I had a call from a friend that works at a local Mobil distributor. He had heard of my boat and wanted me to know he could fill one of my bulk tanks with 91 that has zero ethanol. I told him the engine builder suggested 93 only. He tells me 91 without ethanol is basically the same as 93 with ethanol. Any thoughts? Would you run 91 without ethanol over 93 with in an engine that's supposed to have 93?

Thank you.

Neil

No! The ethanol in the 93 would have lifted the octane of the original 91 (at least that's how I understand it). So regardless of whether its got ethanol or not in it, the lower the octane the more susceptible to detonation you are. If your builder said run 93 minimum, run 93!

If your getting a good discount, get some toluene & dump in it to raise the octane

Octane is octane. Run 93.

the lower the octane the more susceptible to detonation you are

True...however if you can get the no ethanol at a decent price, get it and add an appropriate amount of octane boost to it. You will get better performance and fuel economy due to the fact that you get more thermal energy yield from the "real" gasoline than you will from the 90/10 blend.

Get the straight 93. Octane can be raised with toluene, however educate yourself on the difference between points and numbers. If you go with mixing make sure you get the right formulas.

This is question directed towards ethanol in the fuel. I understand what is behind octane and why we need to run 93 in some builds but what I am not really clear about is what affect does Ethanol have on the tune. If the engine was tuned with 93 containing ethanol and if non ethanol based 93 was used afterwards what if anything would be of a concern?

It will run a tad bit richer, burn rate of alcohol/ethanol is almost twice that of gasoline.

Agreed, Ethanol is one of the large contributing factors to the soot build up I get on my Velocity 260 w/496 mag. These motors, by nature, run a bit rich. Add to it the inefficent burn of ethanol and it leaves me with a transom that looks like it has been coated with roofing tar. I have ben running 90 Octane no Ethanol gas this summer and have much less soot. I tried pump gas again last week, and the black heavy soot was back... This probably doesn't contribute to this discussion much..........