compression = horsepower query

Thanks Rumble, one of my problems is that i dont know the exact comp ratio. I used Sealed Power pistons (H405cp), which as i understand it, provide more compm than the original pistons, but not a whole lot more. Beyond that, the heads were lightly skimmed and the cc is 68 as I recall. Head gasket (compressed) .027.
Here in the UK heads are limited in their availability, which in turn limits my options