I always run premium. She runs best on 100LL from the airport.

I run regular unleaded on stock 95' 5.0. With Demon carb

RV6 wrote:

I always run premium. She runs best on 100LL from the airport.

 
Do you notice that your gas mileage is lower? Or is it just me?

87 octane Reg. gas here. 

87 octane ethanol free for me.Runs great. 

I run 89 octane.  Probably could easily run 87.  The mileage will always be best with the lowest octane fuel the engine will tolerate.  No way to get ethanol free here unfortunately.  Every station in the state has it.  Damn corn lobby.

In Canada 93 octane is corn free and unlike lower grades equates to better mpg.

Toploader wrote:

TKOPerformance wrote:

The mileage will always be best with the lowest octane fuel the engine will tolerate.

Really?? The Gas Companies promote the higher the octane, the better the mpg. I'm interested to learn more on this.

Yeah, they really throw a fine line of BS at you about a lot of stuff.  The problem with higher octane fuels is that they are harder to ignite, and burn slower, particularly in an engine with lower compression than would require that octane.  You get the most complete burn running the lowest octane fuel the engine will tolerate.  I tested this with a Kia my wife had years ago.  She kept putting midgrade in it and I told her to stop.  A couple weeks later she commented that the fuel mileage was up about 20 miles per tank running 87 instead of 89.  She's a creature of habit too, so her weekly driving routine, especially at that time (pre kids), was absurdly consistent.  It equated to something like another 1.25 miles per gallon. 

We used to run 110 Low Lead in mu uncle's '67 L88 Vette.  Yep, aviation fuel.  One of the perks of having a hanger at the local airport at the time, back when no one asked any questions.  Still the scariest car I've ever been in.  It didn't have an accelerator; it had a tire spin pedal, and located under it and close to the floor there was a spin the car 180 switch.  On drag slicks it went mid 10s at the Vette Nationals at Carlisle with our good friend (and the guy who built the car) Bobby Gold driving.  That's still stupid fast, but it was insanely stupid fast for the late '80s.