al, as you have correctly assumed, the cam has a lot to do with it. More specifically, the intake closing point of the cam lobe because that is what determines how much of the charge will be trapped for compression. You might build an 11 to 1 motor and use a very long cam with a lot of duration (and therefore a late closing point) and build maybe 160 psi (I'm just pcking numbers here to make a point). You might also build a 9 to 1 motor with a very short duration cam (and therefore an early closing point) and also build maybe 160 psi.

The overlap doesn't come into play here except that with a very long duration cam, you will be increasing overlap because you have to open the intake earlier and close the exhaust later to get the higher duration numbers, but overlap doesn't determine cylinder pressure. It determines lope, because the earlier you open the intake, the more chance there is to push burned exhaust gases back up the inlet tract and disrupt the air flow signal at the venturis of the carb at lower rpm's as the piston evacuates the cylinder.

The intake closing point can be changed in the motor by advancing or retarding the cam in relation to the crank. Advancing it will open and close the intake earlier to capture more mixture, building more low-end torque. Retarding the cam will open and close the intake later and result in more high-end torque.

Although I haven't experimented much with retarding the cam, I suppose you could retard it a few degrees, closing the intake later and bleed off some cylinder pressure to lessen the tendency of the motor to detonate. dr_bowtie has played with this more than I have, maybe he'll see this and offer his experiences with retard. If not, e-mail him and ask. I've been pretty lucky I guess, with setting the compression ratio, squish and cam selection to preclude any detonation problems, so my advance/retard experiments have been to gain a little more on the bottom end, not to eliminate detonation.

You can get a pretty good idea of the intake closing and how it relates to c.r. by studying the Crane Cams site and comparing different grinds for a SBC. Look at the 0.050" closing points and the recommended c.r. range of the cam. After you look at enough of them, you'll begin to get an idea of where the intake needs to close to accomodate a certain c.r. Of course there are other areas of cam selection to consider, operating range being perhaps the second most important to me, then whether or not it will work with a stock converter if I'm building a very mild street motor.

The bottom line is that the cam should be the last item you choose in your buildup, after you have installed gears, converter, intake, exhaust and the other engine parts it will take to do the job.

Everybody starts at the wrong end of the car.