compression reading=what ratio???

[300exPA]

I have a 330 with a decked head. I want to make sure that I am running the correct octane. If I put a compression tester on my quad, how does the PSI coorespond to the compression ratio?:confused:

[oynot400]

I don't think that will tell you, not completely sure though. I had the same question a while back to see what my compression ratio was. I asked my engine builder, he said to put the piston on TDC and fill it with fuild with a syrenge (sp?) to measure the amount. Then there is a formual that will figure it out for you.
If there is an easier way I would like to know.