Downrated HP?

An ad in the classifieds says "210 hp at 2,800 rpm, but actually downrated to 150 hp to enhance even further long time reliable service."

Explain, please, the who, how, why.

Hawgwash said:

An ad in the classifieds says "210 hp at 2,800 rpm, but actually downrated to 150 hp to enhance even further long time reliable service."

Explain, please, the who, how, why.

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Ask the same of seller. Sometimes it is nothing more than throttle stops other times a bizarre thinking tear out of "bigger" injectors, removal or turbo, bigger prop etc. I'm always leery of these owner induced changes. Cat or Cummins?

Obviously pulling back on the throttles does the same thing.

3208 injection pump can be set at a lower max fuel rate to limit hp. Or underprop. Or pull the throttle back. All do similar things.

sunchaser said:

Ask the same of seller. Sometimes it is nothing more than throttle stops other times a bizarre thinking tear out of "bigger" injectors, removal or turbo, bigger prop etc. I'm always leery of these owner induced changes.
Obviously pulling back on the throttles does the same thing.

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Thanks.
I didn't want to clutter the ad posting with a potentially naïve question as it sounded to me like it was a known/common thing with some kind of authentication.
Guess not.

Actually, if de-rated properly it allows you to 'over' prop (more pitch) and aim for a design point lower on the engine's power curve, using more of the available power and torque at lower RPM. This usually puts you in a slightly more efficient operating regime in terms of specific fuel consumption (grams of fuel / hp/ hr) as an added bonus. Nice thing to do if you're not obsessed with top speed, and further points to this being a 'proper trawler'.
Most engines are offered at several ratings, with pleasure boats being allowed to squeeze more power out at higher RPM since they don't do it for as many hours as commercial operators. The downside there is you're 'required' by the mfr to prop the boat for that top RPM, which means less pitch, which means you get less out of the engine at that mid-range RPM you actually prefer to use.

From memory, de rating means changing the physical specs of an engine to lower its HP rating. However people changing these numbers to suit their needs smacks of covering up deficiencies. Buyer beware.

cappy208 said:

From memory, de rating means changing the physical specs of an engine to lower its HP rating. However people changing these numbers to suit their needs smacks of covering up deficiencies. Buyer beware.

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Ok, so what would an engine surveyor have to say about it?

It's been a long time, but if memory serves me, the first HP versions of that engine design were below the widely popular 210 rating. I believe we actually owned a 160 and 175 version early on in Ford straight trucks, and I think that Oliver/White Tractor had it at 150 or below. Injector and pump settings.

This sounds like perhaps an old continuous duty 3208.

Hawgwash said:

Ok, so what would an engine surveyor have to say about it?

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It would depend on if they even knew how to tell. Without knowing the actual engine parts it's hard to tell. Physically de rating an engine means either removing the air blower/ turbo, or installing thicker liners and smaller Pistons. What is usually done is lowering the RPMs.

The 'why' is the skeptical part. I have heard of more than one person saying 'I de rated l my engine' and what they meant was its overheating and I don't / can't figure it out so I run it slower to get it to not blow up. BUT..... I am a skeptic!

Many engines are MFG rated for service , from pulling water skilers up to 24/7 .

M-1 to M-4

The engine is identical, only the paperwork suggests the HP that can be used for a specified length of time.Tranny gearing and prop selection set HP.

This is why so many folks will chose a cruising prop, good long term operation at an efficient quiet RPM, and no harm with the seldom seem 1 nm/g dash once or twice a year.The "pleasure boat" rating for modest time does zero harm to the engine.

This is what the ad says;
"Single Caterpillar 3160 renamed to 3208 in 1974, w/o any technical changes to 3160. 210 hp at 2800 but actually downrated to 150hp..."

I'm not looking to dis the seller here, just trying to learn why and how this would be done.

The word "downrated" is probably not the right word. The 3160 had a different fuel pump than the 3208 and the 150 hp rating was probably a use rating direct from Cat without alteration. This particular 3160 @ 150 hp was a common engine in the PNW fishing fleet. I owned the first marine version of the 3160 with the new fuel pump before they changed name to 3208. It was one of 4 trial engine with the new pump. Three engines were placed in land use and mine was the marine version. The serial number on my engine identified it as a 3160 but all of the parts on the engine were 3208. Made for some interesting times when ordering parts from Cat.

Hawgwash said:

This is what the ad says;
"Single Caterpillar 3160 renamed to 3208 in 1974, w/o any technical changes to 3160. 210 hp at 2800 but actually downrated to 150hp..."

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If you look at any marine engine from most of the mainstream marine manufacturers, you'll see different classes of engines, from 24/7 to 200 hours per year of estimated service.

To make a 24/7, they 'derate' or limit the performance in the injection pump or CRD fuel computer controller so it won't output as much as a 4 hours on, 20 hour off engine.

As FF quoted, John Deere has M1-M4 ratings:
M1 <= 65% load factor, unrestricted hours, continuous duty, 154hp output
M2 <=65% load factor, 16 per 24 hour day, 3000-5000 hours annually, 175hp output.
M3 <=50% load factor, 4 hours per 24 hour day, 2000 - 4000 hours annually, 200hp output.
M4 <= 40% load factor, 2 hours per 24 hour day, 1000-3000 hours annually, 225hp output

I'm curious about this. Saw the following quote on the Seaboard Marine web site a few weeks ago. They don't say how it's accomplished, but it's interesting that they offer it as an option.

Heavy Duty Commercial Grade Cummins 6BT 210 Marine Engine Packages

The Cummins 6BT 5.9 is a rock solid and simple engine... Plus, the engine is easily de-tuned if less than the maximum 210HP is needed.

stubones99 said:

If you look at any marine engine from most of the mainstream marine manufacturers, you'll see different classes of engines, from 24/7 to 200 hours per year of estimated service.

To make a 24/7, they 'derate' or limit the performance in the injection pump or CRD fuel computer controller so it won't output as much as a 4 hours on, 20 hour off engine.

As FF quoted, John Deere has M1-M4 ratings:
M1 <= 65% load factor, unrestricted hours, continuous duty, 154hp output
M2 <=65% load factor, 16 per 24 hour day, 3000-5000 hours annually, 175hp output.
M3 <=50% load factor, 4 hours per 24 hour day, 2000 - 4000 hours annually, 200hp output.
M4 <= 40% load factor, 2 hours per 24 hour day, 1000-3000 hours annually, 225hp output

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And as long as it's done at the factory, it's going to give you a longer lasting more reliable engine in most circumstances. But when it's done after market or by an owner, then I'd personally be very leery of it as they often have only done part of the job.

MTU rates based on both the type and amount of usage and the type boat it's being put on. That's because they design for high speed boats and at the other extreme for low speed continuous use heavy work boats. Most engines we see in marine applications are also used in industrial applications and there they have much different ratings and set ups.

Somewhere in marine applications you'll see a big difference too is the same base engine used for boat propulsion vs. used for generators.

The only difference between a Perkins Sabra 265hp and 300hp was 1/4 turn to a screw on the fuel pump and the stickers on the engine. Yes, I did own one.

My Cummins is governed to 2150 rpm and produces 250hp at that RPM. It is M1 and can run there 24 hours (which I don't ever do except for testing as the fuel burn is breathtaking). My friend has two identical engines rated at 420 hp at 2800 rpm but only for a couple of hours. I suppose I could claim "I have a Diamond Series Cummins derated to 250 hp."

Old deckhand said:

The only difference between a Perkins Sabra 265hp and 300hp was 1/4 turn to a screw on the fuel pump and the stickers on the engine. Yes, I did own one.

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This is all very interesting.
So what did that 1/4 turn do to performance?

"Single Caterpillar 3160 renamed to 3208 in 1974, w/o any technical changes to 3160. 210 hp at 2800 but actually downrated to 150hp..."

I had a bus with a 3160 and although it was just like the 3208 it was a far different block.

The 3160 actually had cylinders with liners , could be inframed in place.

The usual use of these was in skool buses where rebuilding is seldom done , just R&R , throw it away, as the funds are almost unlimited.

The throwaway 3208 fit the service use far better and was much cheaper to build.

150 HP is optomistic , the coach was fine on flatland FL but died in the hills .

A 210 HP DD 6-71 seemed easily 2x the power .

The ratings M1 to M4 are for the exact same engine , only change is the service setup required (tranny and prop) for the desired service.

Most DD can be changed by advancing or retarding the can timing and installing different injectors to suit the HP desired.

Hawgwash said:

This is all very interesting.
So what did that 1/4 turn do to performance?

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I never turned screw. I do not know if the present owner has turned the screw.

Turning the screw depends on the injector pump. Some 'screws' adjust the travel or stops of the pump stroke length. Others have individual capacity adjustment per cylinder. And CRD engines have a computer that adjusts everything based on everything. They have sensors for intake air temp, exhaust temp, and torque sensors. Some have knock sensors to adjust the timing to limit engine knocking.

I don't think I would turn a screw a quarter round unless I knew what it did on the inside.

"The ratings M1 to M4 are for the exact same engine, only change is the service setup required (tranny and prop) for the desired service."

I have a different turbo than the Diamond series, which might suggest its more than just the ancillaries that are different?

On the power plant in my 'other' boat I have 2150hp EMD-12-645s X2.

The model is rated at 2150. It has a turbo.

The lowest model (using the same exact block) uses just air blowers (NO turbo) and is rated at 1950.

The model after that has larger blowers and is rated at 2025hp.

The model with the highest HP has blowers AND Turbos and wrings 2350HP out of these blocks.

All this is measured at 900 RPM.

So the difference in rating comes from the factory. I am suspect of 'someone' who says 'they have Derated their engine'. It's not that simple.

Pulling back the throttle stops is not 'derating'. It just taking it easy on your engine.

There's some iron ballast.

The turbos are around 3' in diameter. The air boxes are 3' square.

cappy208 said:

I am suspect of 'someone' who says 'they have Derated their engine'. It's not that simple.

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Perhaps "someone" has been following this and will comment.

cappy208 said:

View attachment 46448View attachment 46449View attachment 46450
There's some iron ballast.

The turbos are around 3' in diameter. The air boxes are 3' square.

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Great stuff.
What are they pushing and what are the insulated lines on the back wall/bulkhead?

chriscritchett said:

Actually, if de-rated properly it allows you to 'over' prop (more pitch) and aim for a design point lower on the engine's power curve, using more of the available power and torque at lower RPM. This usually puts you in a slightly more efficient operating regime in terms of specific fuel consumption (grams of fuel / hp/ hr) as an added bonus. Nice thing to do if you're not obsessed with top speed, and further points to this being a 'proper trawler'.
Most engines are offered at several ratings, with pleasure boats being allowed to squeeze more power out at higher RPM since they don't do it for as many hours as commercial operators. The downside there is you're 'required' by the mfr to prop the boat for that top RPM, which means less pitch, which means you get less out of the engine at that mid-range RPM you actually prefer to use.

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Boy Chriscritchett, you have succeeded IMHO, in collapsing the massive discussion on over wheeling with this response. All that you write in a concise manner is what I had been attempting to state over several post regarding propping with over size wheel while still maintaining a cushion of 400/500 RPM to WOT. At this setting the boat is obtaining hull speed at a very, very quite and comfortable sound level, close to fuel burn of similar engine/hull configuration running manufacture recommended wheel which is reflected in operating RPM range and corresponding fuel burn. With my over wheel application I burn approximately a quart more than the other example. Acceptable for the results, he is screaming along at 1800 RPM against my 12/1300 RPM at the same hull speed. Good trade off, Thanks for the post.
Al-Ketchikan

The shot of the side of the engine? On the aft bulkhead is the 4" and 6" bilge, ballast and fire lines. All painted either white or red.

The insulated lines on the overhead are the potable hot and cold water lines insulated so they don't freeze in the winter when the faucets are shut off.

Currently pushing 100,000 bbls of diesel. 4,200,000 gallons

cappy208 said:

The shot of the side of the engine? On the aft bulkhead is the 4" and 6" bilge, ballast and fire lines. All painted either white or red.

The insulated lines on the overhead are the potable hot and cold water lines insulated so they don't freeze in the winter when the faucets are shut off.

Currently pushing 100,000 bbls of diesel. 4,200,000 gallons

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Cool, thanks for showing us your rec room.