Dennis F,
Thanks for the reply!
I hear what you're saying about the milling the head of a flathead engine being a double-edged sword. I was guessing that the fuel/air FLOW wouldn't suffer THAT much (with a fairly stock rebuild) because the engine stays well below 4000rpms. Although I was considering that maybe a little relief grinding at the the piston side of the "valve pocket" to unshroud it wouldn't hurt - but again, with a 'operating limit' of <4K rpms, the valve unshrouding may not make much of an improvement. Of course, too much grinding will then increase combustion chamber volume and thus I'd loose whatever compression increase I'd of gained with a head shaving increase. I was merely thinking that a compression increase of 1 or 2 would be a noticable power increase. However, I don't know to what level of effect it would have with keeping it cool (since these are air-cooled engines) or with extra work for the OEM starter. Although I have read somewhere where you can rebuild your starter for more torque to handle higher CR engines.....
You mentioned that your machine shop, "...knurled the piston..."? I never heard of doing that. Knurling the valve guides, yes, but haven't heard of knurling pistons. Hmmm... why not, I guess.
What do you/anyone think about exhaust system changes versus benefits?
I'm thinking that a gutted muffler like what David Kirk did in his, "Killer Kohler Part II" article, would be a big gain for even a stock-ish engine for little cost. Nor would such a muffler put a strain on the engine; unlike higher compression, more heat generated, a thinner head, higher rpms, etc.
Ryan