The Difference between Continuous/Marine Ratings

[50BMG]

Hello,
I was wondering what the real difference between continuous or marine performance ratings and automotive or trucking performance ratings . I know that there is a substantial difference but I don't know exactly what it is. I hope that someone on this website can enlighten me. Thanks in advance for any thoughts, opinions, or answers.

 

[The patriot]

Not sure if this is what youre looking for but....marine ratings are probably higher partly because they have an endless cooling system.

 

[50BMG]

I know that most marine engines have a cooling system with unlimited amounts of cold water so they wouldn't get overheated as fast. But what about the continuous use engine power ratings ? Since most of them lack this kind of cooling system ?

 

[DonFitzwater]

Marine ratings have nothing to do with available cooling. The ratings are rpm related....more specifically, high rpm continuous duty. Automotive and truck applications will spin up to higher Rpm during acceleration and then drop off rpm in high or top gears. Marine engines have no gears like an automobile and must scream for speed.

I run across people every year that think a Chevy 350 is a Chevy 350.......not so when it comes to marine application. Marine (as well as certain industrial) engines provided by GM come factory equipped with "dimple" rods, 4 bolt main caps (not all but most....Volvo had some 2 bolt main 305 and 350's back in the day), stiffer valve springs and cams much better suited for breathing at high rpm. Certain engines will also have brass freeze plugs, stainless steel head gaskets and other goodies. Automotive spec'd engines will usually be short lived in a marine environment. Even the paint jobs are different.

 

[RustyJC]

Marine ratings of turbocharged diesel engines have everything to do with cooling. (My company, before I retired, manufactured marine engines.) Marine engines have an infinite supply of cool water to hold down coolant, lube oil and intercooler/charge air temperatures, so can operate at higher BHP levels at lower air manifold temperatures than engines that use liquid-to-air or air-to-air heat exchangers.

Yes, there are other differences as well, but cooling is a major one.

Rusty

 

[EDankievitch]

​There is a huge difference between European Marine engines and American Marine engines. In Europe where fuel is much more expensive than here they rate their engines at 90% load but for only 10% to 20% duty cycle. Here we rate our engines for 90% load 100% of the duty cycle. Volvo Penta ran in to issues back in the early days. They would rate an engine at 200 Hp it would be almost half the weight of a 200 Hp Cummins or Detroit Diesel. Yes it would put out 200 Hp but would come apart in short order where that Cummins or Detroit would just take the load and keep right on running.
Marine engines have a hugely different load cycle than a highway engine. In an over the road truck the demand to climb that hill is only for a few miles most of the load is wind resistance when on flat highway. In a boat that "Hill" never ends the boat is always trying to climb up it. Don't believe me next time you'rout on your boat under way pull the throttle back and drop it right into neutral and see how fast it slows down. Having that huge mass of cooling water does help with heat. But there is No substitute for heavy over built castings and bearings.
As for the GM 350's with two bolt mains they are still out there and running in boats. There were a few Chrysler 318's with two bolt mains also. The difference is the Chrysler blocks were way over built compared to the GM's. In my marine career I've seen many 318's with way over 3000 hours of running time on them rarely do you see a GM with over 2000 hours on it. unless it's had upper end work.

 

[50BMG]

Thank you DonFitzwater that was EXACTLY what information I was looking for. I was thinking about swapping a marine grade engine into a truck, do you think this would be applicable or a good idea? I know that if it was in a truck it wouldn't have load on it all or most of the time like it would if it was in a marine or industrial environment.You know more about this than me.

 

[SnoKing]

As stated above marine engines are ALWAYS run up hill. ME have governor's to limit max RPMs. Cummins rated my B150 for continuous operation 200 RPM below the 2800 max. And allow full operating RPM for something like 5 hours out of 24. Cooling is a big issue, as the later B250 4 cycliner model burnt down number 4 cycliner because the heat exchanger was under rated for the extra 100 HP.

I ran my B150's for 19 years and 2800 hours with only replacing one coolent circulation pump, starter relays, and thremostats in both engines, and normal maintenance before selling the boat last year.

 

[AH64ID]

Continuous is just one of several marine ratings, so the two aren't really comparable. https://cumminsengines.com/ratings-and-definitions

One distinct difference between marine and OTR/pickup engines is the variable load difference. Once installed in a vessel marine engines will generally see the same load at a given rpm with only a small variance. i.e. at 2,000 rpms the load will always be the same. Propeller demand at rpms below rated rpms is always much lower than capable power for that rpm and there is no way to increase the load at a given rpm. A OTR/pickup can go from 0%-100% load at practically any rpm, which means there are cooling, oiling, longevity, etc issues to be concerned with. 500hp at 1,000 rpms is much hard on components than 500hp at 3,000 rpms.

Marine cams/turbo's generally would be very laggy if they where used in OTR/pickup as they don't need full power until rpms are near rated rpms. The curve below is the QSB480, which is the highest rated OEM 5.9 made. It uses a HX55 with a large turbine housing, so just imagine trying to tow at GCWR with a HX55 single.

This curve is a great example of the difference between propeller demand and available power. Once installed the engine operates on the propeller demand curve (± a variance, but props are designed/modified to allow the engine to run at rated rpm at WOT), not the dyno curve.

 

[DonFitzwater]

Thank you DonFitzwater that was EXACTLY what information I was looking for. I was thinking about swapping a marine grade engine into a truck, do you think this would be applicable or a good idea? I know that if it was in a truck it wouldn't have load on it all or most of the time like it would if it was in a marine or industrial environment.You know more about this than me.

it really will depend on what engine brand/type you are looking to swap into a truck. I know some 5.9 b's have different compression ratios......what type engine are you swapping?

 

[50BMG]

I was thinking about swapping in a 4BTA Cummins.

 

[DonFitzwater]

You may want to do a little homework and compare injection pump and compression ratios to an engine from a bread van or similar. Not sure what engine you are looking at but most of the 4bt's I looked at have been from air compressors and light plants.

 

[50BMG]

I've been looking at Seaboard Marine they have a 4BTA that they claim puts out 250 Horsepower.

 

[petersonj]

I was thinking about swapping in a 4BTA Cummins.

It probably is not too well known, but back in the mid 80's Cummins offered a 4BT or a 4BTA diesel engine that would fit behind small block engines for Ford, Dodge, and Chevy pickups. The kit included a bell housing adapter and flex plate for automatic transmissions and the engine was EPA certified for all 50 states at the time. The engine could be purchased to mate with an automatic or a manual transmission.

From the 1984 to 1994 I lived in Leadville, Colorado at 10,000 feet in elevation. I drove a 48 mile round trip to work at Copper Mountain Resort (at 9,600 feet) and back, crossing over Fremont Pass (twice a day) at 11,300 feet. My primary vehicle was a 1984 Ford E150 passenger van with a 300 cubic inch in-line six cylinder engine. Naturally aspirated engines gasped for air at those elevations. I had always thought that a small turbocharged diesel engine would be a shining star in performance for this application.

So, one day in 1987, a Cummins rep was delivering a diesel engine that provided auxiliary power for a small ski lift at Copper Mountain. The engine weighed 2,500 lbs and was being delivered in the bed of a 1985 Ford F250 2WD which was powered by a 4BTA Cummins engine mated with a Ford C6 automatic transmission. After some conversation with the Cummins rep, we took the truck for a test drive up the 7% grade toward Fremont Pass with me at the wheel. I came to a complete stop with the truck about half way up the grade. Starting from a standstill I was able to get back up to 50 mph. I was impressed.

In 1988 I made a decision and purchased a 4BTA (rated 120 hp @ 2500 rpm, 315 lb/ft tq @ 1700 rpm)
engine kit from Cummins for $5,300 and I swapped it with the engine in my van which by 1988 had logged 118,000 miles. It turned out to be an excellent decision. I drove the van with the 4BTA for 87,000 more miles. I then purchased a 1991 Ford F150 4X4 new with a 5 spd manual transmission and a 300 cid six cylinder engine. I immediately swapped out the engine. I drove the pickup for 202,000 miles, so when I finally sold the truck (to purchase 99 Dodge Cummins, of course), the 4BTA had accumulated just under 290,000 trouble free miles.

I would think that you can get some good power from the 4BTA engine with today's technology, but I don't think you could overcome the one drawback of it being only a 3.9 liter displacement engine which is considerably smaller than its 5.9 liter bigger brother. I would be especially concerned if you are going to put the 4BTA engine in a truck larger than a 1/2 ton. My concern would be that engine torque would be very limited at low rpms because of the small engine displacement. For example, on my 1991 Ford engine conversion with the 5 spd manual, I always had to get the vehicle in motion with first gear. Also, in the event of using an exhaust brake, the engine would have considerably less braking power than the 5.9 liter engine.

Whatever you decide to do, it sounds like it will be a fun project. Keep us posted.

- John

 

[DonFitzwater]

Thanks for the Cummins history lesson John. It would be nice to have something like that available today but with all the computerization and stranglehold of emissions regulation we can probably forget it.

 

[50BMG]

Thanks for the information petersonj. I had no idea that they did this and I would like to see the performance ratings of a setup like this.

 

[petersonj]

Thanks for the comments. It was a fun engine to have at the time, especially when Dodge hadn't come out with the Cummins in their trucks yet in 1988. During those times I could easily drive up Vail Pass, Fremont Pass, and up to the Eisenhower Tunnels at 65 mph in overdrive and no smoke. Back then when I was going up those mountain passes I had always wanted a sign on my tailgate that said, "You have just been passed by 3.9 liter diesel engine".

By the way I spent the first 18 years of my life in Fairbanks, Alaska. It was a great place to grow up.

- John

 

[Wayne M.]

It probably is not too well known, but back in the mid 80's Cummins offered a 4BT or a 4BTA diesel engine that would fit behind small block engines for Ford, Dodge, and Chevy pickups. The kit included a bell housing adapter and flex plate for automatic transmissions and the engine was EPA certified for all 50 states at the time. The engine could be purchased to mate with an automatic or a manual transmission.

From the 1984 to 1994 I lived in Leadville, Colorado at 10,000 feet in elevation. I drove a 48 mile round trip to work at Copper Mountain Resort (at 9,600 feet) and back, crossing over Fremont Pass (twice a day) at 11,300 feet. My primary vehicle was a 1984 Ford E150 passenger van with a 300 cubic inch in-line six cylinder engine. Naturally aspirated engines gasped for air at those elevations. I had always thought that a small turbocharged diesel engine would be a shining star in performance for this application.

So, one day in 1987, a Cummins rep was delivering a diesel engine that provided auxiliary power for a small ski lift at Copper Mountain. The engine weighed 2,500 lbs and was being delivered in the bed of a 1985 Ford F250 2WD which was powered by a 4BTA Cummins engine mated with a Ford C6 automatic transmission. After some conversation with the Cummins rep, we took the truck for a test drive up the 7% grade toward Fremont Pass with me at the wheel. I came to a complete stop with the truck about half way up the grade. Starting from a standstill I was able to get back up to 50 mph. I was impressed.

In 1988 I made a decision and purchased a 4BTA (rated 120 hp @ 2500 rpm, 315 lb/ft tq @ 1700 rpm)
engine kit from Cummins for $5,300 and I swapped it with the engine in my van which by 1988 had logged 118,000 miles. It turned out to be an excellent decision. I drove the van with the 4BTA for 87,000 more miles. I then purchased a 1991 Ford F150 4X4 new with a 5 spd manual transmission and a 300 cid six cylinder engine. I immediately swapped out the engine. I drove the pickup for 202,000 miles, so when I finally sold the truck (to purchase 99 Dodge Cummins, of course), the 4BTA had accumulated just under 290,000 trouble free miles.

I would think that you can get some good power from the 4BTA engine with today's technology, but I don't think you could overcome the one drawback of it being only a 3.9 liter displacement engine which is considerably smaller than its 5.9 liter bigger brother. I would be especially concerned if you are going to put the 4BTA engine in a truck larger than a 1/2 ton. My concern would be that engine torque would be very limited at low rpms because of the small engine displacement. For example, on my 1991 Ford engine conversion with the 5 spd manual, I always had to get the vehicle in motion with first gear. Also, in the event of using an exhaust brake, the engine would have considerably less braking power than the 5.9 liter engine.

Whatever you decide to do, it sounds like it will be a fun project. Keep us posted.

- John

THAT is the BEST (!) story I've read on here in a dogs age. Thanks.

Spending 5 intimate years with a fleet of displacement hull work boats powered by CAT 3304's running 24/6, you get to know the duty cycle difference between land and sea. Those engines gave brutal service.