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Old 29-03-2014, 22:40   #1
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Turbo vs normally aspirated

Would appreciate some input from those with experience to share. How much more expensive is it to maintain, over the life of an engine, a turbocharged marine diesel than a comparable normally aspirated engine? Will the turbo-diesel likely require major work before the other? How much more will a complete overhaul run? Obviously the answers would depend a great deal on the specific engines compared so lets start with a yanmar 4JH2-HTE vs a comparable non-turbo yanmar. My experience with gas turbo engines would suggest that the difference in durability, reliability, and maintenance costs would be considerable but there have been so many turbo diesels used extensively in commercial applications for so long that it makes me wonder. In boat shopping, I've been steering clear of the turbos. Should I reconsider? Thanks in advance--
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Old 29-03-2014, 22:45   #2
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Turbo vs normally aspirated

Leave turbos for sports cars, your Audi starts spittin oil or develops a boost issue you can bring it right to the shop. Sure Diesel engines are very reliable with turbos but it's just another failure point. If you have a massive power boat and like spending cash then there tight up your alley. If the budget matters, best to avoid them, money not really a concern, get new ones and let the boost rip.
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Old 29-03-2014, 22:56   #3
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Re: Turbo vs normally aspirated

I'm a car nut and nothing is music to my ears like a spooling turbo and a loud blow off valve. Anything German really. I wouldn't not buy the boat you want because of turbos, but if you don't have one you never have to replace it. Generally a turbo cost less than a injection pump, but might only last half as long. $1000 or so, depending on brand and model. Huge engine, big turbo, more money.
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Old 29-03-2014, 23:30   #4
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Re: Turbo vs normally aspirated

Turbo is pushing up hp available. A low rpm high hp diesel will out live the high rpm light weight turbo boosted one If run properly.
You can get good life from the turbo but running high rpm means more rpm for related horsepower. Someone is going to flame me for this as usual. I have a little more weight with my natural aspirated cummins. But in 1000 hours I have near 1/2 the cycles of a lighter turbo charged yanmar that produces the same hp. Now I'm going to hear my linings are glazed or I use the wrong oil. Well no everything is fine. I see no down side to a non turbo. Except if you want more hp in a smaller footprint


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Old 29-03-2014, 23:56   #5
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Re: Turbo vs normally aspirated

Since diesel engines are essentially air pumps, isn't there an increase in efficiency with a turbo engine?

Let's say one had a boat and it needs a 30 hp N/A diesel turning 2500 rpm to drive it at 9 knots. That same sized engine with a properly sized turbo could make nearly double the torque at the same rpm. Now with the added torque, one could install a higher pitch prop and run at lower rpm, or change gearing to run at a lower rpm for the same shaft rpm. This should result in a net fuel savings, since the turbo engine is turning a lower rpm for the same 9 knot cruising speed.

An added advantage would be if one needed to quickly cover some distance with no wind, you have the power and rpm range to run a higher top speed for the same original rpm that the N/A engine ran at.

It's always interested me that the larger a diesel engine gets, the more efficient it becomes, exactly the opposite of a gas engine. Even though one may only need 30 hp to reach a desired 9 knots, a 100 hp engine may actually be more efficient at that same speed, or even higher speeds. The limiting factor is the rapacious prices they charge for marine diesels!
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Old 30-03-2014, 00:08   #6
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Re: Turbo vs normally aspirated

Would a sail drive give better performance? Could you change the gear ratio? Could you inject nitrous? Sure but you are spinning something more and adding more parts. I'll bet a beta or my cummins will serve longer. I have a sail boat so usually my goal is to be on the water using the sails. I can't think of a time where I needed major hp to push the boat beyond its design speed.


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Old 30-03-2014, 04:04   #7
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Turbo vs normally aspirated

Small turbo diesels this side of the pond are everywhere, they, the turbos are as reliable as the engine and represent no real additional complexity.

Easy to service , any turbo shop here can replace the core for about 150. That's needed at about 4000-5000 hours in some cases. I've just done two large Kkk turbos from Volvo tamd61s for 200 each.

It wouldn't give me a moments thought not to consider a small turbo. Why not improve the efficiency and power output of an engine.

Note high revving has nothing to do with turbos. ( higher compression yes )

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Old 30-03-2014, 04:48   #8
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Re: Turbo vs normally aspirated

Quote:
Originally Posted by sabray View Post
Turbo is pushing up hp available. A low rpm high hp diesel will out live the high rpm light weight turbo boosted one If run properly.
You can get good life from the turbo but running high rpm means more rpm for related horsepower. Someone is going to flame me for this as usual. I have a little more weight with my natural aspirated cummins. But in 1000 hours I have near 1/2 the cycles of a lighter turbo charged yanmar that produces the same hp. Now I'm going to hear my linings are glazed or I use the wrong oil. Well no everything is fine. I see no down side to a non turbo. Except if you want more hp in a smaller footprint


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The above is is my take on it... I own both T and NA
Buy the boat you like... T or NA, the powerplant is probably sized well for the boat... Unless of course it's a bad repower, or a bad one off...
Me? I'd lean towards large lower rpm T...

(edit.... My juvenile mind enjoyed seeing T and NA repeated upon proofing...)
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Old 30-03-2014, 05:14   #9
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Re: Turbo vs normally aspirated

Let's talk specifically about the 4JH2-HTE engine. It is a 2 liter, 4 stroke diesel. In its normally aspirated form it makes about 53 hp. The HTE version is turbocharged and aftercooled and makes about 100 hp. I think but am not sure that the HTE is seawater aftercooled.

So, given the above, how much horsepower are you going to demand from that engine. The most I would want to pull from that engine long term is 60 hp and that is about 2,700 rpm. Any higher and you are above the magic 30 hp per liter that the gurus on boatdiesel think is the dividing line between continuous cruising and a blast at high rpms for an hour or so once in a while.

How heavy a boat and what waterline length are you looking at and how fast do you want to cruise. That will determine the power required. Post some numbers and I will figure it for you. But it takes a big sailboat to require more than 60 hp at cruising speed.

I am going out on a limb here but I think that you can get several thousand hours cruising at that load and combined with idling, getting in and out of the anchorage, etc your engine could go five thousand hours with good maintenance and correct proppng.

Given that it is seawater aftercooled you will have to remove, disassemble, clean, lube and replace the aftercooler every 3-5 years, but otherwise there is no other special maintenance. Turbos themselves can go the life of the engine. Turbos get wasted in marine use due to sea water backing up into them due to bad exhaust design and not the fault of the turbo.

The engine is compact and is a good choice as a sailboat auxiliary. If you are going to operate more like a trawler or at higher power loading then I would look at something with more displacement like a John Deere. But a normally aspirated JD in that hp range will have twice the displacement, weigh twice as much and probably won't fit in most sailboat's engine rooms.

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Old 30-03-2014, 05:35   #10
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Re: Turbo vs normally aspirated

Quote:
Originally Posted by sardinebreath View Post
Would appreciate some input from those with experience to share. How much more expensive is it to maintain, over the life of an engine, a turbocharged marine diesel than a comparable normally aspirated engine? Will the turbo-diesel likely require major work before the other? How much more will a complete overhaul run? Obviously the answers would depend a great deal on the specific engines compared so lets start with a yanmar 4JH2-HTE vs a comparable non-turbo yanmar. My experience with gas turbo engines would suggest that the difference in durability, reliability, and maintenance costs would be considerable but there have been so many turbo diesels used extensively in commercial applications for so long that it makes me wonder. In boat shopping, I've been steering clear of the turbos. Should I reconsider? Thanks in advance--
I just had a 4JH2-DTE 88hp turbo-diesel completely rebuilt and the turbo cost was about 10% of the total so I don't think the additional cost is very significant compared to the benefits of smaller size and weight for the same horsepower available, along with greater efficiency. I had it rebuilt after buying the boat used, not because the engine or turbo was failing, but the previous owner had it WAY overpropped for the last 15 years and at some point had a seawater leak in the engine compartment that sprayed water around causing numerous rust spots. But the engine was still operating just fine. I plan to keep the boat for awhile and wanted to start fresh so made the decision to pay Mack Boring to essentially make the engine like new. I can't speak to the long term reliability of them but if the turbo does eventually fail, the engine will still get you home, and the cost of a turbo rebuild isn't that high. Buy the boat you like best and at least for me, the question or turbo or non-turbo isn't even on the radar as a consideration.
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Old 30-03-2014, 05:59   #11
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Re: Turbo vs normally aspirated

Highly redacted summary for you...

Quote:
Originally Posted by Horror Hotel View Post
I wouldn't not buy the boat you want because of turbos, but if you don't have one you never have to replace it.
Quote:
Originally Posted by sabray View Post
I see no down side to a non turbo.
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(from a guy who loves his turbo)

Quote:
Originally Posted by goboatingnow View Post
It wouldn't give me a moments thought not to consider a small turbo.
Dave
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Quote:
Originally Posted by HappyMdRSailor View Post
Buy the boat you like... T or NA, the powerplant is probably sized well for the boat... Unless of course it's a bad repower, or a bad one off...
Quote:
Originally Posted by jtsailjt View Post
Buy the boat you like best, and at least for me, the question or turbo or non-turbo isn't even on the radar as a consideration.
5 flips of the coin give the same message... Both from turbo and NA owners.... Buy the boat you like...
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Old 30-03-2014, 06:14   #12
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Re: Turbo vs normally aspirated

Personally being a diesel mechanic I would prefer no turbo as once you have turbo problems your toast out there. With a pump or injector issue I can limp in. Here in Canada the fellow before we bought our boat had to install a new turbo, that once done was around, $2,500, something I think was a bit over priced. Myself I always consider if it breaks what can I do to get by, if turbo is gone nothing.
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Old 31-03-2014, 22:01   #13
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Re: Turbo vs normally aspirated

Thanks for all the input, folks. I suppose that I wouldn't let a turbo dissuade me from a boat that I otherwise coveted but there doesn't seem to be much consensus about how much extra trouble/expense/risk a turbo might present and whether or not it's worth it. Again, if I was looking for reliability and maintenance economy, and basing my decision on what I know about gas engines, I wouldn't get near a turbo. I find it difficult to believe that a turbo diesel going to go as long between overhauls as an N/A, but the number of TDs utilized in commercial trucking makes me wonder about that.
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Old 01-04-2014, 04:02   #14
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Re: Turbo vs normally aspirated

Turbos on petrol engines are generally used to boost performance and are fairly high pressure.

Turbos in diesels are primarily for efficiency and then to be lower pressure.

Here in Eu'rup TDs are the norm and user experiences is that the turbo lasts as long as other major parts of the engine.

Oil change regimes do need to be maintained

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Old 01-04-2014, 10:41   #15
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Re: Turbo vs normally aspirated

[QUOTE=goboatingnow;1506758]
Here in Eu'rup TDs are the norm and user experiences is that the turbo lasts as long as other major parts of the engine.


I think I'm less concerned with whether or not the turbo wears at the same rate as the rest of the engine, than I am with the effect of the turbocharger on the rest of the engine, i.e., do TDs tend to get fewer hours between overhauls and tend to suffer more mechanical problems than NADs? Perhaps I should query shops that rebuild both.
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