Oh,thanks 340_Dart, big differences between cc's. I have a custom pistons, but designed for 2.1"/1.625" valves and 63cc,->11.0:1 CR. It's hard decision...what a rookie mistake purchase pistons before heads, but i trust that chambers is what they have printed in catalog. 67-68cc after porting is not bad but everything above it, it's too much i think.
Every RPMs has been 63cc OOTB what i've been measured, thats very good "quality".