so stealing the graph from this thread. click why wouldnt running at 2200 RPM work well?

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1982 300CD Turbo (Otis, "ups & downs") parts for sale
2003 TJ with Hemi (to go anywhere, quickly) sold
2001 Excursion Powerstroke (to go dependably)
1970 Mustang 428SCJ (to go fast)
1962 Corvette LS1 (to go in style)
2001 Schwinn Grape Krate 10spd (if all else fails)

Really? And this is with your existing 617 turbo engine??

Actually if you had more experience with diesels over the road instead of in the books, you'd understand that trucks consistently deliver roughly the same fuel mileage pretty much regardless of weight of their load - or "horsepower required" as you put it. Except for dead heading empty there's very little variation at all. In fact wind direction probly carries the greatest influence. And what is this "horsepower required" factor you've cooked up? Does this measure amount of fuel we feed per horse per mile?

Yeah sure, I'll believe the 4cyl 240D w/ 616 engine is actually drivable *at any speed* with 2.47 final drive when seeing one on the road.

I just hope everybody realizes that MB 617 and 616 engines (or any diesels for that matter) are NOT gasoline engines susceptible to fuel economy fluctuations up to 10mpg. Perhaps fuel economy threads oughta be banished alongside oil and fuel price threads as being among the most worthless. I wont touch another one again, too many creative misconceptions bein passed around.

yes through 2 tanks

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1982 300CD Turbo (Otis, "ups & downs") parts for sale
2003 TJ with Hemi (to go anywhere, quickly) sold
2001 Excursion Powerstroke (to go dependably)
1970 Mustang 428SCJ (to go fast)
1962 Corvette LS1 (to go in style)
2001 Schwinn Grape Krate 10spd (if all else fails)

Look at the graph again. An OM617 cannot make 7psi of boost at 2200rpm unless you have custom mounted a VNT turbo.

Idle time probably affects it the most. A semi-truck with a decent driver can make a great 6.5mpg average hauling it's 80,000lb butt around the country. However, a few hours of idle time can easily drag that down to 5mpg or less.

i tried to decifer but not knowing normal makes these tougher to read, but that said, isnt the paek torque going to be similar with a normal 300d turbo as well?

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1982 300CD Turbo (Otis, "ups & downs") parts for sale
2003 TJ with Hemi (to go anywhere, quickly) sold
2001 Excursion Powerstroke (to go dependably)
1970 Mustang 428SCJ (to go fast)
1962 Corvette LS1 (to go in style)
2001 Schwinn Grape Krate 10spd (if all else fails)

Off the top of my head I think it is around 2400-2500 rpm

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Thanx,
Alberta Luthier
1983 300CD ('Stinky')155k miles, 2.47 diff, EGR removed, AAZ injectors with 265 nozzles from Sean,and vogtland lowering springs.
1984 300SD ('Old Blue')150k Klicks from Japan originally, came with rear head rests, no sunroof and never had an EGR

No. My peak torque is so low because I have the necessary air (boost pressure) available. A 617 won't hit its torque peak with the stock T3 or K26 turbo until around 2500rpm. The only way to lower the TP, and get boost at that low an RPM, would be to run it up to 2500-3000rpm and lug the engine down to keep the turbo active. Any automatic in proper tune will downshift well before that can happen.

For an example of a performance map of the type I was mentioning, see slide 37 of;

https://me.queensu.ca/courses/MECH435/notes/Engine_Performance.ppt

The contours are lines of equal brake specific fuel consumption, and for best efficiency, you need to be at "the centre of the onion"

No. They do have that skipshift crap where in town you are forced to shift from 1st to 4th unless you give it a lot of throttle.

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1985 CA 300D Turbo , 213K mi

I should have noted that I am running my stock auto trany with the 2.47 diff. This works great for me but the 600 rpm or so slip in the torque converter makes for higher rpms than a manual trany would with a 2.47 diff. I am not sure if a 617 would pull a 123 with a 2.47 diff and a manual trany and I am unwilling to find,buy and swap one to find out; but I am certainly interested to hear if someone else is gonna.

__________________
Thanx,
Alberta Luthier
1983 300CD ('Stinky')155k miles, 2.47 diff, EGR removed, AAZ injectors with 265 nozzles from Sean,and vogtland lowering springs.
1984 300SD ('Old Blue')150k Klicks from Japan originally, came with rear head rests, no sunroof and never had an EGR

ok, but since mine is a manual, and I would have spun the turbo up on the previous gear, would it hold the turbo speed for the 5th gear 2200 rpm cruise?

__________________

1982 300CD Turbo (Otis, "ups & downs") parts for sale
2003 TJ with Hemi (to go anywhere, quickly) sold
2001 Excursion Powerstroke (to go dependably)
1970 Mustang 428SCJ (to go fast)
1962 Corvette LS1 (to go in style)
2001 Schwinn Grape Krate 10spd (if all else fails)

There's a perfectly good engineering explanation for the relatively constant fuel economy of an over the road truck. Most of the energy to keep the truck moving is used to push it through the air...........and there is a specific horsepower required to do this...........independent of the load on the truck. The engine is very closely matched to this required horsepower and there is no possibility of getting more fuel efficiency without better aerodynamics.

Contast this with most passenger vehicles that have plenty of available horsepower by simply pressing on the accelerator. Give up that capability, and you'll achieve better economy because of it.

But, I really don't expect you to grasp any of the above...........it's way beyond your capabilites.

You've conclusively proven to all folks on the thread that your beliefs are diametrically in opposition to any engineering principles. Don't change now.

LutzTD I think your best avail. combo would be a 601 2.2 4cyl with the 5spd from a 190D. They are known to get in the 40s for mpg so adding 1000lbs should only drop you 10-15%.

Not sure. GM is getting pretty good with that system though, it actualy works pretty well.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200