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Old 04-12-2016, 11:01 AM   #13
Ski in NC
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City: Wilmington, NC
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 6,194
Some of the inefficiency comes from pumping losses, but most comes from how low the effective compression ratio is when throttled. Efficiency is highly correlated with comp ratio. Throttle the inlet and CR drops way down.

One boat on the dock has a carb'd gas Chrysler 318 with a flowscan on it. When rev'd to 1000rpm in neutral, it is burning 1.1-1.2gph. Owner says his flowscan has proven pretty accurate. So 1.5gph on a bigger engine that is still "tight" from rebuild sounds about right.
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