Quote:
Originally Posted by Terry England
The diesels engine needs about 22 to 1 compression ratio to detonate the fuel. To do that you need a long stroke engine or you will put an awfull lot of load on the top end. My "rule of thumb" research is that 3400 RPM Volvos, Yanmars and Vws last 6 to 10 years. 2400 RPM 3208 Cats last 15 to 25 years and 1800 rpm in-line Detroits last 20 - 30 years. If you spool 'em up you'll burn 'em down.
The old 170 Yanmar put out the same torque as a 454 at 3200 rpm's. the problem is the Yanmar was "against the wood" and the 454 was a half throttle. I run them all easy - an engine only has so many "frams" in - no use in using them all up today. Equipment is expensive to replace and It's tough to figure out how to depreciate "toys" with the IRS!!!
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Terry's right, "high speed" diesels often don't last any longer than gas engines, per yacht surveyor Dave Pascoe, who has lots of experience with them and has written
several articles on the subject. He's also addressed the
"Gas vs. Diesel" subject at length.
Although slow speed diesels like the old Ford/Lehman are noted for lasting 6,000-10,000+ hours cruising at 1400 rpm in an 8 kt trawler, that engine only develops 135 HP from 360 Cu. in., or .375 hp/cu in.! The Mercruiser diesel is developing over 1.2 hp/cu in., so if you figure engine life is inversely proportional to hp/cu in., I'd be surprised if it lived for more than a few hundred hrs in a marine application! Although it's performance is indeed impressive, the big question is, for how long?!