Technical explanation, please....

[JNM240]

I was just wondering if anyone knew exactly why putting SOHC pistons into a DOHC motor raises your compression so high? My 90 8.6:1 pistons have a slight dish to them, and i believe the 89 9.1:1 pistons are flat top. The dimensions on the SOHC and DOHC blocks should be identical, right? But if you drop 8.6:1 SOHC pistons into a DOHC block, you get 11.1:1 compression ratio, right? So is it the size and/or shape of the cylinder head combustion chamber? I believe my 90 SOHC cylinder head combustion chamber volume is 60cc's. If anyone has a technical answer, i would love to hear it.

[Rev_D21]

It's both size and shape that equal volume. Volume when the piston is at TDC is what you are looking at.

[TrunkMonkey]

I was just wondering if anyone knew exactly why putting SOHC pistons into a DOHC motor raises your compression so high?

class is in session...

the DOHC's cylinder head has a smaller combustion chamber than the SOHC. the DOHC's pistons have a deeper dish than the SOHC.

the SOHC's compression is raised with flattop pistons (eliminating the dish). the DOHC's pistons are deep enough so that using another piston with a smaller dish (the SOHC's) increases it's compression.

i hope this helps.

-demetrius