The compression in my 388 right now is 9.9:1 with 60 cc aluminum heads. I'm planning on putting a supercharger on and at the same time want to get better heads like the AFR 195's. I'm hoping to kill two birds here because the AFR's come with 68 or 74 cc domes. What do you think the compression would be at with the 68cc heads and what would it be at with the 74cc heads? I'm hoping to get right around 9.0:1.

 

Greg,

There is a lot more than the head volume in the calculations for static compression ratio. Check this file: Engine Calculations.xls Just download the spreadsheet and enter your data, It should get you close. It doesn't take into considertaion the head gasket volume from a diameter perspective, but I'm working on that one. If you are using head gaskets with no extra bore clearance, it will be right on the money.

 

Greg- I can calculate anything from anything if you are ABSOLUTELY CERTAIN that your beginning compression ratio is really 9.9:1.

IF it is really 9.9:1 to begin with AND your reads really are 60cc AND you resuse the same type head gaskets you have now then switching to different sized combustion chambers will yield the following compression:

64cc = 9.54:1

72cc = 8.86:1

74cc = 8.71:1

 

....and a 68cc would give you 9.1:1

 

That's exactly what I needed thanks a million!