Gentlemen: I have read the above posts and I have to admit the knowledge is way above my pay grade. I just drive "THE TOY" at its top speed of 68 to 72 MPH as Mr. Barth intended. The speed variations are due to minor hills and tail winds.I am guilty of mashing the throttle, otherwise the Volkswagen stopped behind me at the traffic light will have to push me move my 160 HP Cummins.....................

"Mashing" the throttle: When I mentioned "feathering, I mean not to stomp the accelerator. Let the turbo spool up. Stomp it and you get more diesel fuel than the engine can efficiently burn, and this scavenges lube from the cylinder walls and leads to engine deposits. I generally take about 3-4 seconds to apply full throttle from a standing start, but try to avoid that whenever possible. As someone else on the forum has said, "Diesel coaches do not accelerate - they 'gather momentum'".

"Lugging" any internal-combustion engine is inadvisable; it can drive BMEP off the chart. Mashing the throttle can have similiar results.

The optimum cruising RPM for an engine is within 100 RPM of peak torque. On mine, peak is 2,600, and I run at 2,500 (in 3rd, because in OD it's 2,200). I would guess that with the C5.9L, it's about 1,800-1,900.

The C5.9L at 160 or 190HP is probably "breathing limited", meaning that at full throttle, it's limited by fuel and air supply from producing more power. The uprating of that engine involves providing more fuel, more air, and/or cooling the air after the turbo.

Rusty: Are you stating I would do better in 3rd gear as opposed to cruising in 4th gear? Thanxx

Rusty, on the Cummins there is a pressure operated fuel control on the "P" injector pump, "mashing the throttle" will not over fuel the engine at low speeds unless it is adjusted out of factory calibration or larger injectors have been installed. It would really smoke if that were the case! Right Gary?? I can't get anywhere close to full boost (20 PSI) unless I floor the pedal.

Carl, you would not get over 51 MPH if you drove in 3rd. and that would be at 2800 RPM. NOT advisable, you are going away from peak torque, but you are stuck because with the 4 speed there is a compromise between acceleration and top speed. Run just as always but remember, don't lug the engine, as soon as the speed drops under load, (like up a grade) shift to a lower gear and keep the engine RPM as high as you can. These are the theoretical shift points for your engine, transmission, rear end ratio, and tire combination

1st=20.6 MPH
2nd=31.8 MPH
3rd=50.7 MPH
4th=71.4 MPH

The above is the maximum speeds calculated by the tire size and gearing. So if you were approaching a hill and your speed dropped below 50 MPH in 4th (full throttle), shift to 3rd and continue up the grade, if the speed still decreased, and you get to 31, shift into 2nd and so on. Again these are calculations and your actual observed speed/RPM may be different as tachs and speedometers are not that accurate. You could verify what the top of the governor speeds are by just drive to the MAX RPM in each gear and recording it for your future reference.

My peak torque is at 1500 -1700 or so RPM BUT I run all day long at 2000-2100 RPM in 6th which is 0.65:1 O/D.

Somewhere I read peak torque is 1400rpm on the 5.9. I do know my engine does not like rpms over 2000 but will pull like crazy between 1400 and 1900.

And I can make lots of smoke if I don't let the turbo spool up. So I take off like I have a marshmello on the pedal and wait for about 10 lbs of boost before pedal to the metal.

In my case 5th gear is really a freeway gear and didn't work out to well in Newfoundland. I think the road designers were smoking something when they laid them out.

I do need to find someone who can set the pump up correctly.

Just checked with friend at Cummins and they rate the 12V 5.9L peak torque at 1600 RPM.

Mine will pull hard to 2300-2400 RPM, and after there is a noticeable drop in power to TOG (2800 RPM). The automatic shift points of the Allison is set to 2400 RPM at full throttle.

Gary will you be back in Yuma near the end of October?

Running at RPM higher than peak torque doesn't cause problems; it's just a (very) general rule-of-thumb that best efficiency is there.

Like Gary, I treat the throttle delicately until I get about 4 psi boost. Stall speed on the new torque converter is set low; before I didn't have to go slowly because the engine could wind up first.