hi all

id just like to know how do you calculate how much needs to be shaved off a head to reduce the CC and in turn increasing CR.

ive CC'd everything, the pistons are 14cc, head gasket 3cc (.6mm GX) and head 26cc. that gives me a CR of about 8.65:1, im chasing about 9 or 9.5:1.

engine details are A15 with new standard offset dished pistons and rebuilt bottom end, wade 140 cam, twin side draught webbers, double valve springs. head will have 37IN and 33EX valves, all ported and matched.

changing pistons to flat top isn't an option, i didn't want to go down that path. im only left with shaving the head.

so should i be aiming for 9 or 9.5 with this setup? so i need to reduce the setup by about 3cc, is that alot to come of the head?

thanks

26cc is pretty small chambers (standard is 29-31 cc). The calculator says 9.1:1 on your combo?

Isn't it 372/43? That's 8.65

I just used the compression calc and yeah I got almost 9.5. So which should I go by?

9.5 is probably where you want to be at for Premium with dished pistons (flat tops could take 10:1)

Considering that stock 30cc chambers make 8.5 compression, I'd say go with the calculators. I used 0.6 mm as the gasket thickness and 79mm as the gasket diameter

Yeah same. Ok so I don't have to do anything. I thought that the head has been shaved. Looks like it has been. Thanks again DD. Always to the rescue

The calc is something like (372 + 43) / 43
uncompressed volume/compressed volume

(A15 is 1488cc, or 372cc per cylinder)

9.6 sounds perfect. Wade 140 is just a bit hotter (?) than GX, so it probably won't bleed off much static compression

Great. That's made me a lot happier.

dont forget singh grooves!

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