Thread: what do you guy think the highest compresson i can run on pump gas

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As Blackroc alluded to, you can run another full point of static compression ratio with aluminum heads over cast iron heads.

The limit on scr will be determined by cylinder pressure (intake closing point on the cam), head material, combustion chamber and piston crown shape and size, total ignition timing and advance curve, spark plug heat range and indexing of the ground strap, thermostat opening point, inlet air temperature, air/fuel ratio, your elevation above sea level (air density), squish (distance from the piston crown to the underside of the cylinder head with the piston at TDC), rear gear (lugging the motor with a tall gear will allow detonation to occur easier than a short gear), whether or not there are any hot spots in the chamber/cylinder and whether or not you're polluting the incoming charge with an EGR or PCV system.

With everything optimized, it's possible to operate at a little over 11:1 with iron heads on premium pump gas with no octane booster.