When we have a setup that is at it limits on pump fuel we add a splash of race gas and make a pull. If power goes up you know there is a potential problem with the tune-up. If it goes down then you are usually in the safe zone...

From my research and what makes me feel warm and fuzzy inside I would rather mix in race fuel then any octane booster

But first you need to know what octane your engine actually requires, like others have mentioned that more octane is not always better.

If you have the choice to run less octane safely, buy a different boat, adjust your engines, build different engines, etc. Consider how much actual MPH increase running more octane fuel will produce, is it really worth the headache?

Remember it takes 10 octane "points" to equal 1 actual number, so 7 points raised 89 octane to 89.7.

Also the higher octane you start with the less effective the booster is

I don't agree with "throw in a can for safety" mentality. There are plenty online charts and quick calculation website where you can calculate the exact amount of octane booster or race fuel needed.

Yeah it always "feels" better to error on the high side.

There's lots of sales pitches that say octane booster is more economical, but my calculations show mixing in race gas as being less expensive.

Every option is messy and a pain, octane booster seems easier to carry around at first, but then having a bunch of partial cans rolling around your boat isn't very fun either, so you end up just "pouring" them all in over mixing and wasting money.

When you guys add "race gas", isn't that REAL expensive? I also drag race (mostly 1/8 mile, sometimes 1/4) and the car used C-12 race fuel. Where we buy it, it goes for $11.00 a gallon. Gets spendy in a hurry! How much race gas do you mix in with your regular or premium gas? Is it a ratio, like 2 to 1, or 4 to 1, 10 to 1, of gas to race gas?

Race gas and Octane booster are both "expensive". Utilizing race fuel is a little less then octane booster though.

I've purchased 110+/- race fuel in multiple states range from $7-9/ gallon

Lots of easy online calculators like this

http://www.wallaceracing.com/octane-mix-calc.php

We used to have it available at the pump until recently 107 (I think)

Also have sunoco 113 in 5 gallon pales.

I've always bought vp 116 by the 50-54 gallon drum.

Showing 116 drum at $818.

That's $15/gallon. Cheap insurance. BUT much cheaper to get safe comp ratio IMO

How do you guys running on high octane fuel afford to go boating on a pleasure boat with twins? I easily burn 100 gallons on a weekend with 89 octane. Do you just go to a raft off a couple miles away and hang till dinner?

Offshore..... Nice - thanks for the link!

Go to your nearest airport and get AV gas. It was around $4/gal this summer. Test anywhere from 112-116 octane. And has a little bit of lead in it.

I have used 5 gal cans of 110 before and I do think it would be safer as it's just a mathematical equation but you can't carry it in the boat like a case of qt cans.

Just thought I should throw out this word of warning (from personal experience). Back in 89-90 I was running a 440 Mercury Cyclone engine with multiple power adders, so I decided to experiment with different ways to boost the octane of pump fuel. As most guys I added an octane booster to the fuel, ok so far so good! then decided to continue to use the octane booster and pump fuel along with introducing AV gas to the mix. After sitting for a week I get to the ramp crank the engine over and no fuel pressure, so I'm thinking WTF?? Push the boat over to the beach, remove the mech fuel pump and tear it apart and what I found was crystal type growths on the 4 of the six valves. cleaned them off, reassembled and off we went for the day!! I thought WTF must be an anomaly right? wrong next week go to the ramp crank the engine started fine then proceeded to flood out again I'm thinking WTF. once again push it to the beach remove the Needle and seat and what to my surprise do I find but the same crystal type growths! that happened with one tank over two weeks, never mixed the three again never had the problem again, I could mix any of the two together without issues. So just be careful of what type of science experiment you concoct in you fuel!!