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Top choice of forged pistons there Andrew. Is that the off-the-shelf RB26 CP kit, or are they customs? I went for CP customs due to 8.0 CR.

I emailed Darius @ CP Pistons at length, and he presented me with quite a few options. I couldn't believe how many different ring combinations they had available!!! Coupled with custom compression ratio, and CP Groove, and lateral gas porting, I had my hands full with choosing the right custom piston for me.

But although lateral gas porting helps achieve a greater ring seal, apparently the ports can fill up with deposits and reduce the efficiency of the porting, and are more suited for race applications where engines are pulled down and rebuilt every few races.

But the off-the-shelf piston, comes with the CP Groove, and raises compression from 8.6:1 to about 8.8:1... Coupled with decking the block/head (increasing compression slightly) and 1.2mm head gasket (lowering compression slightly), I should end up with a net compressoin ratio of about 8.9-9:1 which sounds perfect.

I'm really against dropping the compression ratio to facilitate using higher boost.

I'm really against dropping the compression ratio to facilitate using higher boost.

Yes I must admit I was a touch concerned about the 8.0CR. I was thinking it may result in a lag monster that needed 30psi to produce the goods, but thankfully this was far from the case.

Here's my latest dyno sheet so you can see how my engines 8.0CR, porting and turbo combo actually performs (apologies for the black and white, but I had it faxed to me) The dip up top is due to boost dropping (possible BOV leak issue?)

mypic31.jpg

My combo has damn near the same response as a 9.0CR, HKS 2835R Pro S with manifold and Greddy inlet manifold (same dyno same day). It also made more power on the same boost. A few people were surprised that mine was as responsive as it is. Not only is it 8.0CR but I also run a POS old school plain bearing T3/TO4E. *Note* - the back to back comparo is not the dyno run from above.

I agree that more boost is required (1.3-1.4bar is perfect) to make the numbers on lower compression, and this in turn puts more demand on the turbo.

EDIT: Oh yeah... and I know, I need a set of cams. If someone has a spare set (or even just the exhaust), then feel free to give them to me. I say give, as $ is bloody low atm :cheers:

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