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Old 01-01-2010, 06:06 PM   #2
Nomad Willy
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City: Concrete Washington State
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 18,743
RE: HP vs. RPM vs. Economy

Hey TJ,
Your part 2. Wev'e beat that one into the ground over time. See the old posts. I think so but I'm not totally convinced and others don't think so and I'm sure they aren't totally convinced. Two things will be well worth considering. Very few of us have known of engines that have died from underloading (I have) but on the other hand all modern and most all older diesel engines can operate happily, dependably and economicaly at very high levels of loading (in the range of 80-90%). I think a diesel engine should be run around 70% load.
Heavily loaded gasoline and diesel engines are about the same in efficiency but lightly loaded diesels are much more efficient than lightly loaded gas. The difference is highly related to fuel mixture over a range of load.
Big engines loafing are quite pleasant but less efficient for two main reasons. There is much more friction in the large engine (even turning higher rpm) but most importantly there is much or much much more surface area to disipate* heat. And since wer'e talkin about heat it should be remembered that heat loss is directly related to efficiency. Tough questions but there are many known facts. Good luck with it.
Eric Henning
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