Is there any difference in performance between the fuels on stock or near stock engines? Where I live/boat only have 10% other than driving miles and paying $4+/gal vs about $2.50 for 87 w/ethanol octane? Local on water gas advertises ethanol treated... whatever that means. I have 496HO. Local performance mod on 2 700sci and end result was 12+mph gain on a 42ft boat and it's tuned to run 87 and now runs 105+

thanks

If the octane rating is the same there are no advantages. Now if you are talking about E85 that's a different story. Biggest issue is Ethanol loves to suck water and can corrode parts not designed for Ethanol. I have a 1998 and I re-plumbed everything because I run 93 octane pump gas with 10% ethanol. I also use additives to keep it stable.

Theoretically you could tune a little leaner on pure gas for a little fuel economy gain.

The 10% ethanol mix will have a slight advantage of cooling the intake charge.

I built 9.8/1 540ci cigarette boat engines in 2006 when E10 first appeared in our area. Had the engines tuned while fully dressed on a dyno. Got them in the boat but had several small problems and ended up flying the guy who tuned it to come run the boat. We had to retard the timing 2 degrees to make them "happy". The tuner guy had never seen E10 at that time and thought I had bad gas.....turns out it's just the difference in E10 vs pure gas. I recall hearing somewhere later that E10 has 3.5% less energy that pure gas. I do know my cars fuel mileage dropped slightly when we made the change.

As for stock engines????? I doubt it makes as much difference as it did in that boat.

In hot weather, E10 will be more likely to give vapor lock problems than straight gas. The vapor point temperatures are about 20 degrees apart.

If your engines are circa pre-ethanol the performance gain by using non-ethanol in them will be not shredding the fuel system to pieces with ethanol alcohol content.