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Old 04-05-2013, 09:22 AM   #1
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6cyl or 4cyl diesel main engine

I've been looking at Deere engines and they have a 6cyl and the newer generation 4cyl that are similar horse power. The 4cyl will be electronically controlled and the 6cyl is not. Both are turbocharged. It seems to me that the 4cyl would be better on fuel consumption. Anyone have any opinions on the pros and cons for this? I do have an email started with the Deere salesman to see what he says.

Here is my current thoughts:
The electronic 4cyl adds complexity
The 4cyl would be lower MPG
The 6cyl would be quieter (wild guess)
A physically smaller engine give me more space
I will soon know the weight and cost difference
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Old 04-05-2013, 09:30 AM   #2
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Why turbocharged?
IMO htat may be a bigger issue.
I do agree with your 4 vs 6 points you brought up.

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Old 04-05-2013, 09:47 AM   #3
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Why turbocharged?
IMO htat may be a bigger issue.
I do agree with your 4 vs 6 points you brought up.

Richard
It looks like both of the engines they offer would be turbocharged. This is the 150hp to 175hp range. I might just be stuck with a turbo.

I just have the slight fear that I would be overworking a 4cyl and the 6cyl would have an easy time with the load. That might just be my resistance to new things!
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Old 04-05-2013, 09:59 AM   #4
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It looks like both of the engines they offer would be turbocharged. This is the 150hp to 175hp range. I might just be stuck with a turbo.

I just have the slight fear that I would be overworking a 4cyl and the 6cyl would have an easy time with the load. That might just be my resistance to new things!

Which is the old proven engine with some history? I would not have an electronic controlled main engine, and if possible non turbo. the only reason we bought a single engine is because it’s a DD 671 which has a long history, reliable, and parts and serve.

Make sure the engine has enough HP for future requirements like hydraulic, stabilizers, big alternator, cruise gen etc. Better to have to much HP and not enough!
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Old 04-05-2013, 10:04 AM   #5
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What type and size of boat?
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Old 04-05-2013, 10:06 AM   #6
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What size boat?

A 40 foot trawler only needs about 40 hp....I'm pretty sure the 39 Kady Krogens came with an 80hp John Deer standard when they first came out.

When I repower I am gonna try to dro down below my 120hp Lehman.

I would go with the 4...they run 4s and 3s on lotsa construction equipment (light towers, gensets, etc) that go forever under pretty harsh use.
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Old 04-05-2013, 10:37 AM   #7
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The 4cyl should be fine

Quote:
Originally Posted by mikesacs View Post
Here is my current thoughts:
The electronic 4cyl adds complexity
The 4cyl would be lower MPG
The 6cyl would be quieter (wild guess)
A physically smaller engine give me more space
I will soon know the weight and cost difference
I too was worried about electronics, but according to the engine dealer, they just don't have problems with them.

My JD 4cyl is smoother and quieter than the Lehman it replaced. It actually has more power, and I wish it had less. I'm only loading the engine to 30% at normal cruising speeds. A little higher load would keep the exhaust temperature up where I don't have to worry about condensation in the turbo.

I would think the fuel economy on the 4 would better, not worse.

The shorter 4 gave me room to put a starter battery in front of the engine between the engine stringers. That allowed me to tie the two 8D's together as one house battery, doubling my house capacity.

The JD + battery was about the same weight as the Lehman. I didn't have to add ballast.
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Old 04-05-2013, 10:40 AM   #8
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In this case it is a clear choice between an electronically or mechanically controlled engine.

For me personally, the choice is not difficult, mechanically.

A boat is not a truck, no roadside repairs possible.

At a cost of Diesel I prefer old technology with more easy repair on the fly.
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Old 04-05-2013, 12:28 PM   #9
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The 4cyl/6cyl question is a bit complicated.

Most 4s will have more vibration but there are many variables that can alter the amount of vibration. Flywheel and crankshaft weight, injector timing capabilities, compression, combustion chamber design, operating rpm and many other features could alter the amount of vibration felt on the boat. Structural features of the boat like stiffness, size and location of bulkheads and other flat parts of a hull can be resonate to the # of cylinders and/or the operating rpm. Some engines like the 4cyl JD engines have balancers that can be quite effective. Some balancers are only effective at certain engine speeds and some are not very effective at all. But as most anyone here can guess the 6 cyl engine is usually noticeably smoother than a four especially of the same size.

The bore/stroke relationship is the most controlling element of the choice to use more or fewer cylinders. Piston speed on a diesel is probably even more of a factor that it is in gas engines because the piston needs to be much heavier and longer. Not many short stroke diesels and short skirt pistons in the diesel world. But (all other things being equal) the more cylinders the lower the piston speed and thats very important. Ever heard of a 6 cyl 20hp diesel? probably not. Ever heard of a 1cyl 40hp diesel? Bigger cylinders produce more torque, better fuel economy and less power (hp). More cylinders w less piston speed and smaller pistons produce more power. Note that when Detroit Diesel wanted more power they went to great lengths to have as many cylinders as possible. Harley's don't have much power but they have plenty of torque. 10,000rpm motorcycle engines w 4 or 6 cylinders make eye popping power but have little torque.

Engines w a given number of cylinders tend to have a fairly confined range of power especially those that operate at the same rpm. I know of no 4 cyl 25hp diesel engines. No 6 cylinder 50hp engines either. Many of us have engines at the upper or lower limit of the cylinder class or group such as my 4 cyl 40hp engine. It's at the bottom of the 4 cyl range. So it has some 6 cyl personality traits. The 135hp JD is at the upper 4 cyl range. So it assumes the "personality" (to a maximum degree) of an engine w large and few cylinders. The personality of trawlers is best suited to the personality of engines w bigger and fewer cylinders.

So if you're looking for an engine that maximizes economy, smoothness, hp per pound of weight, inexpensive price (new), size ... especially length and width and compatibility w a given boat AND are looking for an engine in a power range where you actually have a choice (like 100hp) you have the power to maximize the special requirements you have. Like a high speed trawler would want more cylinders (shorter stroke and smaller pistons), inline configuration for fitting into a smaller boat w more servicing room around the engines, less weight higher rpm be damned. But a passagemaker leaning trawler will want economy of fuel burn above all else and an engine w fewer cylinders will most often be best.

Notice I did not mention turbos as there are many subjective opinions about them but a turbo version of a given engine can put it in a different category that may introduce or eliminate the 4cly/6cyl choice.

All the above is my own opinions and facts and just for conversational purposes here on the forum.

mikeacs,
The 4 cyl will usually give better economy re fuel burn.
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Old 04-05-2013, 12:48 PM   #10
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Originally Posted by psneeld View Post
What size boat?

A 40 foot trawler only needs about 40 hp....I'm pretty sure the 39 Kady Krogens came with an 80hp John Deer standard when they first came out.


My 35-foot, 14-ton boat has a non-turbocharged, non-electronic, 4-cylinder, 80 HP John Deere 4045. At normal cruise speed, one knot below hull-speed, it runs at 1800 RPM generating 68 HP . To generate 40 HP, it is only running at a high idle of 1000 RPM out of a maximum of 80 HP at 2400 RPM.
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Old 04-05-2013, 01:23 PM   #11
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Mark my 40hp Mitsu is 107 cu in. What's the displacement of your Deere?
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Old 04-05-2013, 01:30 PM   #12
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My Deere is 275 cubic inches. Believe my engine (max 2400 RPM) runs slower than yours.
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Old 04-05-2013, 01:42 PM   #13
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While I know turbochargers are the way these days to get more power and efficiency from a smaller, lighter engine, my experience in operating engines with turbochargers/superchargers on them, primarily in aircraft but a bit in boats, too, is that superchargers are wonderful when they're on somebody else's engine.

They're a high heat, high speed device that tends to have a service life much shorter than the engine it's bolted to, and they are expensive to fix or replace.

We continue to kick around the idea of repowering our GB and if we do one of the criteria for the new engines would be natural aspiration. Lugger used to make a wonderful 150 hp straight six, NA diesel that was used in a lot of repowers including a lot of GBs. Unfortunately they no longer offer this engine.

Don't get me wrong. I think turbochargers are great in terms of what they accomplish. But I want them to accomplish it on somebody else's dime. This is one reason that when we specced our new Ford pickup we immediately dismissed the so-called "EcoBoost" engine which sports not one, but two turbochargers. So twice the repair/replace expense.

As to the number of cylinders I have always heard/been told that a six-cylinder in-line engine is about as smooth running a configuration as you can get with the exception of a V-12, which is simply two of them joined together. Not to say a four won't last every bit as long and be every bit as reliable. But in vehicles, anyway, the fours always seem a bit rougher and more "uneven."
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Old 04-05-2013, 01:49 PM   #14
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Declined the builder's option of having the turbocharged version of the JD.
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Old 04-05-2013, 03:02 PM   #15
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Declined the builder's option of having the turbocharged version of the JD.
Good reason is that you don't need and can't even use more than 80hp.

Yes my Mitsu makes it's 40hp (37 in a universal industrial rating) At 3000 rpm.
And is less than half the cu in disp. I see on the JD site your engine makes
40hp ........ at 1000 rpm
50 hp ........ at 1500 rpm
55 hp ........ at 1850 rpm.
And of course 80 hp at 2500 rpm. All these hp ratings are at WOT.
The prop curve (not at WOT but a simulated boat load) shows 31 hp at 1000 rpm but that's probably for a typical boat and yours is more efficient (being FD) so running along in your Coot the engine is probably working at about the 27 or 28hp level.

You've got just about the perfect trawler Mark.
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Old 04-05-2013, 03:16 PM   #16
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What size boat?

A 40 foot trawler only needs about 40 hp....I'm pretty sure the 39 Kady Krogens came with an 80hp John Deer standard when they first came out.

When I repower I am gonna try to dro down below my 120hp Lehman.

I would go with the 4...they run 4s and 3s on lotsa construction equipment (light towers, gensets, etc) that go forever under pretty harsh use.
It's a Bruce Roberts 44' boat with a 48,000 lbs displacement. The designer recommends 120 to 175 hp. I tried to narrow that down to 150 - 175 to compare engine types.
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Old 04-05-2013, 03:21 PM   #17
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I too was worried about electronics, but according to the engine dealer, they just don't have problems with them.

My JD 4cyl is smoother and quieter than the Lehman it replaced. It actually has more power, and I wish it had less. I'm only loading the engine to 30% at normal cruising speeds. A little higher load would keep the exhaust temperature up where I don't have to worry about condensation in the turbo.

I would think the fuel economy on the 4 would better, not worse.

The shorter 4 gave me room to put a starter battery in front of the engine between the engine stringers. That allowed me to tie the two 8D's together as one house battery, doubling my house capacity.

The JD + battery was about the same weight as the Lehman. I didn't have to add ballast.
Is your 4045 a turbo?
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Old 04-05-2013, 03:49 PM   #18
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Manyboats, I don't know the reason for the horsepower variances. My information comes directly from the JD owner's manual.
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Old 04-05-2013, 03:55 PM   #19
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Declined the builder's option of having the turbocharged version of the JD.

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.

------------------

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/engi...045DFM7080.pdf

-----------------------------------
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Old 04-05-2013, 04:13 PM   #20
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Quote:
Originally Posted by Marin View Post
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.

------------------

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/engi...045DFM7080.pdf

-----------------------------------
I would tend to agree, I have had 3 diesel pickups and put many miles on them and have never had any issues (knock wood) with any of the turbos. Don't even know they are there. On the one I drive now I did put a boost and EGT gauge in since I put a chip in. Boost rarely goes up unless you really punch it and EGTs are usually below 800F. Only once was it up to about 1200 on a 3 mile uphill grade pulling a 15,000 lb fifth wheel. Lots of power. It didn't scare me to buy my boat with a turbo 6 cyl. Runs smooth.
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