Highest compression on pump gas?

Crower made a camshaft for smallblock chevies years ago that had a very late-closing intake valve. It was specifically designed for higher compression ratios and pump gas. IIRC the only test had indifferent conclusions, and I believe it was from higher-than-normal reversion pulses causing the carb to go rich. It'd probably go better with fuel injection. As late as 10 years ago Crower was still trying to get rid of them, I saw them on the 'bay.

R.

The Prius engine runs at 13:1 compression on regular gas using this principle. Also Mazda's SkyActiv gasoline engine uses something similar.

So...what about all the Pump Gas Drag guys that claim to run pump gas with 12.5 compression? Are they running cams with alot of duration?Probably adjusting their timing back and forth all the time?

Ya, one place in town has got 94, everyone else is 91.

Back to Mazda. The major thing they did to allow that high compression ratio, up to 14:1 in Europe on premium pump gas, was to decrease the temperature of the incoming air charge.
They do this two ways: first, some fuel is injected on the intake stroke, evaporation cools the incoming air, then more fuel is injected during the compression stroke.
Second, the exhaust gas residual in the chamber was found to have a major heating effect on the intake charge, so they cut it in half by using a 4-2-1 header. There is also some business about the piston top, which features a nice hole right in the center. I did not understand the explanation they gave, something about not heating the top of the piston.

It's fascinating to see developments like this.

R.