I was told by Mike Danniballe at Sterling that the only way to boost octane of pump gas is to add high octane race gas. Advertised "octane boosters" absolutely do not boost octane of any levels of fuel. If you need 93 octane for your motors, but can only get 87 octane at the pumps, you will need to cut the fuel 1/3 with 110 octane race gas to end up at 93 octane. I only need 91 octane for the Merc 700s in my 36, so when I know I can only get 87 octane, I need to cut my fuel 20% with 110 race gas to end up at 91 octane. The octane level of race gas you buy depends on the percentage you need to cut the fuel by. It's simple math, and leaded race gas is always recommended over low-lead 100 octane av-gas.

I went the 110 route a few times but that can be a real challenge if your traveling on the water. I have even stationed cans where I'm going but that is a real pain in the as .

More food for thought...Thanks!

Down here that is one reason I do not want anything that needs more then 90, its what you find on the water and a lot of times we go through more then a tank in a day. At least with a boosted injected motor you could have it pull timing or try to stay out of boost but what fun is that?

Boostane is by far the best

I have tried Octane Boosters, But the Best was To buy TRICK FUEL is 110% ( 10 % ) in the tank with you 87% Octane Worked Great, In My 28' Bertram Baron Special.
350 Mag. Eng, squared out 350 hp.each.

I run a Donzi Blackhawk with a supercharged 502 with good heads and bottom end it's carbureted and running Boostane allowed me to advance my timing when I went to more pitch. It seems to do a good job.

Good idea! I am reviewing this as an option. Ideally, I am looking for a "concentrate" that I can carry in the boat to add to 100-150 gallons of 87 (from a marina) during refueling in order to get ~92 octane.
My basic math calculation says that I would have to carry/add ~28 gallons of 110 to 100 gallons of 87 to get 128 gallons of 92.

Do you have knock sensors or was this "by the ear"?

I would not risk blowing an expensive engine using octane boosters. Hard to believe less than an ounce of something can raise the octane of one gal of gas. This has been debated for years on many forums and the general consensus is octane boosters are not what they claim.