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Old 03-16-2016, 03:55 PM   #1
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Turbo vs NA

Sorry guys, Some of the replies from my last post prompted me more questions, and I feel like it should be a separate thread:

"We cruise at 2700 rpm and the turbo kicks in somewhere over 1000 rpm or so"

I read some engine can be either turbo or natural, like John Deere 4045DFM70. But what does that mean? Does it mean:

A You can buy the engine in either turbo or natural configuration, but once you purchased it, you cannot change it.
B You can buy the engine and install it as turbo or natural(maybe by adding a turbo component?), but once install is done, you can't change it
C You can flip it back and forth between turbo or natural by pressing a magic button or sth, turning on some kind of "turbo component" in real time
D The engine itself determine whether it needs to run in turbo or natural mode, open the throttle to certain point, and the engine will switch automatically from natual to turbo
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Old 03-16-2016, 04:06 PM   #2
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But what does that mean? Does it mean:

A You can buy the engine in either turbo or natural configuration, but once you purchased it, you cannot change it.
You can buy it one way or another - depending upon the exact engine you can change some non turbo engines to a turbo engine with enough money and time, But much better to buy it that way originally.

B You can buy the engine and install it as turbo or natural(maybe by adding a turbo component?), but once install is done, you can't change it
As above - here are some engines which could have turbos and cooolers added , but why buy one way and then change?

C You can flip it back and forth between turbo or natural by pressing a magic button or sth, turning on some kind of "turbo component" in real time
No magic button for you to hit.

D The engine itself determine whether it needs to run in turbo or natural mode, open the throttle to certain point, and the engine will switch automatically from natual to turbo
No magic engine button for engine to hit either.
But .... on an engine that has a turbo at lower speeds/loads it will not add boost so the affects of the turbo are mostly 'off'. At higher speeds/loads the boost will build and the turbo affect will be "on".
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Old 03-16-2016, 04:43 PM   #3
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I don't believe you can buy a newly-built, naturally-aspirated JD 4045 anymore, leastwise in the USA. Fortunately, the NA version was available when purchasing mine.
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Old 03-16-2016, 04:48 PM   #4
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I have a 4045. When I bought mine 2 years ago, the tier 2 engines had ended production in the USA. To the best of my knowledge, there are no tier 3 non tubos in the size range we use. Too difficult to make them tier 3 compliant. Not saying that you might not be able to find one used or rebuilt, but no new production of non turbo 4045s in the USA.

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Old 03-16-2016, 05:12 PM   #5
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boost is load dependent not rpm dependent. out of gear at max rpm there is no boost because there is little load and fuel. Load the engine and more fuel is needed thus more exhaust and boost. A magic switch is unnecessary.
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Old 03-16-2016, 05:33 PM   #6
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Thanks for the explanation.

It's sad they stopped producing it. Hope yanmar dont follow the suit!
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Old 03-16-2016, 06:06 PM   #7
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Newer engines are designed from the ground up to be turbocharged and after cooled, like the Cummins QSBs. Older engines started life as normally aspirated engines and were redesigned to be turbocharged. The Perkins 6.354 is an example of this.


When the engine designer adds a turbo and after cooler he usually does all or some of the following: reduces the compression ratio, installs a different injection pump, re plumbs the raw and coolant water systems, installs different injectors, installs oil cooling jets under the pistons to control heat, etc, etc.


You can buy a NA block and add all of the above stuff yourself, but it will cost a fortune in parts and labor.


Not sure about your Yanmar comment. The only NA engines that Yanmar still makes are the YM and JH sailboat engines at 57 hp max.


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Old 03-16-2016, 06:21 PM   #8
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My 37hp Mitsu (S4L2) is a tier 11 and no longer availible as a propulsion engine but I'll bet it's being sold as an auxiliay gen engine. And that is probably the case w all the rest. If one was clever (and many here are) a NA propulsion engine could be done.

There's always DD.
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Old 03-16-2016, 09:31 PM   #9
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Quote:
Originally Posted by chicagoq View Post
Sorry guys, Some of the replies from my last post prompted me more questions, and I feel like it should be a separate thread:

"We cruise at 2700 rpm and the turbo kicks in somewhere over 1000 rpm or so"

I read some engine can be either turbo or natural, like John Deere 4045DFM70. But what does that mean? Does it mean:

A You can buy the engine in either turbo or natural configuration, but once you purchased it, you cannot change it.
B You can buy the engine and install it as turbo or natural(maybe by adding a turbo component?), but once install is done, you can't change it
C You can flip it back and forth between turbo or natural by pressing a magic button or sth, turning on some kind of "turbo component" in real time
D The engine itself determine whether it needs to run in turbo or natural mode, open the throttle to certain point, and the engine will switch automatically from natual to turbo
I'm going to differ slightly on my answer to your questions form some of the preceding answers.
Turbocharging as a technowledgy is fairly poorly understood by many and I won't try and explain it here as there are many resources on the web you can look up Cummins Turbo Technologies -> Products & Technologies -> Turbocharging Explained -> How a Turbocharger Works.

A. Yes you can buy an engine that is either naturally aspirated or turbo charged and you can change it after you have it either way. It's not so simple with marine engines and in particular newer technowledgy engines but engines such as the Cat 3208 or Cummins 6bta used to be available in either configuration. On small trucks I have added a turbo charger kit specifically made for that installation in a day with only slight udjustments to the injection pump settings. It's not nearly so easy for a marine application.

B. See the answer to A and again not so easy for a marine engine. I should also qualify my answers with the fact that this is possible where I live but subject to local environmental regulations may not be legal where you are.

C & D. Contrary to the belief or some a turbo charger usually does not turn on or off or cut in a a specified RPM. A mechanical supper charger can and a turbocharger can be partially controlled by a waste gate but at almost all RPM's above idle it will be spinning and therefore compressing air. It's only really efficient at doing this under load and at higher RPM but it is providing compressed air to the induction side of the engines up to ambient pressure (nominally 29.9 inches of mercury or 14.7 PSI) which is the limit for a normally aspirated engine. Above ambient on marine engines the pressure is normally messured in PSI and this is what is termed boost (boost above ambient)

A turbocharged engine of the same basic type should almost always be more efficient that it's normally aspirated mate as it is recovering energy free from the exhaust and using it to make power. The amount of difference will be determined how it is loaded and run.

Cheers

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Old 03-16-2016, 10:15 PM   #10
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No trouble to buy and install a naturally aspirated John Deere in Australia, in the smaller sizes, if you want. They have a D suffix, and are M1 or M2 rated only. The 4045D is 85HP at M2, and the 6068D is 125HP at M2.

But a new boat built in Australia with these engines installed might not be able to be legally imported into Europe of USA. Although if registered elsewhere then it should be able to visit for limited periods at a time.
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Old 03-17-2016, 03:30 PM   #11
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So looks like natural is going out of fashion quickly.

Would one be able to convert a turbo engine into a NA? I understand there will be HP loss, but suppose one can live with that? Is it also going to be very expensive? Would I be able to have the kind of longevity enjoyed by a real NA engine?
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Old 03-17-2016, 03:45 PM   #12
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Why this notion that turbos shorten diesel engine life? There are millions made this way every year. However, it is true that bad exhaust designs can allow water leaking back into the induction system thus require a turbo replacement at best and a new engine at worst.
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Old 03-17-2016, 04:44 PM   #13
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Quote:
Originally Posted by chicagoq View Post
So looks like natural is going out of fashion quickly.

Would one be able to convert a turbo engine into a NA? I understand there will be HP loss, but suppose one can live with that? Is it also going to be very expensive? Would I be able to have the kind of longevity enjoyed by a real NA engine?
It many cases there are different components. The pistons on "B" series Cummins are different between turbo and non turbo. I imagine the injectors and injector pump are also. Possiblly different exhaust and intake manifolds also.

It's reasonable to expect 10,000+ hours out of a standard (not high performance) turbo diesel. In most boats, that's 2 or 3 owners. If you think your going to put those kind of hours on a motor, then make sure it's sleeved, so that it can be rebuilt.

Quote:
Originally Posted by sunchaser View Post
Why this notion that turbos shorten diesel engine life? There are millions made this way every year. However, it is true that bad exhaust designs can allow water leaking back into the induction system thus require a turbo replacement at best and a new engine at worst.
Think part of the bad rap comes from High output motors. When you take a NA motor around 150 HP, turbo it and get 210 HP out of it, it will have a nice long life. Crank it way up until you're getting over 400 HP out of it, and, well it's not going to live a long life.

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Old 03-17-2016, 09:48 PM   #14
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Quote:
Originally Posted by chicagoq View Post
So looks like natural is going out of fashion quickly.

Would one be able to convert a turbo engine into a NA? I understand there will be HP loss, but suppose one can live with that? Is it also going to be very expensive? Would I be able to have the kind of longevity enjoyed by a real NA engine?
I'd agree with the other guys here that turbos get a bad rap on many occasions because they are set up badly with exhaust elbows etc and then some people will overload them and run them into the ground.

If you don't need the extra horsepower and the engine is set up well, just buy the turbo charges version and after it has been run in correctly put a boost or manifold pressure gauge in it and don't run it above ambient. This idea that you have to run a turbo charged engine at high power every now and then is pretty much rubbish. Don't take my word for it have a look at what Tony Athens says on his web site at Seaboard Marine.
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Old 03-18-2016, 07:05 AM   #15
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"Why this notion that turbos shorten diesel engine life?"

The turbo allows more power to be pulled from an engine per hour..

As engine life is better measured in fuel burn than hours , burning more fuel per hour will shorten the time - in hours- to the rebuild.

Some turboed engines have the compression lowered to allow for more fuel burn with out detonation.

These do not do well when run at tiny power where the turbo is not putting out pressure enough to overcome the lowered compression..
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Old 03-18-2016, 09:29 AM   #16
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Detonation is not a diesel engine phenomenon, applies to spark engines only.

Don't confuse high output turbo engines meant for go-fast boats and turbo engines meant for continuous duty. The continuous rated engine will last dang near forever like a NA engine.

Lowered compression leading to poor low power burn is an issue with high output engines. Continuous rated engines run lower boost and the compression ratio is similar to the NA versions.

If you want an engine designed for long life, get one rated for continuous duty and ignore whether it has a turbo or not.
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Old 03-18-2016, 09:38 AM   #17
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"If you want an engine designed for long life, get one rated for continuous duty and ignore whether it has a turbo or not."

How do I know a engine is designed for continuous duty? Is there a special name of keyword I should look for? Or do you have an example of one of those engines?

Thx!
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Old 03-18-2016, 09:40 AM   #18
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All engines whether with a turbo or not are designed to operate most efficiently at specific loads and rpm. Some of the designs have longer and flatter best output curves but they all favor one area or another. When you know how you will use your boat most of the time that will tell you what kind of hp you will be demanding from the engines. At that point you can find the fuel use vs hp curve for various engines and see what the differences are whether turbo or not. Often you will read that a typical 4 stroke diesel will produce 20 hp per gallon of fuel used per hour, or 18 hp per gal of fuel used or even 16 hp or less per gallon of fuel used.
What is not usually known is that all of those numbers can be correct for the exact same engine dependent upon the exact load and rpm you are measuring at.
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Old 03-18-2016, 09:56 AM   #19
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How do I know a engine is designed for continuous duty? Is there a special name of keyword I should look for? Or do you have an example of one of those engines?

Thx![/QUOTE]

Go to the boat diesel website and look under "engines" Pick the brand you are interested in and voila, all sorts of information will appear including M, hours allowed per day at what throttle setting and continuos duty ratings.

In today's modern engines most ratings are altered by a chip which essentially is a hand on the throttle.

If you want to know if a particular engine is destined for long life a good tell is whether or not it has been designed for larger genset or off highway use.
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Old 03-18-2016, 02:55 PM   #20
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"Detonation is not a diesel engine phenomenon, applies to spark engines only.
"
Images for diesel engine detonation damage
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