Compression ratio
Posted: Tue Mar 13, 2018 9:04 am
Hi, I need your expertise to figure out correct cylinder head skimming.
I have raised the top of my exhaust port from 40mm to 33mm. Since compression ratio is calculated from top of exhaust port, I need to skim the head to maintain same compression rate or even increase it.
I measured the volume of what I believe to be a stock M/A/B cylinder head at 30cc. My calculations give a compression ratio of ca. 5,3 for a stock M/A/B cylinder with 40mm exhaust port. I assumed a deck height of 0,6mm and a head gasket of 1mm thickness.
How much would I need to skim the original cylinder head to keep the same compression ratio of 5,3 with a reduced exhaust port upper edge of 33mm?
In my calculations I would need to reduce the combustion chamber volume from 30cc to 22,5cc, which means skimming off close to 2mm from the head.
Is my assumption correct? Can someone confirm the volume of an original cylinder head?
I have raised the top of my exhaust port from 40mm to 33mm. Since compression ratio is calculated from top of exhaust port, I need to skim the head to maintain same compression rate or even increase it.
I measured the volume of what I believe to be a stock M/A/B cylinder head at 30cc. My calculations give a compression ratio of ca. 5,3 for a stock M/A/B cylinder with 40mm exhaust port. I assumed a deck height of 0,6mm and a head gasket of 1mm thickness.
How much would I need to skim the original cylinder head to keep the same compression ratio of 5,3 with a reduced exhaust port upper edge of 33mm?
In my calculations I would need to reduce the combustion chamber volume from 30cc to 22,5cc, which means skimming off close to 2mm from the head.
Is my assumption correct? Can someone confirm the volume of an original cylinder head?