96-03 400SB Engine choices

J

jmunro123

Member
Feb 2, 2008
370
Gran Bend, Great Lakes
Boat Info
2004 Sea Ray 390 Motor Yacht
Engines
8.1's
I am trying to figure out what Sea Ray was doing on the engines on this vintage. I am primarily interested in Diesel engines but notice two choices are Cummins or Cat. I would prefer Cummins. Does anyone know when they started offering Cummins or what happened here on the choice of engines?

Am I wrong in thinking the Cummins are better?
 
2001 Caterpillar & Volvo
2002 Caterpillar, Cummins & Volvo
2003 Cummins & Volvo

Diesels were options. Volvos are usually only found on boats built for export insce they are more popular in Europe.

Cummins are not better....just different. Caterpillars have more torque and are more efficient and have a little less smoke on a cold start. Cummins are a little more sensitive to overheating since their cooling systems, while adequate, do not have the extra capacity that is engineered into the Caterpillar cooling system. Caterpillar's unit injection system is expensive to produce but supremely simple and almost never causes problems, Cummins uses a more economical system to produce and it isn't as efficient, but it isn't known to cause any more or less trouble than the Cat system.

Caterpillar shipped some engines in the 1996-2000 (approx) time period that had some faulty valves. The defect didn't show up until the engines had 125-150 hours on them, so you aren't going to find any running in boats now that have not been repaired unless you see one below about 150 hours. You frequently hear that Sea Ray stopped using Cat engines because of problems with them, but that isn't the case. Mercruiser and Cummins entered into a joint marketing agreement...i.e. Cummins-Mercruiser, and Mercruiser is a Brunswick Company so Sea Ray moved to Cummins engines to keep the purchase within Brunswick.

Which one would I choose? Doesn't matter at all to me. I happen to own Caterpillars which have been trouble free....but I also own 2 Cummins engines in some non-marine equipment. All are excellent engines.

Engine choice should not be a qualifier on choosing a boat. You need to find the best boat you can in terms of condition, known maintenance history, location, etc. Then do your due diligence on the hull and engines by having a full mechanical survey of the engines, transmissions and generator and a hull survey done before purchase.
 
Frank, I've heard references to Cats having high torque before, but in the case of a 400DB, we could be comparing a 3116 to a 6CTA or a TAMD 74.

Both the Cummins and the Volvo are significantly larger in displacement than the Cat, at 8.3 and 7.4 compared to the 3116's 6.6, and have have a longer strokes as well.

Given that, could the Cats really have more torque?
 
I haven't a clue on Volvos.

I run a 460DA, a 420DA, and a 450EB, all with 6CTA's for folks in our marina when they can't get to their boats and my boat with 3116's, and the 370DA with 300 hp 3116's that Arrrgh- Arrrgh just boat both have noticably more torque than the Cummins boats. Torque is a product of more than stroke.....I suspect fuel delivery and valve timing has an effect as well.
 
I can vouch for that, I run several 460s and a couple 450s in my harbor. The 450s that I run with the 3126s have TONS more torque dockside than the 450 Cummins, getting on plane is about equal.
 
That's easier to explain. The 3126 is 7.2 liters - more comparable to the 6CTA and Volvo, and the 460 is a bigger boat than the 450.
 
No it isn't; it only adds confusion.

The power and torque curves on the 3116 and the 3126 are virtually identical up to about 1500 rpm. The added displacement on the 3126 is only useful at cruise speeds and above.
 
Frank, I looked at some torque specs. They show significantly more torque from the 3126 even at 1200 RPM....?

Back to the original inquiry, I'd say that engine choice is HUGE factor when buying a boat, and IMOH should be one of the most scrutinized aspects of the entire process.

Any nice boat (and the 400DB certainly qualifies) with the wrong engines can be an ownership nightmare. Things to be considered are how well-matched the engines are to the vessel (from fuel hog to performance slug), the quality and availability of local service, livability (vibration, noise, smoke, reliability), cost of parts, and because perception often IS reality, the reputation of the engine plays a role as well.

If you were to come across a 400DB with Volvo power (unlikely, btw), it will have depreciated beyond a Cummins powered example. The reasons have a LOT to do with perception. It's a good engine, but SeaRay owners aren't comfortable with them. This is also largely regional, so laying blanket statements like this across too wide of a region isn't wise. (in the Great Lakes, SeaRay buyers run from Volvos. If you want a good deal on some nice Swede powered boats, I could show you some examples that have been on the market for literally years)
 
Ok, so I understand you correctly, you think that a particular brand/size engine is the best choice for a boat so that is the only boat you will consider? So just because a boat does not have an "X" engine, you will not consider other nicer, better maintained boats offered for less money, in more convienent locations even though effective performance numbers are about the same and fuel economy is better?

As far as the torque question.........have you ever run similar boats, one with Caterpillar and the other with Cummins engines? I think not or we wouldn't be arguing about which has better torque.
 
I think I understand what Frank is talking bout re: apparant tourque on the 31 series Cat's
My 3176's would actually make the boat lurch when you put them in gear. Just putting htem in gear at idle would make the stern of the boat drop a good tow or three inches from the sudden forward movement. It was very nice to have that power at idle when docking in the wind with no bow thruster.

On the other hand those same engines struggled to get the boat on plane and then all of a sudden made gobs of power very quickly once the finally spooled up.

You could they they had more tourque, or you could say they had less.

To me it is all about the combination. How well, gear ratio, prop diameter, and tourque curve of the engine matches what the hull requires.

To me the only way to really know is to run the boat and see. Then factor in reliablilty, resale, etc.
 
sorry 'bout the typos in that one guys.....
I can spell. I just dont type well/fast.
 
I know exactly what you are talking about with the Cats. I know they are different boats but the 450 and the 460 in my eyes are basically the same to me. I run a 1996 450 with 3126 Cats (420 HP Version) and a 2000 460 Sundancer with 450 Cummins. The 96 450 literally squats down and gets moving a TON faster then the 2000 460 does. To me I feel like the 2000 460 barely gets out of its own way at idle speed (however that all changes getting on plane). For instance, the 460 I can leave in gear the whole way through the harbor without throwing a huge wake, the 450 needs to constantly be taken out of gear or run on one motor when idling through the harbor.

The 450 with the Cats however runs like a bat outta hell to me at all speeds and maneuvering.

I love the way Cats sound and perform however the 3196 issue scares me off of some boats, ultimately I'm buying a Cat 3196 480 Sedan Bridge in the near future if that says anything.

Alright this is way off topic, if I were buying a 400 Sedan Bridge, it would have either 3126s @ 420hp or the 430hp Cummins. Largest horsepower available is the only way to go for me!
 
If you are looking at a 480, they Cummins/Cat comparison is completely different as that boat it is either the Cummins QSM-11 or the Cat 3196. The QSM-11 is a very different engine/design than the smaller Cummins engines...
 
It sure is, I have run a few 500/52 Sedan Bridges with the QSM-11s and they are an incredible engine, its my first engine choice but the price difference isn't!
 
Geriksen- your 3176's were in a heavy boat and based on our earlier exchanges, I'm not sure there wasn't some problem with exhaust gates, pressure settings, etc that caused an extremely long turbo lag on those engines. The discussion here is about torque and you would only feel the torque in handling below the point that the turbos kick in.

Gary is right....this discussion was about the differences between 31XX series Caterpillar engines and 6CTA Cummins in a 400DB. The QSM-11 Cummins is a completely different can of worms (or bucket of bolts). I can't tell any torque difference between the QSM's and a 3196.
 
Well here's my 2cnts. I have no experience with the QSM11s, however I did sea trial a 460 with the smaller cummins engs. While it had great low end acceleration the low speed handling was simular to my 400DA gasser. In fact it may have been worse because the 7.4s are very responsive on the bottom. A little burst of throttle = a lot movement. My friends who have Meridians with small cummins had a tough time keeping up with 400DA, and didn't get much better MPG because they had to run such high RPM to keep up. My Cats are at idle when they're (Meridians) are at slow cruise. I have to warn my passengers before I put those animals in gear. The only other big blocks I have experience with are MAN 800hp engs. in a 550DA, and I don't recall it lurching when gearing up.
 
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