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RB30 Block / RB26 Head - Machining requirements


Guest daewoo

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Hi all,

 

I have been talking to lots of people here in the land down under. Everyone says that fitting an RB26 Head to a RB30 Block requires major maching work, where the RB25 Head is a straight fit.

 

Anyone know exactly what is required? How much advantage (other than braging rights) are there between the two heads?

 

RB30s are a dime a dozen here, imported heads are not.

 

Cheers,

Daewoo

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Not many are doing the RB30 conversions here in the U.S. You will find more information on Skylines Australia,

http://www.skylinesaustralia.com/forums/index.php?showtopic=15420

 

I am still in the assembly phase of mine. The only additional machine work required for the RB26 head on the RB30 is tapping out the block for larger diameter head bolts.

One minor thing, you want to block off the rear oil feed to the cylinder head on the block as well.

 

Cubes made a PDF file about the RB30 conversion.

http://www.geocities.com/rb30_twincam/

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Stealth-z is right...ive done a 26 and a 25 head and the 26 head requires the head stud threads in the block to be drilled and tapped and the rear oil feed to be blocked..the 25det head needs the vct oil feed to be blocked and an external feed to be drilled and tapped if you want to run the vct..the 25de head bolts straight on..25 de and det heads have the correct size studs to suit the rb30 bottom end..

PERSONALLY i dont think there is that much advantage in a rb26 head other than the plenum and solid lifters,and you will have real problems fitting the stock crossover rb25 plenum (in a s30 body if thats what you are doing)

I have a rb25det head on a stock rebuilt rb30e bottom end with a greddy plenum and im making 548rwhp on 15psi with a gt35r

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PERSONALLY i dont think there is that much advantage in a rb26 head other than the plenum and solid lifters,

 

I don't know any numbers but I read something on a site about this subject and they said that the rb26 head flows mutch better then the rb25's.

correct me if I'm wrong.

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Thanks Gents,

 

I hope to fit this to a S30 Right Hand Drive 240z if I can find one. The car will be for racing on dirt and circuit.

 

I am sure tha most questions have been answered a hundred times here and on skylinesaustralia.com (there is a thread there on the RB25/30 running to 225 pages). There seems to be a lot of info on the RB25 Head, but none on the RB26. I had been told it requires a lot of machining, but from what I could tell, the only difference (between RB25-26) was re-drilling and taping the head studs.

 

I would like to know if there is any HP advantage between the two heads, or is it all in the turbos?

 

Cheers,

Daewoo

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I don't know any numbers but I read something on a site about this subject and they said that the rb26 head flows mutch better then the rb25's.

correct me if I'm wrong.

You are probaly right BUT how much power can you possibly want in an s30??im making near 550rwhp on 15psi without nos.my car is my daily driver and i drag race a bit. im am CERTAIN that i could make 650++rwhp if i ran 20psi and a shot of nos.The torque of the rb30 is atronomical(couldnt quote off the top of my head)..Im still running just linished stock rods,balanced stock crank,stock cams etc.so there is plenty of development left in it yet.

Basicly what im trying to say is you will easlily make the all the power you can possibly want out of a rb25 head and i think the extra $$ you will spend on a 26 head and drilling the block would be better spent on chassis/suspension work etc..thats my opinion anyway..

By the way daewoo im just up in newcastle!!

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Thanks RBS30,

 

You are probably right but, I will be getting my brother who lives in Japan to source parts and send them to me. He doesn't kow much about cars, so I think asking him to organise a half cut or complete wreck would be a bit much.

 

Therefore, if I am only asking him to get a head, I was wondering if it will be just as easy to ask him to get an RB26 head.

 

Do you mind if I PM you with some questions so as not to waste peoples time reading the forums?

 

Cheers,

Daewoo

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  • 2 weeks later...
I don't know any numbers but I read something on a site about this subject and they said that the rb26 head flows mutch better then the rb25's.

correct me if I'm wrong.

 

All of the sites that I have seen with actual flow #s, come up with nearly the same flow on the 25 and 26 heads. The ports are almost identical if you look at them side by side. The RB25 intake is actually larger on the opening than the RB26, due to a larger cut for the injector spray path.

 

As far as porting, they are about the same as well. I cut up an RB26 head with a band saw, which showed the ports from the water jacket side, to see how far you can port it, and it looks the same at the RB25 head.

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