Octane which fuel octane level??

quick fuel question,

bought an 04' octane,stock, have always run 91 octane in my sj but after reading the manual for the octane it recommends 87-89 octane..

seeing as i am not as smart as the guys who designed the boat i have run it with that level mixed with high perf synthetic 2 stroke oil at 40:1 as per manual..

performance seems great through entire rev range but being my first octane i have no comparison.

would running 91 octane fuel be detrimental to the engine? or is it actually better.perhaps adding more "snap" to throttle response.

informed answers would be appreciated...would rather it runs fine a long time on 89 then run great on 91 with more rebuilds.

thanks
 

Waternut

Customizing addict
Location
Macon, GA
If you're positive the engine is completely stock, run what the manual tells you to run. The manufacturer won't recommend a fuel that will cause problems with the engine. There is a common misconception that running higher octane fuel makes engines run cleaner, more efficient, and more powerful. Don't believe it.
 
If you're positive the engine is completely stock, run what the manual tells you to run. The manufacturer won't recommend a fuel that will cause problems with the engine. There is a common misconception that running higher octane fuel makes engines run cleaner, more efficient, and more powerful. Don't believe it.


i agree..ive got a 15hp outboard and i actually think it runs a little better on 87 compared to 91... all the high octane does is it burns cooler there for with high compression heads the piston can compress to top dead center and not mis fire..or as its called 'pinging'.
 
The higher octane has a higher flashpoint, so it takes more to ignite it. That's why you can run higher compression and more advance. It doesn't burn "cooler"... The higher octanes do tend to be a little better quality though, and will last longer in storage, for whatever that's worth.
I run 93 in my stock compression Octane all the time. It's not going to hurt anything, but it probably doesn't benefit my much as the gas doesn't sit for long... And you can't really compare the Octane's compression to superjets and such, as our pressure is lower, like 125-140ish psi...
 

DK-Freestyle

2011 World Champion
Location
Oakley, CA
Why not just run 91 to be on the safe side? I tore down a 1200 motor the other day at work and the engine seized up and destroyed the pistons. Customer said he ran the ski hard, and only ran 87 Octane.
 
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