Differences in diesels

scooper321

scooper321

Well-Known Member
Jul 4, 2015
1,863
Baltimore, MD
Boat Info
2003 Sea Ray 400DB
Engines
Twin Cummins 6CTA-8.3
So I was browsing boats today and came across a 390DA with Cummings QSB5.9 engines. And then I saw a 420DA with Cummins 6CTA 8.3's. Both boats are 2005's.

I'm used to seeing the CTA's in other boats (older sedan bridges) but I know nothing about the QSB. Is it a newer engine? Does it replace the CTA's in some sizes? Or is it a smaller engine? I can't find a comparison on line anywhere. Can someone give me a brief summary of the differences?

Thanks,
Steve


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In the medium sized Cummins engines, there has aways been a "B" series which is a 5.9L engine and a "C" series which is an 8.3L engine.......2 completely different engines. The 6 in the model name just means the engine has 6 cylinders; the B or C indicates the engine family, the T means the engine is turbocharged; the A means that the engine is aftercooled. As more modern technology has crept into marine engines, Cummins changed the model designations. The QSB engine is based on the old 5.9L design, and the QSC is based on the old 8.3L block design. Both QSB and QSC are electronic common rail engines.

To put things more in perspective, the smaller displacement engine started it marine life as a 6BTA and was rated at 300 hp, the 6CTA started at 430hp. Now the QSB is up to 500 hp; the QSC is up to 600 hp.
 
fwebster said:
To put things more in perspective, the smaller displacement engine started it marine life as a 6BTA and was rated at 300 hp, the 6CTA started at 430hp. Now the QSB is up to 500 hp; the QSC is up to 600 hp.
Click to expand...

Frank, are you saying that these horsepower jumps have been made using the same basic blocks? They're pretty significant. What technology would you attribute such big gains to?
 
Diesel engines are really pretty simple creatures. To get horepower, you have to burn fuel. A gallon of diesel fuel has only so many BTU's of energy in it. Therefore, for an engine maker to get more power out of an existing engine design, they have to put more fuel thru the engine. To do that requires one or more of the following: larger displacement, dumping more fuel into the engine via different injectors, a different fuel pump to get higher fuel pressures, turning the engine at higher rpms, or using smarter technology to control the fuel system's timing. Cummins has done all of the above gradually as hp ratings have increased. The latest engines, the Q-series use very high pressure fuel pumps, common rails and electronic injectors controlled by the ECM to get very precise timing for opening, closing and duration of the fuel charge.

I don't know precisely what Cummins has changed to the rotating assembly of the old engine designs to get the HP and rpms they deliver now, but it is a fair assumption that the crankshaft, rods and piston have been modified to withstand the rpms they turn now.
 
fwebster said:
In the medium sized Cummins engines, there has aways been a "B" series which is a 5.9L engine and a "C" series which is an 8.3L engine.......2 completely different engines. The 6 in the model name just means the engine has 6 cylinders; the B or C indicates the engine family, the T means the engine is turbocharged; the A means that the engine is aftercooled. As more modern technology has crept into marine engines, Cummins changed the model designations. The QSB engine is based on the old 5.9L design, and the QSC is based on the old 8.3L block design. Both QSB and QSC are electronic common rail engines.

To put things more in perspective, the smaller displacement engine started it marine life as a 6BTA and was rated at 300 hp, the 6CTA started at 430hp. Now the QSB is up to 500 hp; the QSC is up to 600 hp.
Click to expand...

Frank,

Thanks. This is actually exactly the sort of overview that I was looking for. I know little about the diesels, so this gets me at least a basic idea of what I'm looking at. Now I can dive into the docs and web sites the others provided. Thanks to all.
 
Alegria said:
Lol! I see I've done my job well. Good luck on the hunt!

Sent from my XT1575 using Tapatalk
Click to expand...

Ha ha. You did great. I'm not moving off my 320 any time soon. Just learning!


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