Turbo Diesels

My John Deere 4045 diesel is absent a turbocharger (YES!). No longer available without the turbo due to government regulations.

sunchaser said:

Don't DD 2 cycles require a very mild boost super charger due to need for scavenging?

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Yes they do. If you know how 2 strokes work, there is some valve overlap....IOW an intake valve and an exhuast valve may be open at the same time. Add to that the compression of a diesel engine and you do not want the fuel charge to take the path of least resistnance. Enter the supercharger....all it does is keeps the the gases(exhaust or otherwise) going in the proper direction.

To the OP.....this is a valid point to your thread. Detroit Diesels are considered "naturally aspirated" even though they have superchargers. The supercharger is not there for the sake of increased power. It is simply there to keep the gases flowing in the proper direction on a 2 stroke engine. They are in the 1-3psi range.....whereas turbos are in the double digit range.

Fletcher500 and I were making a joke. Turbochargers are not really evil but making more than 1 hp per cubic inch might be evil or it might be a lot of fun.

There are no intake valves in a 2 stroke DD, there are intake ports in the side of the cylinder barrel.

Baker said:

Yes they do. If you know how 2 strokes work, there is some valve overlap....IOW an intake valve and an exhuast valve may be open at the same time. Add to that the compression of a diesel engine and you do not want the fuel charge to take the path of least resistnance. Enter the supercharger....all it does is keeps the the gases(exhaust or otherwise) going in the proper direction.

To the OP.....this is a valid point to your thread. Detroit Diesels are considered "naturally aspirated" even though they have superchargers. The supercharger is not there for the sake of increased power. It is simply there to keep the gases flowing in the proper direction on a 2 stroke engine. They are in the 1-3psi range.....whereas turbos are in the double digit range.

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sean9c said:

There are no intake valves in a 2 stroke DD, there are intake ports in the side of the cylinder barrel.

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I agree.

Turbo or not is irrelevant, or at least misleading. What matters is the duty rating of the engine, and how it’s run relative to that duty rating.

There are plenty of turbo charged, continuous duty rated engines that operate at full power all the time when underway. And they last for 10s of thousands of hours.

IMO turbos are very little problem. After coolers that go with them are a different story.

bayview said:

IMO turbos are very little problem. After coolers that go with them are a different story.

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Yes, and that is why marine Turbos sometimes get a bad wrap because boat owners don’t follow the proper maintenance cycles required on the after coolers. On my QSB/380 the manual says 3 years for the AC service but I had it pulled early at 2 years and sent to the radiator shop for cleaning and pressure testing to be proactive, see the internals, and to get a baseline because it’s still relatively new. It was bolted back on last week. Some recreational boaters and many of the commercial operators do theirs annually which is also recommended by Tony Athens. The Cummins shop in my area is very experienced and they feel 3 years is fine so that is what I am going with going forward, and that will also include the Trans Cooler and Heat Xchanger.

As a point on engine design being a major factor in longevity, look at a modern Cummins QSB. Even in the 400+ hp ratings, they have a good reputation for longevity. Depending on the generation of engine, they're either 5.9 or 6.7 liters. In comparison, a 6-71 displaces 7 liters. And turned up to 400+ hp, they're often referred to as time bombs. But turn the power levels down and the 6-71 will live at least as long as the Cummins and probably outlive it. All just a function of what the engine was designed to do and what its weak points are at higher power levels.


Fletcher also has a great point about maintenance. The harder an engine is pushed and the more parts you add, the more sensitive it is to good maintenance. At a point, you end up with an engine that'll run forever with the white glove treatment, but can be killed very quickly by poor maintenance and abuse / inattentive operators.

twistedtree said:

Turbo or not is irrelevant, or at least misleading. What matters is the duty rating of the engine, and how it’s run relative to that duty rating.

There are plenty of turbo charged, continuous duty rated engines that operate at full power all the time when underway. And they last for 10s of thousands of hours.

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This is what I would like to find in writing. Any ideas where something like that might be in one place? or what search terms I would use? I'm looking at trawlers from 36-45 ft. Typical fare. Under $150,000, so older tech.
no need or desire for DD 2 stroke. I do know how loud they are, I lived on a boat with a Coast Guard station in the harbor. I know the sound of an 892 in my sleep.

The manual for my Yanmar 6LPA-STP 315 HP (254 cubic inch) turbo charged diesel says to run it five minutes WITH NO LOAD before shutdown.

Turbo cooldown is pretty meaningless on boats. By the time you come off power and get into the slip and get tied up in most all situations the engine has idled way plenty to cool the turbo down. And most of these are water cooled (wet) turbos that cool down quick.

On a car or pickup or road tractor while towing on a hot summer day, and pull into a rest stop to pee, then cooldown can be a concern. And most of those are dry turbos which do get hot.

Regarding turbos and longevity: Any engine, whether turbo or not, running at a high specific hp (that is hp per liter) is not going to live that long. Run at low specific output and they live very long. It is that simple.

Almost all modern engines above say 100-200hp are now turbo. They do make them more efficient. And the turbos are very reliable. Just keep the sea water out of them!!!

Indeed. A bigger problem than turbos IMO is poor exhaust design allowing water back into the engines.

Obviously an idle 20 minutes up a creek or harbor will do the same as idling at the dock. But some folks think in literal terms and that's what makes us all slightly different and interesting. I know that solid materials hold heat and cold. So, massive iron exhaust manifolds, etc will benefit from additional cool down time. Is it literally necessary? Is it 5 minutes or 20 minute? there's no one correct answer. But the general concept of not being overly concerned or obsessive is a fair attitude to take and enough for me.

Ideally, if you have an egt gauge, I'd figure 30 seconds to a minute after the egts are no longer meaningfully dropping and you should be as cool as the turbo is going to get.

sean9c said:

There are no intake valves in a 2 stroke DD, there are intake ports in the side of the cylinder barrel.

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Still my point for the supercharger is the same....to keep positive pressure on the fuel/air charge going in the desired direction. Otherwise there is the potential for exhaust gases to go in the wrong direction.

Well, just about every manufacturer spec sheet that I've seen has had the engine ratings on them so you could start there.
If you want to find a lot of information on different engines and their outputs in one place try boatdiesel.com. I think you have to but a subscription in order to view engine data but it's cheap.

Swfla said:

This is what I would like to find in writing. Any ideas where something like that might be in one place? or what search terms I would use? I'm looking at trawlers from 36-45 ft. Typical fare. Under $150,000, so older tech.
no need or desire for DD 2 stroke. I do know how loud they are, I lived on a boat with a Coast Guard station in the harbor. I know the sound of an 892 in my sleep.

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Swfla said:

This is what I would like to find in writing. Any ideas where something like that might be in one place? or what search terms I would use? I'm looking at trawlers from 36-45 ft. Typical fare. Under $150,000, so older tech.
no need or desire for DD 2 stroke. I do know how loud they are, I lived on a boat with a Coast Guard station in the harbor. I know the sound of an 892 in my sleep.

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You have to realize that diesel engines in a recreational boating application are rated pretty much as highly as they can get away with and still get through the warranty period. Continuous duty commercial engines are potentially the same engines that are de rated both RPM and power. SO running them more gently and the engine will last for quite a long time.

$25 annual for boat diesel.com is reasonable, Thanks.

I'm pretty sure ISO sets a rating criteria.

Baker said:

You have to realize that diesel engines in a recreational boating application are rated pretty much as highly as they can get away with and still get through the warranty period. Continuous duty commercial engines are potentially the same engines that are de rated both RPM and power. SO running them more gently and the engine will last for quite a long time.

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I wanted to thank you all for taking the time and interest in my posts. Your responses guided me toward discovering other sites thru google. I feel confident about turbo diesels as a whole. It also opens up more boats to choose from. A good problem to have!

sean9c said:

I'm pretty sure ISO sets a rating criteria.

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You missed my point

From a higher end marine engineer about not cooling modern turbo diesels.......


"A gazillion boats with EMD engines might argue otherwise, they are all fitted with "soakback pumps" to both prelube the turbo before starting and to run for a few minutes after shutdown to cool the turbo bearings and seals."

[emoji2962][emoji2962][emoji2962]

Fletcher500 said:

Turbos are evil. I would never buy an engine with one.

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rslifkin said:

Ideally, if you have an egt gauge, I'd figure 30 seconds to a minute after the egts are no longer meaningfully dropping and you should be as cool as the turbo is going to get.

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Yes - that is exactly what we have seen running EGT gages for so many years.

After looking at several spec sheets, I see how continuous duty is detuned from recreational, thus a built in safety to increase longevity. As mentioned rec use is maxed out tuning. I also see a couple of models available with three different turbo/hp setups. Common sense tells me to pass on the top powered setup. I also now understand why the gears and prop setup need to have the engine run the required rpms to have the engine loaded. So much more to learn.

Bligh. I was joking. See post #26.

When our boat was being built we could have specified any engine we wanted. I went with Cummins for various reasons. I never considered a continuous duty engine for a recreational boat. Its just not needed for 99% of us, myself included.

Swfla said:

After looking at several spec sheets, I see how continuous duty is detuned from recreational, thus a built in safety to increase longevity. As mentioned rec use is maxed out tuning. I also see a couple of models available with three different turbo/hp setups. Common sense tells me to pass on the top powered setup. I also now understand why the gears and prop setup need to have the engine run the required rpms to have the engine loaded. So much more to learn.

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It is not necessary to run at high load. Just back off to continuous duty power and you have a continuous duty engine. I dont see the advantage of continuous duty engines in non commercial pleasure boats that will see a few hundred hours use per year unless you are buying it for your grandchildren..

Swfla said:

After looking at several spec sheets, I see how continuous duty is detuned from recreational, thus a built in safety to increase longevity. As mentioned rec use is maxed out tuning. I also see a couple of models available with three different turbo/hp setups. Common sense tells me to pass on the top powered setup. I also now understand why the gears and prop setup need to have the engine run the required rpms to have the engine loaded. So much more to learn.

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Just because you may choose a QSC600 over a 500, it doesn’t mean you have to run it up there. But it’s there if you need it. And if the 500 is truly the exact same engine as the 600 with a tune, then you have a good idea how hard you can run that 500hp engine. There be no problem with running it at max continuous.

Baker said:

Just because you may choose a QSC600 over a 500, it doesn’t mean you have to run it up there. But it’s there if you need it. And if the 500 is truly the exact same engine as the 600 with a tune, then you have a good idea how hard you can run that 500hp engine. There be no problem with running it at max continuous.

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I guess, on paper, running rpms below target speed will encourage soot buildup. Maybe in actual use, it's not an issue until you've reached 5000 hours (random number). This "on paper/in theory" is a trap I don't wish to fall into. But it's hard to tell which posts are real world vs theory. Most everyone states their opinions as black and white fact.