[Formulajones]

Originally Posted by Navy Horn 16

Pump gas can be up to 10% Ethanol. That's all you know about your pump gas, other than the octane level. How much actual ethanol that is in your gas will vary from station to station and tank to tank. It depends on how much ethanol cost at the time they were blending, how much RINs cost, how much the blender was willing to pay for carbon offsets, and several other factors.

There are bean counters and chemists working at the refinery to make sure the right blend of gasoline and ethanol makes it to the premium and regular tanks.

It isn't something that you can tune your carb around. That's why I run a mix of 90 octane ethanol free and 100LL. Ethanol has less energy per unit of volume, so you can make more power by getting rid of it from your fuel system.

Actually you can know more than that. They have made small ethanol test kits for years. Cheap to buy and probably still all over ebay.
Back when I was testing that stuff, I found as much as 17% ethanol at pumps that were advertised at 10%. There was no real consistency that I found. You can tune and crutch it to some degree. In order for a car to run properly on it the circuits have to be modified. Mainly the idle circuits have to be richened, and it's a good idea to run the engine a little on the rich side of stoich to cover any inconsistencies.

But the real point of my post was to elaborate a little on what I felt Steve meant.