Kevin Rutherfrauds $200000 Signature glider truck has complete engine failure!!!

This is exactly right. The newer ones aren'tmuch better. 1300 is about the bottom of the power band. for four cruising along, but you better get it up to 1450 before beginning any climb

 

Well, let's see what the "corporate" guys say about their Series 60. See the attached DDEC Brochure PDF. They suggest spec gearing so that 1400 is the MINIMUM for whatever speed you are gearing for from 60 mph on down. For above 60, the RPM recommendation increases. So, "corporate" seems to be on a same wave length as BM. Seems some here are not up to speed on what "corporate" recommends for the Series 60 12.7 and 14.

The fallacy is assuming the point at which peak torque is reached is also the point best fuel economy is reached. Let's take a look even further at the DD15. Peak torque is reached at 1100 RPM. Many folks gear the trucks to run down around 1200-1300 for some idea of maximum fuel economy. Now we fast forward to Henry Albert. Most folks have heard or read about him. He is the Master as fuel economy. He got just shy of 10 mpg on a CA to NC trip with a gross of 76,000 lb in a Cascadia with a DD15. I talked with him about what RPM's he ran the truck at, and he stated that he was running 1375 - 1425 for the entire trip. Here we go again. 1400 or more for maximum fuel economy.

So, not so sure that BM is all that far off. In everyone's rush to criticize him, might be best to do a little research. In other words, put your brain into gear before engaging you mouth.

 

It is generic advice and it is the reason why automatics are getting better mpg than fleet drivers shifting manually.

You should look up (or create) a BSFC map showing fuel consumed vs power made throughout the rpm range for your engine:



Then you monitor your horsepower output (with scangauge, bully dog, etc) and shift to be in the appropriate rpm for your power. This will mean frequent shifting and you will probably cruise on flat ground at a much lower rpm than with a hill or wind.

The Detroit recommendations:


...just use a generic power graph:


That graph says that at 55mph, I should be using ~160 horsepower, but my truck is much more efficient and actually uses ~80 horsepower to cruise at 55.

At 80hp, 1200 rpm is 3% more efficient than 1400rpm (BSFC of 0.35 vs 0.36).

Now if I was just handing the keys to a driver, I wouldn't say run at 1200rpm because they'd just set cruise control and wear out the engine lugging up hills. But for someone closely monitoring their gauges/driving there are gains to be made...

 

All great info. One thing I would like to see from the OEM's is also a gallon per hour consumption rate graph included with the HP and Torque graphs that is current with each motor. Last one I have seen for a heavy diesel was for a 1996 N-14 I had. That one, and the data from 1994 you show. I did also manage to scrape one up for my 2006 Jeep Liberty Diesel, but it took some serious digging. In that case, the EPA highway mpg was 27 and using the data from the HP/Torque/GPH graph, I could consistently get over 32 mpg highway.

That being said, while one does only need the amount of HP to move a load, determining at what RPM that will deliver that power most efficiently is the crux of the issue. While I may only need, say, 200 HP, and I can get that at a lower RPM, I can also get it at a higher RPM. Now how efficiently each RPM range delivers the power I need is the key question. Back to the Cummins N-14 graphs I had, the most efficient, i.e. lowest GPH rate was between 1350 and 1500 RPM. The curve started out higher, dropped down as the RPM's increased, leveled off, then as the RPM's increased further, the GPH line went back up and climbed. So there was an efficient RPM range that would deliver optimum fuel efficiency. And it is not directly equal with the torque or HP curves. They are all independent.

So, in a nutshell, I may get that 200 HP (in the max torque band) at a, say 1200 RPM on a motor, I can also get that same 200 HP at a higher RPM. Just because the curve shows, say 400 HP at 1400 does not mean that it is delivering that. Those numbers on the graph are maximum HP at a given RPM, non minimum. One can be coasting down a hill at 1500 RPM, and the motor is not delivering 500 HP at that point, as no fuel is being applied to generate power. It is quite feasible, that I could get 200 HP more efficiently at a a higher RPM than at a lower RPM. That is dependent on the engine.

A Detroit 60 will not have the same fuel consumption curve as a N-14, or an ISX, or a Cat C-15, or a DD15. And neither of those motors will have compatible fuel consumption curves as the others.

There are many things that can affect this. Rotational inertia of the motor could have a parasitic effect at a lower RPM. So while a given RPM can deliver a designated HP, it is also having to work harder to do so than at a higher RPM. That is where a fuel consumption graph can show factors like that.

See the attached PDF. It is a brochure on the motors from the OEM than made the diesel in my Jeep. Notice the power charts. They show HP, Torque and Fuel consumption graph lines. Notice how the fuel consumption is higher at low RPM, drops down to the most efficient level, and then starts to climb again. this is what I want from our heavy diesel OEM's, but it seems like pulling teeth to get it.

 

I see this thread is still running has more miles than the truck.

 

I agree Kevin Screwyouford is slighted on his views. I sometimes have wondered if Detroit and others pay for his commentary. Not saying that a Detroit motor can't get good MPG, but what you have to sacrifice to get it does not make it the best choice on the market. Unless you enjoy having engines overhauled on a regular basis.

 

Define "regular basis".

 

600K - 800K. Although I have friends that have over 1M on some of theirs, so it may be that most that I have seen were abused as a fleet truck prior. I have owned a few and found that they were pretty decent on fuel if driven properly. In comparison to my Volvo D12s that I have never overhauled and they all have over 1.2 M on them. The drivers have not given them any mercy, and they still average between 8 - 9 mpg when I take them out. But I can get between 6.5 - 7.2 with a cat as well.

That has just been my personal observation. Series 60 12.7 is a good engine if taken care of.

 

Oh yeah, I have two N14's as well each with 1.3M and 1.5M on them forgot those get between 6.2 - 7.2 mpg

 

Wait a second. First you say Detroit's have to be rebuilt on a regular basis, and then you say it's a good engine if taken care of.

So which is it hillary?