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Help Getting The Right Compression For Rb26/30?

wsln33

By wsln33,
in Engines & Forced Induction

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wsln33

Posted
Posted

Ok guys, i need some help if you are good at working out compression ratios. These are the facts im working off -

- gtr head approx 62-64cc so i used 63 for my calculations,

- head gasket cometic 87mm and 0.051thou (i worked out 7.5cc),

- cp 86.5mm flat top pistons set up at 0 deck height for the right squish ( i got 499.506cc using 85 stroke and 86.5 bore).

With this i get close to 8.1? Is this right or am i missing something? Im after a compression ratio of 8.8. What will i have to do? shave the head?

Adriano Grand Master

Adriano

Posted
Posted

You need to cc the head to determine the exaact size, as they do vary, and a small difference here makes a big difference in the comp. You could deck the block to increase the comp, but i wouldn't go smaller than 30thou squish on a street engine, the rest you will have to take out of the head, thats the problem of using flat top pistons, dome tops are heaps easier to get the higher comp.If you use a 1mm head gasket and 10 thou off the block, you will lose about 3cc, probably need to shave the head 15-20 thou also, but measure it all first, guy a burette and dummy assemble it first before you get the deck/head machined.

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