I have no idea what they are someone with some insight please spread some light on the subject for me. I.e whats best for 2ltr zvh what they mean etc etc...

 

the compression ratio is the ratio difference of how much the air is compressed from when the piston is at bottom dead center to top dead center (piston at the top of its bore, piston at its bottom)

i cant advice on a actual compression ratio as it depends on so many things!

 

So the more you have the piston machined down the lower the compression ratio will be? what do teh numbers stand for then like 8:5:1???

 

volume ratio for when the piston is at bottom dead center(greatest volume) compared to when the piston is at the top (least volume)

 

If you machine the piston you will have MORE compression, think carefully and take advice from people who have done this as todays fuels are not that tolerant of high CR's.
On a car that is NOT forced induction you only have the ONE CR to worry about, obviously if it is Forced induction, you need to figure in the ADIABATIC CR as well, as you have TWO CR's.
tabetha

 

It means that the volume of the cylinder at BDC is 8.5 times greater than when it's at TDC.