Gas type to use

[ers906]

Sorry, I meant that I add the stabilizer. It is not necessary since I have to fill up the gas tank at least twice a week for the 8 months + of riding we are able to do here in AZ. Guess I just got in the habit and figure it isn't really going to hurt anything other than my wallet.

[horkn]

I've yet to see a stock or even remotely close to stock ford or GM based ski boat motor need anything more than 87 octane. Even with e10, the 87 works fine, even in my pre knock sensor carbed 351w with higher CR than stock.

[Chexi]

GT-40s say to use 89. I believe you can use 87, but you have to mess with the timing to work perfectly at 87.

[xlair]

I've probably put 2000 hours on GT-40's with nothing but 87 octane. Run fine, never had an octane related problem.

[DanielC]

Do not mess with the timing to run 87 octane on a GT-40. The engine has a knock sensor, and does it automatically. The distributer does not time the engine. The engine's computer does.

You can run 87 octane in a GT-40. The engine may have poorer performance, but not enough for most people to notice. The engine will run better with 89 octane. It might even run better enough to consume fewer gallons per hour.

[Chexi]

Thank you for clearing that up for me. With gas prices going the way they are, I'll probably switch to 87 this summer.