I would suggest you consider including a manifold vacuum gage in your instrumentation! (Ask Connor about his experience.) It will give you a good indication of both load on your engine as well as its relative health, and you’ll find that its very sensitive. Reason is that if you want decent life on your exhaust valves, you need to understand that max continuous power = 5 inches Hg vacuum. If your engine is strong enough to cruise at 7” or higher, which it probably is, that’s even better.
A little background info . . . I was an engineer with Pratt & Whitney (maker of the old piston aircraft engines during WWII, before they got into the jet engine business.) for about 35 years before retirement. The modern piston aircraft engines like Continental & Lycoming, which are premium engines with expensive features like sodium filled exhaust valves, positive rotators and Stellite valve seats, are designed to cruise at about 75% power, the max continuous power rating. If you run through the thermodynamic calculations, 75% power works out to about 5” manifold vacuum. Most marine engines do not have those premium features, so many of the engineers I worked with that ran inboards all installed vacuum gages and observed a limit of 5” or higher for cruise rpm, and they expected an engine to run for ~2000 hrs or so before a valve job was required.
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01-15-2022, 10:42 PM
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