My A14 reads 220 PSI (1520 KPa) on a compression guage. Does anyone know how to convert that to a compression ratio?

I have a theoretical way. I'll dig it up tonight and post it tommorow. But I've never had any success with it. I'm thinking that the three compression gauges I've tried haven't been able to accurately measure the pressure. Maybe the old dial type gauges aren't able to react quick enough to get a proper max-pressure reading.

But, comparing it to my engines, it sounds high! Maybe even too high for standard fuel. The actual static compression ratio is completely dependant on the timing figures of yuor cam. Ie, the inlet valve closing figure.
Do you know your cam specs?

It's an exchange motor (HM Gem) that I know nothing about except in pings a lot. The dizzy's in good nick and the carby's brand new. I think the new head may have been planed back too far and would love to figure out the comp ratio.

Does it ping when cold or only after it started to warm up a bit?

The reason why I'm asking is I've also got a A14 motor with serious knock/ping problems. Im at the point of pulling off my cylinder head and scraping of any form of carbon. *expect a post later on, on how to remove and replace cylinder head*

It'll ping any old time it likes. I'm on top of the mixture and the timing but the only thing left is the possibility of high compression. If it turns out the comp is high (as I suspect) then I'll get hold of some octane booster and see if that helps.

Well factory specs are 185psi fresh.

185 PSI yeah, looks like I'm well on the high side at 220. Would like to figure out what that equals as a ratio.