like it says what HP could you expect to gain from an RB25 head conversion alone???? and what are they worth?

I heard that they give they give it an extra 30% gain on top of outright power.

thats a fair bit, anyone know what they are worth????

buy an RB25DE engine for about $750, that will have most of the parts you need for a conversion. heres an old zoom mag article where they fitted an RB25 head to a R31, with no other mods, before and after dyno charts. check out sites like : http://trinity.frontierisp.net.au/~rowan/twincam.htm a step by step guide with prices and parts required Some original photos have not been recovered yet.

As you can see above you get about 103rwkw with a straight head swap, but the compression ratio is a little low for a NA motor (great for turbo application though) about 8.3:1 If you also fit the RB25DE pistons into the motor it will raise the compression ratio to about 10.0:1 which is great for an NA and you may spin up to 160rwkw with that combo. Mick

yeah thanks, thats a pretty good power gain for an NA, actually looking at putting one on my trubo in a while, so just doing some homework at the moment. besdies forged pistons to get the compression ration down and a aftermarket ECU which i already have andhow is there anything else which i may need, anyone hear actually done it?? thanks for the replies guys.

There was a Vl in Street Commodores recently that has done the conversion. I think it was 2 issues ago.

the more advanced combustion chamber design also means u can run more boost at a given CR compared to a rb30 head. (rb25det's compression ratio is 9.0 stock)

ok then thats good to know. Keep the info cominng guys, any comment welcome

If you do the conversion, always try to go for the non-VCT head, as it is a straight bolt on proposition. It also has more aggressive cams. The VCT was only to change cam timing to meet emission standards. Mick

gus mentioned forged pistons, but is it possible to just use the RB25 pistons directly? Do they fit ok into the rb30 block? Buying an engine right out and stripping what you need from it if so would be a good way to go I'd imagine, pistons and head and all ..

RB25 pistons will fit (same bore size as RB30) as long as your block has not been bored out.

that link i posted above tells you all the bits and peices you need, but it doesnt seem to be working for me for some reason - anyone got a link to that page that works?

heres the page, although its an old version, the link above was updated with a fair bit more info and prices etc. dunno why it wont work! http://www.meggala.com/RB30head.htm

RB30-Power what do you mean when you say that the non VCT head is more aggresive? I think it depends how you tune your engine more likely, or is it just like fuel injection where everyone avoides it because its new/unknown? VCT can be tuned to be just as good if not better then a high hp cam. Otherwise why would a car such as a lamborghini use 3 phase electronicaly controled VCT? I know you cant compare engines as such, although you have to look at the principle VCT.

he means the RB25de head has more aggressive cam profiles compared to the RB25det head. The NA RB25de has higher lift on the cams.

So then when air is forced in, less agressive cam profiles would be more efficient as the air has less trouble getting into the cylinder when forced in. I suppose the timing angle of the cams would be different as well for both exhaust and intake? (As well as for n/a and forced RB25 heads)

say i was going to use the pistons out of the RB25 motor, i take it that i would need the turbo pistons (BR25) to get good CR?? or is there no diference between the CR's of the turbo and NA RB25's??

There is a difference, after conversion. turbo give 8.3 na give 10.5ish Do a search in the forums?

go to www.skylinesaustralia.com (http://www.skylinesaustralia.com) - forced induction performance find the thread "R33 RB25/30 conversion" of something like that... 20+ pages of very useful information and will help you to understand. i highly reccommend you go read it or else you are wasting your time.