Detroit Diesel Fuel Consumption ... yes another thread

[richardoren]

DDs are great, and shouldn't be repowered to puny overstressed 4-strokes unless you have a need for speed or will be covering big distances and don't mind more frequent majors.

But, over in the boatdiesel forum, folks are saying that there is up to a 30% difference in Brake Specific Fuel Consumption between a DD and a modern 4-stroke diesel. Others there say that it is due to the DD's blower which is a parasitic load that can't get gotten around, and which other engines do not have. This is without mentioning the greater weight of a hefty screamer to move onto plane.

While some of this makes sense, I was wondering if that isn't a way exagerate estimate of the blower's load?

How much of this can be attributable to modern engine management systems, and those of the most recent generation 92Ti series is said to be good, can they be plugged into an old N/A DD? Or are they those things that shut down your engine every chance they get?

Just musin'

[MikeP]

Well, there's no doubt that modern computer-controlled engines of any kind are considerably more efficient overall than older ones and 2 strokes have always been noticeably less efficient than 4 strokes. Put that all together and I wouldn't think that the 30% figure is out of line.

There is some drag associated with the blower - as there is with any piece of equipment that the engine must turn but the major difference is simpy due to the mechanically-injected 2 stroke's limitations compared to the electronic controlled modern 4-stroke.

But don't those old DD's sound GREAT?

[richardoren]

Hi Mike,

I guess I didn't realize that this "blower" was actually a mechanical fuel injection. I'm all sold ever since my old mechanical injection vintage Benz which sure sounded addictive. As for the DD sound, I'll tell you after Sea Trial on Tuesday. These are the screamers - highest compression ever small sized high pitch screamers: 8V53s. They probably sound way different from 92s.

Regarding the sound, I'll probably like (love) it, but for the Admiralty I'm thinking of looking into cheap and simple measures. Some use lead barriers under the salon floor, others prefer Ensolite foam insulation. And there are those who reported success in adding Salisbury Hydro-Vac exhaust silencers to their boat - they are heat resistant neoprene or marine fiberglass elbows that attach over the exhaust outlet and redirect exhaust and noise under the surface:





Anybody here ever used these?!? Could be nice with marina neighbors that hate smoke & noise.

Otherwise there's always Don Hayward's schematic for quietening Detroits by installing a muffler immediately downstream of the exhaust manifold and upstream of the water injection.

Seems like it might be worth a shot, unless it can compromise airflow to the engine which depends a lot on the relatively open exhaust of a two stroke?

Or just tell 'em to love the noise or walk the plank!

[Boss Lady]

the new four strokes are more efficient for many reasons, lower internal drag from newer bearing types, rings and other components, the use of lower viscosity oils and synthetics, a four stroke does not use mechanical fuel injectors run off the cam lobes, no blower drag, which is substantial, and a complex fuel delivery strategy, which allows for a more efficient burn, and last but not least, the computer more accurately matches the fuel flow to the demand and boost pressures. Detroits are strictly mechanical affairs. The computer engines make adjustments on the fly, where things are mechanically set on the Detriots.

[REBrueckner]

I'd agree with the comments above...30% is likely in the ball park. On the other hand, I really doubt most of that improvement is due to the blower itself....there have been so many engine efficiency changes over the years that thinking all the improvement comes from elimination of the blower doesn't make sense. Maybe 5% for the blower would seem reasonable, and 10% would begin to stretch my belief without supporting factual design/test data.