Jim V is going to be porting my combustion chambers to help reduce the compression on my Promaxx heads in preparation for boost. They start at 119cc, does anyone have any experience on how many cc’s can be removed on a head like this?

When I was done cleaning up the Edelbrock chambers it removed 10cc by the time I was done and good for .68 of a compression point.

Jason, I spoke with Jim on Saturday regarding my project. I am sitting around 9.8 right now and would like to get down in the 8.5-8.75 range. I understand this will not be doable with the porting alone but am hoping he can remove as much as possible while helping flow. I will still have to run thicker head gaskets but I am trying to run the thinnest gasket possible after the porting to get me to my desired compression ratio. Jim was thinking he could get them into the upper 120’s while increasing flow. I would be very happy with 10cc’s but a little more would be even better!!

Whats your current bore stroke and head gasket?

4.560 bore, 4.375 stroke, .027 gasket, piston is about .025 in the hole.

Does the quench become an issue at some point?

Research has shown that in blown applications quench can be basically disregarded. Merc 1075 has a .051 head gasket with the piston being .098 in the hole. It uses a flattop piston as well.

Piston cc?

flat top with 3cc valve pocket.