Compression ratios and piston choices
Turbo Mini Forums

Hi Guys,

Im just looking at putting together my build spec and looking for a little help and advice.

I have already got a cylinder head; a MED unit with a 28.5cc compression chamber.

Going to get +20's for a 1293 and using an online calculator (and using values I have got from TM for the headgasket volume) im stuck as to what pistons to get to give me a usable compression ratio.
Assuming around 1cc for ring land.
But otherwise as far as I can see, for around 8.06:1 I would need 13cc dishes.


Looking at the Omega forged line, they do an 18cc piston and a 6cc piston.

Am I better using the 6cc piston and either running it down the bore and/or machining bigger dishes into them?
or using the 18cc pistons, getting them machined down to a suitable CC? Concern being that taking that much material off could make the ring lands weaker?

Cheers,

Dave.

David.

The cast 10cc Omegas on an undecked block sit around 0.040" down the bore, so will give you 14cc total.
Do you need a compression ratio that low ? If not, you could take a little of the block to bring them higher, which is better.

Phil.

WWW.TURBO-MINI.COM

The cast 10cc Omegas on an undecked block sit around 0.040" down the bore, so will give you 14cc total.
Do you need a compression ratio that low ? If not, you could take a little of the block to bring them higher, which is better.

Phil.

WWW.TURBO-MINI.COM

Planning on using GT20 turbo so quite moderate boost achievable, going on recomendation of a bit lower compression is more suited to moderate to higher boost? desined for track oriented car.

I had seen the 10cc Cast items but was looking at the forged line really for bit better reliability and durability.

David.

as phil says, .................. as well IMO and experience and in SHORT! building many engines, if your using hi octain pump fuel just deck the block 0.020" and use those 10cc omegas + 20s job done, use an efficient intercooler as well