Repowering a 1999 370EC

J

JBJ

Member
Jan 14, 2008
111
Solomons MD
Boat Info
370 EC 1999
Engines
Cummins 6.7 QSB 480 hp
We have decided to repower our 370EC with Cummins 5.9 370hp engines, it currently has 7.4 Mercruisers in it. I know economically this makes no sense.:smt021 But my wife and I love the boat and decided that this year or next would be a good time to do this project. I was trying to figure out what performance I should be able to get from this package, I figure that it should be similar to the Cat 3116. Also we are getting a 7.5kw Onan quiet diesel generator. Anyone have any opinnions on what kind of performance I can expect? I know a Luhrs 36 sportfish that cruises at 37mph at 1 mpg with the same engine.
 
Top speed won't be that of the Luhrs because it is a much lighter boat. The B Series Cumins have a lot less torque than the 3116 Cat so handling in tight quarters isn't going to be as good nor is mid range power. Top end may be about the same as 300hp version Cats. This is usually more than just an engine swap. You've already figured on the generator, but you will also probably need new shafts, props, rudders, transmissions, gauge senders, engine beds, and fuel system. The last time I saw the numbers added up was for new Cummins 6BTA's in a 390Ec and it totaled more then $85K.
 
Looking at the specs for the Cat 3116 350hp the Cummins has 40lbs. less torque at mid rane but at 2400 rpms is about equal to the Cats.(if I recall correctly) The luhrs sportfish is listed at 18,000 lbs the same as SeaRay says for the 370EC. The quote I received was $82,000 for everything.
I appreciate your input!!!!:smt038
 
Make sure you take lots of pictures....it sounds like a great project.

-John
 
For the Luhrs I meant to type that it cruises at 27mph!!! (not 37)
 
I did a similiar conversion a few years back on my 99 400 EC. She had 380 HP Horizons. I can tell you after 500 hours with NO issues it was a great choice. With the gas engines I cruised at 23 knots, burned 32 gph. With the 370HP Cummins 6BTA cruise speed is now 24 knots burning 20 gph. Frank is a big Cat guy but 2 things to consider here. Going from the gas engines the torque with the Cummins is amazing. I don't think the Cats torque is much different as I ran a 400EC with 3116's. The Cats are very noisy too. One reason is the turbos are in front of the engine opposed to the rear on the Cummins. It makes a huge difference in the EC as the engines are under the helm seats facing forward. If you need any info don't hesitate to reach out to me.
 
What a great project... can't wait to see your progress... good luck

Jason
 
The Caterpillar noise was most likely turbo squeal. From 1995 thru about 1997, Cats were installed in Sea Rays without Walker AirSeps. The AirSep does a great job in controlling intake noise and without them, Cat 3116/3126 engines are deafening in an EC or DA style boat. Sea Ray had the Cat marinizer install them on all engines after about 1997. In my opinion, if the AirSep isn't standard equipment on your new engines (and they may be), you should spend the money and add them at installation. In addition to intake noise, they control crankcase fumes and mist in the engine room. Your boat will be a lot easier to keep clean and more fun to work on if you don't have to deal with crankcase mist.

My comment about torque was about low end to mid range torque.......to see the difference you will actually feel running the boat, look at the torque curves under 1000 rpm. The further up in the rpm range you get, the less noticeable difference you will see and feel between 300hp Cats and 300hp Cummins. At cruise speeds, I can't tell any difference between them.
 
Al- How is the noise level compared to the gas engines? I take it that you have the mechanical injection Cummins. May I ask what generator do you have?

Frank- I appreciate your technical expertise, I never thought about the Air Seperators.
 
The noise level is considerably less than the gas engines at cruise. Some of that is because of the cruise rpm. 2300 vs the 3400 with gas. I have a Kohler 8EODZ gen. If you would like to see my boat and I would take you for a ride let me know. We aren't that far away as my boat is in Baltimore.
 
Thanks Al, the next few weeks I am busy but I may take you up on that!
How is it at idle noise and vibration wise?

The boat came with 8.3 6CTA Cummins as an option - has anyone been on one with this powerplant?
 
Yes.............the 430 hp Cummins C's are almost a perfect match for this hull/weight/balance boat. Intrestingly enough, the boat I ran happend to have been repowered from Merc's to 6CTA's. I found the engines to be quiet and smooth......they had 1800 hours on them when I ran the boat. They have about the same torque as Cat engines but more power in the upper ranges, so they will burn a little more fuel if you run them at high speeds. They are nearly bullet proof engines, and this isn't a Cat-Cummins debate, but the only negative I can find is that the Cummins cooling systems require more regular maintenance, but at least you can get to the engine son the 370EC.

JBJ said:
Thanks Al, the next few weeks I am busy but I may take you up on that!
How is it at idle noise and vibration wise?

The boat came with 8.3 6CTA Cummins as an option - has anyone been on one with this powerplant?
Click to expand...
 
Carey's Diesel in Delaware provided the engines and facility. I did 99% of the install myself. I would highly recommend them for any refit.
 
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