I have used the 241,820, and 292 casting heads. All are similar chamber shape ( xtra exhaust shrouding) and all that I have measured are as Pat has stated, 113cc. I have the 292 casting on a 30 over 402. I pocket ported them and added the larger 1.88 exhaust valves. (11/32 back cut/ stainless). They work real well with the current set up. Next week i am pulling them to add different springs as I am switching out the flat tappet cam in favor of Howards pn 12315-10 camshaft. (227/227/.555/.555 110). Its difficult to make compression out of these 402s. I am going to cut .015 off the heads and use the Mr. Gasket .019 head gasket. It should put me about 9.2 to 1 with the KB160 and i'm .020 in the hole. This compression should be fine for this cam. Good luck with your build...