2.8 stroker kit, brand new, at a good discount, and am trying to work out the compression if I fit this kit into my RB25DETT block with RB25DET head.

[Cubes]

When you do work it out please update the thread as to help SAU be the rich source of information it is. Well some times, not in this case.. well maybe, the thread isn't dead yet.

[N I B]

Arias Pistons for RB30s with twin cams head have 2 part numbers ,one for 25 head and one for 26 head.I have to CC pauls head and a stock GTR head this week as he has an RB26 crank going in to his RB25 and i need to work out the pistons i need to use.Will post the details then.

[pnblight]

one thing you guy might have over looked here it the piston to deck hieght of block the head and piston from 25 and 26 could be just as you said but if the piston to deck height could be quiet different (i dont know this just idea that could expain the problem)

[ace_nz]

theres slight variations between deck heights on all engines but not enough to vary comp ratios alot. Idealy you want 40 thou piston to head clearance to optimise squish, which is mechanical octane despite what some people might tell you.