Static "compression" and actual CYLINDER PRESSURES are two different animals and now you can toss in DYNAMIC CYLINDER PRESSURE -- and it's the later that will make a difference in what fuel you can run and your timing. Timing is the killer if you're on the verge. The right timing curve will get you more power than will one or two points of octane.
Dynamic cylinder pressure is the calculation of the ACTUAL swept area of the cylinder. In other words -- where the INTAKE VALVE closes in relationship to the piston coming off BDC. You can loose an INCH off the stroke if the valve closes late compared to closing "earlier". HUGE difference in the calculation and DCR is ALWAYS lower than SCR.
Then factor in Cylinder pressure - which is constantly changing with RPMS etc. DCR can be calculated -- and CP can be measured. I'd be looking for CPs under 200 with a carb. Or a DCR of 8.25:1 or less but no less than 7.5:1 on 91 octane.
Modern EFI cars can pull timing out with the knock (detonation really) sensors... thus they can run on the ragged edge and be able to "bail out" (pulling timing out) when knocking is sensed. EFI can also "add" one point to the compression number -- as does the aluminum heads. That's why you see LS motors (etc) up there in the numbers game.
So --- There are aftermarket knock sensors. And you can get a dial back timing module (MSD) to use when you'd need it. You'd need the knock sensors because by the time you might notice the problem - you may already have a problem! But I agree with everyone else here... WHY would you purposely build a grenade. Keep the cylinder pressures down in safe zone and drive and enjoy the car all day every day. Nothing is worse than a poor running, overheating POS. And we've all had those! They suck.
My advice --- and you can do this easily before you ever fire off the motor -- is to check the numbers calculating the DYNAMIC COMPRESSION... or at the very least - do a cylinder pressure check and compare those numbers with known 'limits'. Because it's the combo of the cam and head chamber size - gasket thickness - and static CR number of the pistons - and where they TDC in the bore (quench area) as installed etc. that will determine what you really need to know.
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