Cp Rb30\26 9 To 1 Cr Pistons - Valve Cutouts ?

[mambastu]

Hi all,

I recently ordered some CP RB30\26 9.0 to 1 CR 86.5mm pistons and when they arrived I was surprised to find that they don't have any valve reliefs cut into them. Is that correct ? Bit worried as I'll be using 10.8mm lift Kelford Cams with them.

The build sheet is :

http://img861.imageshack.us/i/cppistonsspecs.jpg/

Heres a picture of the pistons :

http://img853.imageshack.us/i/cppistonspics.jpg/

Edited March 12, 2011 by mambastu

[R32 TT]

Correct. Mine didn't either.

[mambastu]

Thats great, thanks for confirming

[dorifticon]

I maintained the 8.5:1 scr on my rb26/30 build and was running jun 10.5mm lift cams, and the pistons had fairly serious cutouts in them. Pics are in this thread:

If it were me I'd definitely be checking with plasticine - once it's all put together and timing set up how you want it of course you would be carefully turning it over to check no interference but you'd want to know what kind of margin there is for stretch etc, espc if you're playing around with the duration of lobles and/or timing with slider cams etc.

But then I'm a fairly risk averse person.

http://www.skylinesaustralia.com/forums/topic/275548-andrews-r32-gtr-bolt-on-build-thread-phase-i-of-my-mods/

[r32-25t]

Actually drifticon I saw your thread and was keen to seen a photo of it with the bonnet closed, just because I'm yet to see anyone else space the subframe and was curious to see how close to flush the bonnet closes,

Cheers Brett

Sorry for the hijack

[dorifticon]

It's not very flush at all - we had to turn up spacers out of alloy, which are 20mm thick. Looks a bit agricultural.

Reasonably confident that it's the "twin turbo" pipe that is causing the problem, rather than the timing belt cover. Im going to a single turbo eventually so assuming I can get a manifold that sits the turbo low enough, it should be possible to get custom piping that clears the bonnet and also allows strut brace to be fitted.

[/hijack]

Actually drifticon I saw your thread and was keen to seen a photo of it with the bonnet closed, just because I'm yet to see anyone else space the subframe and was curious to see how close to flush the bonnet closes,

Cheers Brett

Sorry for the hijack

[R32 TT]

Worth pointing out that the orgininal RB26 pistons didn't have valve reliefs either.

[mambastu]

Just getting ready to build the engine (at last !) and trying to work out deck heights, compression ratio etc.

The build sheet for the pistons lists a dome height of 0.055", does anyone know what that equates to in CC ?

I'm aiming for a 1mm squish clearance so I assume, as I'm using a Tomei 1.2mm 88mm head gasket, they need to protrude from the block by .2mm. Will be CCing the head shortly as its been skimmed in the past.

Cheers

Stu

[R32 TT]

Pretty sure they are a 6cc dome mate.

[R32Abuser]

^^^ +1

[mambastu]

Thanks fellas

[ZT-R]

What cams did you end up running.