Promaxx cylinder head question

[glockr]

Having a hard time understanding why they offer both 63cc and 65cc chamber versions of their head. If the difference was bigger I could understand, but only 2cc difference - that could be easily taking care of by head gasket thickness (like go from .030 to .040 or vice-versa). Are the chamber shapes significantly different, one for one type of application and the other for a different type of application? Are they all the same, but they sort by finished size and the ones that end up smaller get sold as 63cc and the larger ones sold as 65cc?

 

[rumblefish360]

The 65cc chamber is to clear the OEM 340 pistons that come .017 (IIRC) above the deck surface.

 

[67autocross]

I ordered a set a while back…they only had the 63s so that made the choice for me