Rb25 Vs Rb26 Head - Anybody Got Any Practical Knowledge On Whats Better?

[Guishnu]

Im REALLY sorry for spamming this section with questions - i didn't know whether to put this in my other thread or start a new one... so i started a new one. Appologies if this is wrong mods

ANYWAY!

Does anybody have any advice on what the advantages are of running an RB26 head over an RB25? I already have a 25 head i can use, which is easy to do - however im a big believer in "do it once, do it right" mentality. Will an RB26 head make a big difference in throttle response and overall power?

Has anybody done both and driven both back to back?

Thanks in advance

Chris

[Dale FZ1]

Having seen both on a bench, the 26 offers bigger exhaust ports, and allows for the fitment of significantly higher lift cams vs the 25 head. Didn't measure the valve sizes, but exhaust valves in the 26 looked maybe +1mm as well.

To me, that means the 26 head is a better platform to make big power. That said, there are plenty of 30/25 combos producing ~ 300rwkW and not revving hard to do it.

While I think the 30/26 is a better thing, whether you get much chance to demonstrate that will depend on where you run the car and how much $$ you pour into the build. eg. for an 8000rpm 30/26 you'd be wanting forged rods, very good crank balance, very good harmonic balancer, and oil pump. The bills add up quickly if you want to spin the engine hard.

[2BNVS]

having both although havent done the final tune with th 26/30. if u wanna go more extreme go the 26/30 ( be prepared more costs involved) for a less extreme but still great set up go the 25/30 ( mind u less extreme is nothing to be shy of, i ran 352rwkw with my 25/30) that was with some serious headwork to fit big cams, solid lifters, etc etc, where as the rb26 has the potential already there ready to go

I also keep the 6 throttles, compared to a mates with almost identical set up i do find mine slightly more responsive than a massive TB.

[Al]

I know that the rb25 head can flow big numbers with tomei poncams, extensive head porting and tomei valve springs.

My mechanic has achieved 484rwkw using the above mods to the rb25 head; that's on C16 race fuel, 35psi boost, no NOS, and using an rb25det (not an rb30det). I myself have done the above and have made 325rwkw, using a GT30R (500hp) turbo, 18psi and on pump fuel (BP Ultimate).

Having said that, it would probably be cheaper to sell the rb25 head and buy the rb26 head. That way you will also have the benefits of solid lifters, be able to run bigger cams and multi TB's.

The major cost is in the porting, as a good head porting job can cost you in excess of $1600.

[r33_racer]

sodium filled valves std.

[Phobic]

im going down the 26 head path, hopefully going to pull some big numbers with all forged internal and pretty parts to support and keeping the 6 t/b's as someone mentioned to keep response but am yet to see what numbers im going to pull