Looking for information on the effects of changing octane in an engine after a significant amount of use. I have an 85 Stars and Stripes, 351W, with roughly 1960 hours. We've done only tune ups and minor repairs (rebuild the starter, replace the fuel pump) since the boat was new. Bought it from my father last year. It's always run on 87 or 89 octane, despite the manufactures recommendation of minimum 93 octane. When I brought it to Wisconsin I have access to 91 octane or 87 with no ethanol. I feel that it likes the 91 better, as it doesn't have that slight hesitation at take off under heavy throttle.
My brother used to work at a marine dealer and was pcm certified. He tells me that you should never change octane after this long on an engine, it's asking for major problems. Car mechanics seem to have never heard of such a thing, but the marine mechanics I've spoken to seem to be split around 50/50 on this. But none can explain why this would cause a problem.
Does anyone have any experience with this? I would love to know if this is a real problem, and if so why. Also, what specific damage would it cause?
I spent most of my money on booze, broads and boats. The rest I wasted. - Elmore Leonard