Originally Posted by 60wag
What's odd though is that from 4% EtOH on up to 20%, the vapor pressure doesn't change much. So the change from 10% to 15% shouldn't make much difference other than the loss of energy density (lower mpg).
Do you have a chart somewhere you could turn us on to? I would expect a linear change in vapor pressure as the EtOH concentration is increased. It's a pretty darn light little molecule compared to Heptane. FWIW, I run premium in my 60 since I had the head decked.
One other interesting tidbit. 60s recirculate the return back to the pump, so it all stays in the engine bay where it's hot. My 76 recirculates back to the tank where it should be a lot cooler.