Carl, it's a lot of guesswork unless some pretty sophisticated higher math gets involved, and that's a job for my aerospace engineer brother- - - - -way above my pay grade! Not much, if any cylinder pressure is going to be developed until the intake valve closes, so if a radical-grind cam keeps the valve open partway up the compression stroke, simple logic demands that the remaining cylinder volume needs a tighter squeeze to get the pressure back up to where it used to be when the valves were operating normally. As speed increases, the velocity of the incoming fuel charge keeps exhaust gas from entering the intake manifold when the valve opens before the end of the exhaust stroke. That's why over-cammed engines idle rough, or not at all at low speeds. I remember one 355 cubic inch round track engine we built with a roller cam, a rev kit, and altered rocker arm geometry that simply quit running below 2200 RPM, and didn't run smooth below 3,000. From 3,000 to 7,500, it produced awesome power- - - -enough to get wheelspin off the turns of a 5/8 mile high banked asphalt track if we chose the wrong rear end ratio. As speed increases, the efficiency gets better, so just figuring straight volumes gets into too many variables to be even close to exact.

Bottom line- - - -nothing much beats a few decades of engine building experience to get it right, and taking advantage of the technical assistance provided by the cam grinders, carburetor, intake and exhaust manifold manufacturers can provide definitely helps. Just beware of somebody who promises to solve all your problems with some expensive product that they just happen to have on sale!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!