Originally Posted by v666
Do any outboards have an ecu that can adjust the engine to make use of the higher octane fuel?
If not, why would anyone bother to use higher octane fuel that you will never have any benefit from.
Without having a scantoool to monitor the engine diagnositics, it's hard to tell whether their would be a benefit other than cleaning out the fuel system.
General motors (and many other car mfr's) use a "knock" sensor to monitor detonation. It's a band pass microphone that looks for resonant tones that indicate when teh fuel/air mix is not behaving and lets the ECM know when that happens. The ECM in turn reduces spark advance to eliminate the knock(which lowers power, blows head gaskets, hammers bearings, etc...). However, the spark timing values come from a fixed table and the ECM will not increase spark timing on it's own beyond the values in the table.
If todays marine motors use a knock sensor...
If you have a boat with a few more people on it than normal, or a higher pitch prop that loads the engine enough to drop RPM's then I would bet that SOME detonation is occuring and spark advance is being pulled out...
It would be worth testing with Xylene or Toluene to see whther there was an improvement in performance under heavy load conditions.