After reading specification sheet on hundreds of boats in Powerboat Reports, Power and Motor Yachts, etc for years, and seeing figures basically the same for a 350 chev, regardless of the boat it's in (same for big blocks) both of your figures sound pretty optimistic, unless you're staying below 2,500rpm. That ain't a bad idea,,,,come to think about it!
Bob
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I carry a gun because it's too tiring carrying a cop.