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RB25DET Head Differences

blind_elk
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blind_elk Grand Master

blind_elk

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A long time ago, I fitted a RB25DET from a Stagea into my R32 GTS4. I've recently started wondering if there are any differences between the Stagea head and a GTSt head - eg, cam profile, cam timing, chamber shape / size, inlet / exhaust port shape / size.

Is it worth getting a GTSt head, or just GTSt cams, or it doesn't matter?

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Rusty Nuts Experienced

Rusty Nuts

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4 minutes ago, GTSBoy said:

There's no differences in any of the vanilla RB25DET heads

Theres the answer, The R33 RB25 non turbo and turbo heads are essentially identical. The valve springs cams, valve size, port size etc are identical. These were used in series 1 Stagea. Neo is another story

Edited by Rusty Nuts
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Rusty Nuts Experienced

Rusty Nuts

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2 hours ago, blind_elk said:

Is it worth getting a GTSt head, or just GTSt cams, or it doesn't matter?

It doesn't matter if series 1, Neo turbo has higher lift exhaust cams.

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Rusty Nuts Experienced

Rusty Nuts

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1 hour ago, GTSBoy said:

And the next point is that you shouldn't put a Neo head on a vanilla block without considering the effect of 15% less volume in the combustion chamber.  Alright if you plan on using E85 only.

Sorta correct! all 33 series 1 and 2 and neo blocks are 75T casting No. blocks so are the same! All decompression is by piston fitted.

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Rusty Nuts Experienced

Rusty Nuts

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1 hour ago, Rusty Nuts said:

Sorta correct! all 33 series 1 and 2 and neo blocks are 75T casting No. blocks so are the same! All decompression is by piston fitted.

Should also add combined with different crank throws and different conrods

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GTSBoy Grand Master

GTSBoy

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Um...that's exactly what I meant.  but when people are talking about swapping a head on to obtain some perceived advantage, it is almost always the case that they are talking about putting it onto their existing block, including the pistons.

So I was 100% correct.

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blind_elk Grand Master

blind_elk

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Thanks for calling a truce!

It is a S1 Stagea engine (probably equivalent to a S2 GTSt engine). Has VVT. Has been rebuilt with forged pistons.

Think I'll save some coin and not do anything to it ?

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Rusty Nuts

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9 minutes ago, blind_elk said:

Think I'll save some coin and not do anything to it ?

Wise move chum, there was a big sign in a workshop I worked in, that said,

"Speed costs money, How fast do you want to go."

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GTSBoy Grand Master

GTSBoy

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1 hour ago, Rusty Nuts said:

 A Neo head on your so called vanilla bottom end would achieve same compression as standard neo turbo and they dont need E85 is what i'm saying.

Um . No.  Just no.  Neo DET head has about 51cc chamber volume.  Vanilla has about 62 or something similar.  Jam a Neo head onto a vanilla bottom end and the compression ratio goes through the roof.  This is a known fact.  Neo pistons have much lower crown height because the chamber is flatter because that's one of he big changes made to make the Neo heads (on various engines).  It was about reducing the surface area of metal facing the combustion event.

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