Which gas? 91 (ethanol free) or 93 w/10%
 

I have the ability to buy ethanol free 91 octane gas at the pump. And also can get 93 octane w/ 10% ethanol.

What would you run?

I don't care at all about gas mileage (as only track the car and trailer it to events)

The ONLY thing I care about is taking car of the engine.

I do have a Pettit Built 13B Race Spec engine but no special tune.

I'm not going to spend the $$$ for higher octane ehthanol free race fuel.

It doesn't matter which you use.

Interesting question, I also have access to 91 ethanol free. I've not used it yet but would be interested if it would make a difference. Maybe if your car sits for long periods of time, you would not have to worry about the ethanol absorbing water.

You'll have less power and mpg on the 93 oct because of the ethanol.

Out in West Texas and other high plains areas 91 is the highest and still has ethanol.

At sea level is only where 93 oct would be maybe needed.

While you can use either my preference would be the 93 with ethanol . You don't need the higher octane but ethanol does have some properties that make it desirable in a rotary engine .

Ethanol has something like 30% less energy than gasoline. Therefore, 10% ethanol gasoline will have roughly 3% less energy than pure gas. It's not really enough to worry about.

I know what you mean; on paper it looks like nothing, but my butt dyno seems to not like it.

I was fuel distributor, so I should know these things. (Still not saying expert)

Actually, I'm confusing the winter gas mix where they actually put more butane molecules in for vaporization.

The refiners used to put more butane in summer, too, but the EPA stopped that.

Summer gas really is better, and the OP should just run which he likes or mix and match.