seat of the pants and also my friend has this "G TECH" dohicky that is also very accurate...we have used it on dyno'd cars and it and awesome tuning tool.

the old cam was stock, along with the heads and intake etc. i have a 4 speed in a 1960 chevy truck (3700 lbs w/me in it and a full tank of gas) 3.73 rear gears. 28 in tall tire. it pulls fine until about 3500ish rpm. i dyno'd the truck and it made a whopping 206 whp @ 5200rpm up here at 4500 ft. which equates to about 230hp at sea level. it power just levels off for the most part after 3500. but i'm shifting at around 5500 where i should be. right now i'm using shell regular 89 octane for gas.

and in my compression i did not forget the deck height or the piston dish.
stock piston dish is 20cc for my 74 truck 350. it is also bored .060 over.
stock deck height is .025
gasket is .015 inch compressed....etc.
and with all that info put into the compression ratio equation, comes out to exactly 9.17:1

and the cam has 5 degrees of advance built into the lobes. isn't 9 degrees of cam advance a little excessive???? and i honestly don't think that i need that much compression for this cam, yeah a little more because of the elevation, but even edelbrocks performer rpm crate engine only has 9.5 to 1 compression and that cam is quite a bit bigger than mine.

also my friend has the performer rpm cam in his pontiac 428 with just under 9:1 compression and he is even getting a minimum of 120 psi cranking. that cam has 4 degrees of advance built in it.
so theoretically my cam installed exactly how it is in the truck (retarded 2 degrees) is only retarded 1 degree more than his with about the same compression ratio and he has a lot more duration/overlap than mine too. AND he has .5* less LSA!