Lugging the Cummins engine

[WWalters]

After visiting the DodgeRam.org website, ( Diesel Engine Operation FAQ), I'm confused about a couple of statements that I read. Listed below is a question and answer from the FAQ's:



Q: Can I lug my Cummins engine?



From: Josh Berman <j. e. berman@metc. cummins.com>

Subject: Operating below torque peak RPM



The Cummins B-Series O&M (Operation & Maintenance) Manual says:



"Cummins engines are designed to operate successfully at FULL THROTTLE under transient conditions down to peak torque engine speed (RPM). This is consistent with recommended driving practices for good fuel economy. Excessive FULL THROTTLE operation below peak torque RPM (peak torque RPM varies from 1,100 RPM to 1,600 RPM, depending on rated engine speed) will shorten engine life to overhaul, can cause serious engine damage, and is considered engine abuse. "



So you're right, we don't recommend FULL THROTTLE operation below peak torque RPM. However, just after the first caution, the manual says:



"Operation of the engine below peak torque RPM can occur during gear shifting due to the difference of ratios between transmission gears, but engine operation must not be sustained more than 1 minute at FULL THROTTLE below peak torque RPM. "



So basically you've got 60 seconds of continuous FULL THROTTLE operation below torque peak RPM; if the engine can't handle the load and RPMs don't increase to above peak torque RPM, downshift to raise engine speed.



However, operation of the engine at less than FULL THROTTLE at speeds below torque peak RPM is ABSOLUTELY OK.



I hope this helps clarify the issue,



-Josh Berman



End of Quote



Under the 2001 Ram Engine Specs on the same web site, peak torque for the ETC engine is 460 lb-ft ( from 1600 to 2700 rpm). What is confusing to me is that in the lug engine FAQ shown above, peak torque RPM varies from 1,100 RPM to 1,600 RPM depending on rated engine speed. I guess that I must be missing the boat somewhere. Can anyone help me to understand this " peak torque" concept. I'm new to the Cummins Diesel and still trying to break the engine in right. Thanks.

 

[Bob Wagner]

the sweet zone

is 1800 -2100 RPM



Search the archives for topic deatails

 

[Steve M]

My two 12v motors had peak torque values at 1600rpm. My 24v motor's peak torque is at 1400rpm. Peak hp was at 2500rpm for the '95, 2600rpm for the '98 12v and 2700rpm for the '01 24v. We can run full throttle from rated peak torque rpm to peak hp rpm. We might be at peak torque at 1400rpm but, we don't have enough hp to do alot of work and we'll generally downshift as needed to get more hp to go with the torque. I do alot of empty cruising at 1100rpm with the throttle at almost idle position. This is definatley not lugging the engine. We can run full throttle at the engines rated speed located on the data tag for as long as our butts can take it.

 

[Missouri Mule]

Cummins has a lug protector on the fueling system. If you have ever taken foot of go pedal at low rpms/speed you would have noticed that the rpm will not drop below 800 rpm(and trucks keeps going) .

Lugging is harmful in the upper gears which are made for traveling the lower gears are power gears( to get you going ) they wind the rpm up pretty quick.

Peak torque range is aprox max torque. Max rpm in 12 valves(p7100 pump) is 1600 rpm but the peak range is a little wider.

The peak torque range is wider on the 24 valves because of the electronic injection pump (it is also flatter instead of curved as shown on a graph).

The Cummins manual he is using is not exactly just for Dodge applications but for a wide range of use for the B/ISB 5. 9 engine. Such as a tractor(farm) max peak could be 1,100 rpm the max rpm could be 2500 rpm( the rated engine speed) with the max horse power somewhere in between. In the 12 valve for Dodges max hp is 2600 they red line at 3000 but 3400 or 3600 is recommend max rpm the 24 valve are a little higher.

 

[Dave Fritz]

WWalters,



Josh Berman's comment "peak torque RPM varies from 1,100 RPM to 1,600 RPM depending on rated engine speed" was a generic statement for all Cummins engine series. The torque peak on the B occurs at around 1600 rpm. Some of the larger engines have a torque peak at 1100 rpm, produce rated power at 1800 rpm, and have a max (governed) speed of 1950 rpm. I have modified that part of the page because it appears to be somewhat confusing.



Generally, you can cruise around town in the Ram at 1100 rpm with no trouble, but you should avoid using much throttle at such low engine speeds. Also, the NV4500 5th gear nut will loosen if you do much driving at engine speeds below 1600 rpm and heavy throttle below about 1800 rpm really pounds on the nut.



Dave

 

[Doubleclutch]

Sounds like a pretty good argument for EGT and Boost gauges! Lugging the engine with a foot full of throttle will definately show up on the EGT! While driving into a headwind with trailer in tow, I know I can be "in the torque band" but have exhaust temperatures over the top. This is with enhanced fueling but I'm pretty sure the same applies to stock. Comments?