I believe you are correct; the Twin Cooled HO103 is the only 103 with 10:1 compression; I stand corrected. The addition of liquid cooling allowed the increase in compression and cam timing change which translated to in increase in power but I don't know how the compression increase was developed.

 

i have learned just in the last hour to achieve the higher compression the combustion chamber is pear shaped on one end and is like 83 cc’s and the compression is closer to i think 9.9:1. Thanks for the replies !

 

Are you sure about that? I would like to see the side by side photos of the 9.7:1 and 10.0:. Not doubting what you say but adding to the production cost of a cylinder head to gain a .3 increase in compression is inconsistent with the HD approach to cost and production. The early SE Performance heads were milled .050" with no change to the chamber shape.

 

well the heads were already diffrent because of water cooled i may be able to show both pics

 

 

the first pic is a standard 103 ho air cooled the 2nd pic is the 103 ho twin cooled see the pear shape in the combustion chamber its tapered on the end

 

Thanks for the pics.. I've wonder how they did it..

 

Thanks for the photos. I didn't think about the possibility that the liquid cooling was driving the chamber configuration but that makes total sense. No way would the MoCo change the chamber configuration for reducing chamber volume by 2cc but the liquid cooling forced the change.

 

your very welcome im wondering if with the cooler running heads how much ccp one could get away with on 93 octane or if any more than the air cooled ive got thoughts about trying it with my 57 h cams and a 0.30 head gasket ? Just a thought! Any opinions or info very appreciated!

 

If you are talking "wet head" at 10:1 but replacing the OEM head gasket with a .030" head gasket with a set of Andrews 57 cams CCP will be about 200psi and corrected compression about 9.6. That is about as far as I would go with that cam but others may disagree.