So I found a local gas station who has ethanol free gas but it's 91 octane. I'm thinking about switching my outboard 90hp boat, push mower and tractor to ethanol free. Is it worht the extra cost of 91 octane? Doesn't really matter for the tractor and the push mower as it won't be that much more, but it's the boat. I want to keep the engine clean as long as possible.