[chiphead]

I run E10 93 in my '67. 69 400 with 62 heads and 2802 cam. I would run 93 straight gas if I could find it, but all I can find is 89 octane. 91 straight gas would be fine. Lead additive supposedly helps more with valve seat erosion, but not sure the modern formulations really do anything. I would not add any light oil (marvel mystery, etc) to gasoline. OIl reduces octane and can aggravate detonation.

The most obvious issue I have is gas vaporizing in the holley carb at idle. E10 seems to vaporize more aggressively. The AFR goes into the 11s at idle with air cleaner on, its 13s with air cleaner removed. Only does this when hot, so I assume it's carb vent fuel vapor being pulled back into the engine.. The E10 gas also evaporates really quickly if the car sits. Also, the E10 doesn't color the plugs like straight gas. I've run AFRs into the low 10s and the plugs stay pretty clean. E10 runs about 5 percent leaner than straight gas, so you need to go up 1 jet size when running E10, assuming the engine is tuned properly for straight gas. No audible detonation, no black specks on plugs and no overheating.