Received this regarding my comments on turbochargers from my engine industry friend. Seems my perceptions are a bit off the mark. Thought it might be of interest to the rest of you.
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Marin---
Turbocharging isn't necessarily a bad thing. It is a frequently misunderstood thing though, that is for sure.
Here are some numbers that might be of interest to the forum member you mentioned with the NA John Deere engine in his Seahorse Marine boat.
His normally aspirated engine has a compression ratio of 17.6:1
The turbo version has a compression ratio of 17.2:1
His normally aspirated engine can produce a full load EGT of 1139F.
The turbocharged version will produce a full load EGT of 770F.
The turbo version "breathes" better. The exhaust valves run cooler because valve overlap bathes them in cool air for a period on each exhaust stroke.
The turbo version is capable of producing more horsepower, but that doesn't mean you need to use it.
Turbos on gasoline engines live in Hell and are routinely operated by drivers who treat them like they are a carburetor or a radiator. Ignorance is bliss until the costs of abuse are presented.
Turbochargers lead a relatively comfortable life on a diesel and can easily last the life of the engine, if for no other reason than the way the engine in a recreational "trawler" is operated, long periods at moderate power with an extended period of "cool-down" before the engine (and its lube oil supply) is shut down. Replacing the turbo on a JD 4045 only costs around $700 or so in any event. That should not scare anyone away from higher efficiency and greater available power.
The fear of turbos and the common belief of high expenses and dangers from mistreatment simply don't apply to the units fitted to small diesels on recreational vessels, trawlers in particular.
Here is a PDF with the power specs for the John Deere engine in question.
http://www.deere.com/en_US/docs/eng...R/perf_curve_documents/PT2_01-4045DFM7080.pdf
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