Dumb question... In my area the best gas you can get is 91 octane, and the nearest E85 station is about 200 miles away. I measured the ethanol content of the 91 octane at my local station (Costco) and it came about to about 8%.

Does the 91 octane rating include this small amount ethanol? Or is it perhaps slightly higher because of the ethanol content?

 

All pump gasoline these days is cut with a small amount of ethanol. You'll notice on every pump, it says, May contain up to 10% ethanol.

 

I believe it is the combination that achieves the 91 octane rating.

 

My very first tune was with 93 octane from Tom Thumb and my tuner was able to get 22* advance WOT. My second tune after headers was with 91 octane from valero and he was able to get 26* advance.

I thought it was strange and figured it was due to the headers, but also made me think tom thumb is a bunch of liars

I can tell the truck runs a lot better with the 91 valero vs 93 tom thumb and gets 1-2 mpgs better on highway.

 

It makes sense to me. If the only difference in Valero's gasoline and Tom Thumb's gasoline is that Tom Thumb puts a lot more alcohol in their's, it seems logical that your truck is peppier on gasoline that is less diluted. If alcohol had as much BTUs as gasoline, then it would be a different story.

 

I have always been told the cheapest gas will allow you to run the most timing because it usually has the most amount of ethanol. That being said, I can bring myself to put cheap gas in my truck. Not sure what my WOT timing is but I know that the initial value he used created some knock and he had to back it down a few degrees.

 

This is not always the case. The octane rating of a fuel is basically the controlability (that's not a real word, but you know what I mean) of pre-detonation. 87 octane is more prone to pre-detonate than 91 octane. E-85 is about the equivalent of 110 octane.

The cheaper fuels may have more ethanol in them, however they use the ethanol to boost the octane to that 87 or 89 level. Meaning the quality of the actual gasoline is actually pretty terrible, as they're having to augment it with ethanol.

 

Is E85 bad on the injectors/lines like ethanol is? gunky I guess would be the word for bad

Also my area has 5-6 gas stations that sell true unleaded gasoline no ethanol, but it runs $0.20-0.40 more. Should I be running ethanol free gas if available?

 

E85 is 85% ethanol so it has the same effects on fuel system components as any other ethanol based fuel and even more of an effect if your comparing it to the lower E10 or E15 fuels. That's why flex fuel vehicles have stainless steel fuel lines/rails and such.

Basically for mpg you want to run 100% gasoline. For performance you want to run the highest octane fuel regardless of if it is 100% gasoline, E10, E15, etc. If the ethanol blend fuels are mixed such that the ethanol is used to get to the rated octane then you will not get any more performance than running 100% gasoline at the same octane and will actually get better mpg from the 100% gasoline.

That being said, my tunner has experienced many different fuels in many different trucks and said that he has noticed, in general, that he can run more timing when using fuels from "cheaper" stations which generally means a higher ethanol content.