You are correct that most "octane boosters" raise in points not full octane numbers.

The fuel engineer I spoke with that supply's the fuel specifically spoke 92. Now he could be wrong. I myself have never believed in "off the shelf" additives. But this is an addative that is mainly sold in quantity to fuel companies not consumers....might be better?

I was and still am skeptical but plan on taking the straight 90 to the dyno with me along with the 90 treated with valvetect to see for myself. So far on the water we are having good luck. Is it due to all our engines not actually requiring 93, that the manufactures just require more so they have a saftey margine? Or are we just lucky? Or that Tue valvetect increases octane?

I agree with MT though. If the fuel is fresh 93 is great. If the fuel will sit the 90 non ethonal might just be a better option. That's the main reason my friends and I started running the 90.

Don't confuse this with all ethonal fuel is bad. I've seen test that show no issues. But we don't know what's in the stations tank, how long its been there, rate of turnover, or when the weather will clear for another boat ride!

The way it's been explained to me by our fuel supplier at our marina, octane rating is a minimum requirement. Ethanol or not it should be 1-2 numbers over the sticker on the pump. He said ethanol is going to change the rating but they'll sell it as the higher octane fuel.
With that being said, I have 600sc clones turned up to 11psi and I run 93 ethanol or 91 ethanol if I can't get 93 and never had any trouble.

I think 90 is going to be worse than 92 with or without, you need to keep the octane to stay out of trouble..like mild said mercs are rich to begin with so the ethanol not a bad thing for the cooling...we race on E85 and love the stuff...still get mixed info on AFR running the E85 though..

Just my limited knowledge to help you guys out maybe....I used to work at an ethanol facility in the northeast owned by a major fuel provider. Cough cough they supply all the ethanol for those cars you see on tv every Sunday and the like from our facility. They make100's of thousands of gallons of pure ethanol every 12 hrs(200 proof moonshine, no you wouldn't want to drink it, it was hard enough being in the same room as an open bottle). It's all tightly lab controlled in order to ship. The moisture tolerance before shipping is very small, I'm sorry I dont remember the exact number. I want to say less than 1%. They're also required to denature the ethanol as stated earlier. Where I was it was with a small amount of 87 regular gas so that the ATF couldn't tax it as alcohol. It is true that the ethanol is an octane enhancer. If pure around 120, so what you get at the pump is actually higher than the rating they're showing. Like I said earlier the moisture tolerance before shipping is so minimal with the quantities produced I now have no problem with ethanol after working there. That's about all I have besides the fact that my parents cruiser (twin volvos) sits at a marina in the water all season with minimal run time and never has a problem with start up or hard running. They'll typically get 2 seasons out of a tank these days with only stabilizer added going into winter.

Yep, too cold to atomize properly in colder weather. That's why in MN, their E85 is actually E70 in the winter.

Does anyone run a stock 600's with 87 octane??