Octane questions
 

Hey guys,

I've got a question is regaurds to octane and also ethanol. I have a 500 efi blue motor and I'm wondering which octane I should be running and with or without ethanol. I've done some searching here on the site and it almost sounds like most opinions lean towards regular 87 with my stock blue motor, due to how the ecu (timing) is set up for the burn time of a lesser octane fuel. I also know that no matter what ethanol is a pain in the ass because of the water issues, and can cause no mater which octane it is mixed with to loose up to 10% btu value. Recently this spring, one of the gas stations here started carrying 91 non ethanol, which I have now burnt near 100 gallons of so far this year so most if not all of the old 87 ethanol fuel from last year should be gone. So far everything is just fine but I guess I'm asking which octane is actually better for my particular motor? 91 non ethanol, or 87 with ethanol due to the timing? There is another small mom and pop gas station about 10 miles from my home that is advertising non ethanol but I'm not sure what octane. Would 87 non ethanol be the best if I had that option?

87 non ethanol as 1st choice..........It will leave less soot on the transom and burn more completely
91 non ethanol as 2nd choice.........It will leave a little more soot on the transom
I would avoid ethanol/E10 as much as possible

Are there any side effects that are negative from running the 91 non ethanol?

this is true for any gasoline engine, using an octane higher than you need to keep the engine from knocking will will result in less power and worse economy. Higher octane just makes the fuel slightly harder to light to prevent detonation in high comp or forced induction engines. If your engine doesn't knock on 87 as Griff said that is what you should be using.

Ok, so this might a dumb question, do any companies make an after market programmer, that you could advance the timing and fuel map like ones that are made for bikes, snowmobiles , etc...? Obviously a totally different world, but when I used to be into snowmobiles, I used to use a programmer plugged into the stock ecu, that would do exactly that. We could add or subtract fuel at different throttle positions, and could advance timing for higher octane fuels. Or, could a better idea be to reprogram my own ecu by a reputable motor builder/ dynno shop to do exactly that? Please forgive my ignorance, this is only my second year with my power boat. Depending on being a pain in the rear as far as doing something like this, I'd like to set this up to run the higher octane, non ethanol fuels, do you guys think I'm onto something here or just say heck with it and just pump in the 87/ ethanol in the tank with a smile?

I would contact Whipple Superchargers and see if they have any programs for that motor, I know they do for the 525. If you are between 91 without ethanol and 87 with it, I would also suggest the 91, but you really should try both and see if there is any difference in performance.

What will the gain be--10-30 hp? I don't think you'll see enough gain for the time, money and potential for issues to be worth while in a boat. Now if you start changing cams, heads etc then it would need to be done.
Imho

The only negative effect will be a dirtier transom.

No plug in programmers available.
Whipple can reflash the ECM.
Don't run the 87 E10. It will also vapor lock easier and cause other problems.

Here is my experiance or what I have found with my 502 mpi.

91 non ethanol = engine seemed to be "boggy" and transom was all sooted up witch is a PITA to clean besides the poor fuel economy. But the injectors probably would stay clean. (less maintenance in engine bay)

87 regulator (with ethanol) engine runs strong, Minimal soot on transom, best fuel economy. However up here in "Corn country" we can not get non ethanol gas beside in 91 flavor. Side effect = Vapor locked my VST ALL THE TIME, fuel injectors got plugged easily, since (is my guess) the fuel lines deteriorate quicker. Then the engine runs lean, lean running engine = blowen head gaskets.......

Last off season I had 6 "plugged" injectors, 1 was "so-so", and 1 was "good" according to the injector shop that I sent mine out to for cleaning and flow testing.

This year Im going to try the Mystery oil trick to a tank of gas and see if it will help with vapor lock besides the vst vent, that I vented back to the main tank.

I put about 50 gallons of 87 with ethanol on Saturday. I'm going to try and run that on a couple fill ups to see if I see any differences in performance and cleanliness on the transom. I was also thinking about pulling the injects after this boating season and having then tested and cleaned and of replaced. I'll post my findings in the next week.