Seafari 25 performance

[cdavisdb]

Did an economy run today, 22 miles, F3 stainless props, flat calm, 3300 rpm, 2 adults and full fuel, 2.9 nautical mpg. I am a happy camper. That compares with 2.6 kmpg with aluminum D2s and similar conditions. My old Seabird, shorter, lighter, with the same size engine, did not do this well.

Octane rating apparently makes a huge difference in fuel economy in this engine. The knock sensor enriches the mixture if the engine starts to knock due to low octane fuel. My original fuel test was with mostly fuel from the last owner, who put high octane alcohol fuel in it. I had been putting 90 octane no alcohol gas in. The engine needs 93. Lower octane fuel gave me 2.3 kmpg with the stainless props and somewhere around 2 or less with Bahamian fuel, who knows what octane. Today's run was make with octane booster raising the octane to about 92.

Anybody else have similar results with low octane fuel? Whats the best way to raise 90 octane no alcohol fuel to 93 octane?