Thread: Under propped?
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Old 03-15-2014, 05:54 PM   #27
namsutol
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City: Bethesda md.
Country: us
Join Date: Jul 2013
Posts: 11
torque and egt

My boats been overpropped for all its 200,000 miles, with an average of 5.5mpg (including genset use) 25,000 hours on the last engine which was replaced by a JD 4045D/80hp due to lack of support/spares by MANN.

What I found is that the 16 hours out of 24 (m1-m2-m? stuff) is related to Exhaust Gas Temps, which for a dumb Deere is limited to about 1100 degrees-maintaining that 24/7 will burn exhaust valves( meaning loss of compression and the associated costs) EGTs=load.

The torque peak (the twisting/screwing force) on the Deere is 1200-1400rpm and it diminishes after that point-the HP goes up but the torque drops. All diesel engines develop max torque at lower rpm than max HP.

On a 40ft waterline, 40,000 pound boat I do 7.1 knots at 1200rpm-8.4 at 1400rpm. my EGTs are 500-650 degrees-running a 32/28 3 blade and 2.85 reduction-IF I ran a sub 28 inch prop I could hit my engines "redline" of 2400rpm- and be outside of the torque peak.My valves will never burn out-my water temps are 175-180. No smoke issues.

If you read your EGT-and operate your boat in the meat of your torque curve, not your HP curve, and adjust your injection pump timing, the degrees BTDC when it squirts you get it all, economy, power and longevity.

This is not rocket science-Engine manufactures want you to engineer your boat to their engine-for emissions.

or you can tune their engine to your boat.

That's my 2 cents-most will disagree
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