Yah - propane is up around 112-115 (R+M)/2 octane, or thereabouts. It's also a nearly pure hydrocarbon - the only additive is beeswax, and that's why it burns so cleanly.
"Static Compression Ratio" - the ratio between the volume above the piston when the piston is at TDC, vice the piston at BDC. Determined by engine component selection, as above - and without respect for camshaft selection.
"Dynamic Compression Ratio" - the ratio between the volume above the piston when the piston is at TDC, vice the piston
at the moment the intake valve is closed (which is usually sometime after the piston is travelling upwards.) This is always lower than the SCR, and can be changed by installing a different camshaft (even when all other engine components are the same.) I don't have the formula to hand, but it's readily available, and there are a couple of Javascript calculators online as well for the maths-impaired (there are a few of us out there.)
"Quench" - the distance between the deckline of the piston (flat surface) and the deckline of the cylinder head (flat surface.) "Ideal quench" is usually taken to be .040-.060", and this "squish band" forces the fuel/air mixture to be turned inside out in the combustion chamber as the piston reaches TDC. This inversion reduces the overall combustion chamber temperature, which reduces the potential for detonation due to compression ("spark knock" or "preignition.")
"Octane" - this can be taken as several numbers - "Motor Octane Number" (MON,) "Research Octane Number" (RON,) or "Pump Octane" (typically what is referred to, calculated as (R+M)/2.) A higher octane indicates a higher resistance to ignition, which means that the fuel/air mixture can be compressed further (gasses will heat up as they are compressed) before it will spontaneously ignite. This is what I'm trying to sort out - various minima for octane numbers (irrespective of other factors) with various DCRs. Factors that can affect octane requirements:
- Cylinder Head Material
- Engine Block Material
- Engine Cooling System Efficiency
- Engine Coolant Composition
- Heat Rejection of Radiator
- Direct Cooling of Combustion Chamber Components
- Combustion Chamber Quench Distance
For instance, oil jets can be directed at the bottom of the pistons to cool them (a common turbo-builder's trick,) which can allow the use of lower octane fuels.
There are a huge number of factors involved, but what I'm trying to do is generate a "jumping-off point" for stroker builders. An educated guess is better than a wild-assed guess anyday...