Not that $ is the only issue but I can only get 93 at the Marina which is $1.25 more per gallon than 91 I get on land next to the station where I store my boat. So at 300 Gallons per month thats $375 per month difference not $30. I really appreciate all of the input but must admit that I am even more confused now. Both sides make very good cases and back them up with real life experiences and math. I guess bcfountain said it best. Detonation is a mother! Although I really think the 91 would be fine (hell that's all you can get in some states) I'm not gonna risk it. I didn't buy a 75mph boat to take go easy on it. I'll burn the good stuff! Thanks again all!

I put some 104 with my 93 when I know I'm going to run it hard,kinda insurance.

On my Scarab I would get in the engine compartment get a guy to drive it in gear.I would work the throttle at the carbs,get someone to hold the hatch,whale on it see if it pings,yea its a crude way,

Do they still make a lead substitute?


Also had a buddy that had a spapific gravity checker, we would go arong to the gas station see wich one had the best #'s 715-725.The race fuel he was making was 705.
Rob

Add 1 gallon of Toluene or 114+ race fuel for every 24 gallons of 91 octane. That will put you at 92 octane.

That or run about a 50/50 mix of the 91 land fuel and 93 on water fuel.

Old tread. But I did use the search function. What is worse using 93 with ethanol in the 525sc or use non-ethanol 91?