calculating compression ratio

**Ryder** · 03-07-2009, 01:41 PM

Ahh i see it now.

That is a bit odd...

**GD Engineering (Gavin)** · 03-07-2009, 08:38 PM

Hi mate. Again, you don't need to know anything about the crown of the piston to work out CR. The crown can have 500 million humps/hollows/angles ang a gorilla's arse cast in it........ still doesn't matter if you do it empirically.Try and keep the gasket under 2mm if possible as heat yield will kill it ( thermoplastic deformation ) and also be sure there is enough free camchain to allow such a height change. One of the drawbacks of closed deck motors such as these is that you are stuck with a choice or combination of lowering piston compression height or headgasket thickness change. Older open deck motors allow this to be done at the bottom of the barrel, thus allowing the use of a thinner head gasket, a better way to go for reliability. Expect to run 7-10 psi on 98 RON without charge air cooling or a comp reduction due to the relatively favourable combustion chamber topography. Reducing it to 9.5-11:1 should see you being able to run 8-12 psi depending on a number of factors I won't go into. Hope this helps and good luck.

**Ryder** · 04-07-2009, 08:53 AM

Thanks very much for that mate. This project should be quite a learning curve!

I'll be starting a thread in members projects for this next week sometime...

**Ryder** · 04-07-2009, 03:02 PM

I found a great link for how to accurately measure swept and unswept volumes, will post it here as a reference for anyone else who may need it in the future.

http://www.scca.com/documents/Club%2...FCompRatio.pdf