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Old 07-18-2019, 12:05 AM   #1
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Cummins QSB 5.9 HO

Greetings. Can someone shed some light on the difference between the HO (high output) version of the Cummins QSB 5.9 and the non-HO version of that same engine?

Assuming that the engines are equally responsibly maintained and run for a similar number of hours per year, should I expect any significant difference in maintenance needs or longevity?

How about performance characteristics? Is one appreciably quieter? Smoother? Should I expect a significantly different fuel burn on the HO version?

I ask because Iím looking at two boats that are substantially identical except for the fact that one has a QSB 5.9 305 and the other has a QSB 5.9 330 HO. Both engines appear to have been impeccable maintained.

What are the relevant differences between the two engines that I should know about? Thanks very much in advance.
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Old 07-18-2019, 02:11 AM   #2
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You need to look at sbmar.com, there’s a section called Tony’s Tips, and a Q and A section too. Should be able to get the info you need there, Tony Athens is a very reputable and knowledgeable Cummins expert.
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Old 07-18-2019, 05:25 AM   #3
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First there may be no difference between the two engines you are considering, just a different hp measuring protocol. If there are any differences it is just electronic and the 305 hp one can probably be programmed to match the 330 hp engine's output. But there is no need to do that as the 305 can be run at the same cruising hp output as the 330- in the low to mid 200s.

Some years ago when the QSBs first came out, I spoke to Tony Athens about the differences among the various QSB models at that time which ranged from about 200 to 370 hp. He said that there were no mechanical differences among them and if you bought a 200 hp model you could later have a Cummins tech reprogram it for 370 hp- for a substantial fee.

That is very different from the older Cummins Diamond engines where the 210 hp one had no after cooler and the 370 hp one had a sea water cooled after cooler among other differences in turbo output, injector delivery and maybe even piston oil cooling.

There should be no maintenance differences between the two QSB engines as they have exactly the same internal mechanicals.

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Old 07-18-2019, 05:28 AM   #4
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The 305hp is a lower rating than the 330, and thus has a less restrictive duty cycle to get engine long life. No significant changes in the actual engines, just different fuel maps and maybe a turbo. Difference only matters in the warranty world and if you run the engines at high power setting. In a trawler where engines are run easy, there is basically no difference. And both are conservative ratings. The same basic engine is also rated at 380, 425 and 480hp.
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Old 07-18-2019, 07:56 AM   #5
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The 305hp is a lower rating than the 330, and thus has a less restrictive duty cycle to get engine long life. No significant changes in the actual engines, just different fuel maps and maybe a turbo. Difference only matters in the warranty world and if you run the engines at high power setting. In a trawler where engines are run easy, there is basically no difference. And both are conservative ratings. The same basic engine is also rated at 380, 425 and 480hp.
May have different injectors. More HP means needs more fuel injected and maybe more air so higher boost pressure. I have the diesel truck 5.9 HO with 325 hp and been learning more about them, and I think they are a great engine.

Tell me, is a marine turbocharger insulated or water cooled to prevent exhaust heat from the engine room on the cummins 5.9?
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Old 07-18-2019, 08:06 AM   #6
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May have different injectors. More HP means needs more fuel injected and maybe more air so higher boost pressure. I have the diesel truck 5.9 HO with 325 hp and been learning more about them, and I think they are a great engine.

Tell me, is a marine turbocharger insulated or water cooled to prevent exhaust heat from the engine room on the cummins 5.9?
With the advent of electronically controlled common rail injection as is on the QSB, it is not necessary to have different injection pumps and injectors for various hp ratings. The electronics controls the fuel delivery over a wide range of hp loadings.

Cummins QSB turbochargers like most Yanmars, Cats and Volvos are water jacketed. I think that there is a larger displacement Cummins model that is insulated and it is known for gasket failures. FWIW Yanmar in the early days of its BMW based engines didn't jacket or insulate the manifold or the turbo. They soon discovered that this was a huge problem for boat applications and recalled and retrofitted insulation on those motors.

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Old 07-18-2019, 08:59 AM   #7
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There do seem to be many combinations in different engines.


The Cummins QSM11 (11 liter) has water jacketed manifold and turbo in the continuous duty power rating, but dry manifold and turbo (insulated) in the high output ratings.


My Scania DI13 (13 liter, continuous duty rating) is jacketed manifold, but dry (and insulated) turbo.


Those are just a few that I've encountered.
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Old 07-18-2019, 09:47 AM   #8
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I was asking similar questions about the Cummins QSB 5.9L engine. The used boat I purchased has a 380hp version of that engine. The manufacturer originally specíd the 330hp HO engine, but the original owner asked for the 380hp version.

As was mentioned, the difference between the 330 and the 380 is primarily the fuel map. The HO engines are not continuous duty and designed for no more than 1 hour of full power operation for every 8 hours of operation. Reduced power needs to be at least 200 rpm below max.

The 305 hp version is a ďmedium continuous dutyĒ engine. This is rated for 6 hours of full power operation for every 12 hours of operation. I believe the 305hp version is also turbocharged.

The basic engine is the same. I donít believe (check with the folks at Seaboard Marine) there is any difference between the two. If you need the extra power, go with the 330hp. If you donít need the extra power, I donít think it matters which engine you choose. When run at lower power levels they would perform the same. I also think (but check with folks that know) that when run at lower power levels, the duty cycles will be the same. In other words, if you run a HO engine at lower power levels, you will get the same longevity as a medium continuous duty engine run at lower power levels.
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Old 07-18-2019, 09:53 AM   #9
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Originally Posted by djmarchand View Post

With the advent of electronically controlled common rail injection as is on the QSB, it is not necessary to have different injection pumps and injectors for various hp ratings. The electronics controls the fuel delivery over a wide range of hp loadings.

Cummins QSB turbochargers like most Yanmars, Cats and Volvos are water jacketed. I think that there is a larger displacement Cummins model that is insulated and it is known for gasket failures. FWIW Yanmar in the early days of its BMW based engines didn't jacket or insulate the manifold or the turbo. They soon discovered that this was a huge problem for boat applications and recalled and retrofitted insulation on those motors.

David
Well you can get higher hp injectors and they flow more without modifying the computer asfaik. But you can also mod the computer. I read about injectors on the Cummins forum. Someday I may need new injectors and would not get stock, would get the slightly higher hp ones. The forum also said they can get better mileage. Spray pattern injection timing, duration, and multiple injections during combustion. Higher pressures are coming going to 60000 lbs someday for greater efficiency.
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