Originally posted by techinspector1
I've witnessed example after example of iron head street motors running at up to 11:1 on pump gas with tight (0.035"- 0.040") quench and cams with delayed intake closing points.
Quench, we used to refer to it, in the old days, as mechanical octane. Its main purpose is to provide a more homogeneous mixture around the plug. A homogenous mix will burn more consistent and" smoother" therefore lessening the chance of spark knock.

Later intake closing is crucial in controlling detonation in an engine like you describe. The later intake closing reduces cylinder pressure and in effect makes the engine " think" it has a lower compression ratio. Conversely, an engine with a lower compression ratio, say 9-1, can use a tight quench area and a cam with earlier intake closing events and generate the same cylinder pressures as the 11-1 engine in your example. This latter combination works well in low RPM street engines.

Aluminum heads reject enough heat, which also reduces cylinder pressure, to allow an increase in static compression ratio (usually .5 to 1 point), which restores the lost cylinder pressure due to the aluminum material.

I agree that the tighter the quench the better it seems to work. In our race stuff we usually stumble on to the point where the piston just touches the head and then back off a couple of thousandths.