I run 100LL Avgas in my 12:1 427. It works great, or as good as race gas and I pay a lot less at my flying club for it. I run premium pump gas in my 9.5:1 HiPo 289, also with great success. I give it a shot of 100LL every once in awhile to put some lead on the valve faces. As for using 100% race gas or Avgas in a 9.5:1 engine, it's a waste of money. Besides the slower burn of either doesn't do your exhaust valves any good. And backing off spark lead to be able to run low-octance gas is giving up potential power. As for O2 sensors, I don't need no stinking O2 sensor.
