i have to admit i don't own a cummins yet but i was wondering what the issue with lugging is on a diesel. A gas motor starts pinging if u lug it too hard but i always figured that was imposible on a cummins so whats bad about lugging?

 

Oil film on the bearings is not suspended very well at low speed . . . huge main bearing diameter helps with that.

The injection timing is set at anywhere from 13°-2X° BTDC and the low rotational velocity causes the cylinder pressure to spike before the piston is at TDC causing the piston to push into huge pressure, more stress on everything.

I've been called away form the computer . . .

Take care,
Phill

 

To add to the above....

On a five speed tranny lugging in overdrive (5th gear) has been known to loosen the nut that holds the gear in place. It will eventually cause it to move out of place and cause 5th gear failure. They sell an updated nut that is suppose to help prevent this from happening. FYI

 

well i personally do lug my motor i have a 97 12v and a torque converter lock up switch and at 40 mph i flip my switch and lock my torque converter and then i slow down to 30mph still in 4th gear and lay into and my truck smokes pretty good. i see nothing too bad about it. and my dad has a 5spd that i also lug to make roll coal but not in 5th tho.

 

Also, not enough oil pressure to put enough oil up to the top end of the motor under that much load...thats what ive always been told.

 

There really isnt anything major wrong with that as long as your no pulling a heavy load or as long as your not doing it every single time you pull out. Not only does it add stress but if your are heavily fueled, your washing your cyls out.

 

By running lower rpms, you are getting more power out of each revolution which puts more stress on things. Part of the problem is that ignition may start before the motor has reached tdc which really stresses everything. If you downshift one gear, you may be putting the same amount of fuel into the engine but each combustion event will have less fuel since there are more events.

There is no advantage to lugging unless you like to produce lots of smoke. Contrary to what a lot of people think, lugging does not produce good fuel mileage. The more power you need from your engine, the higher rpms you should run.

 

what do u guys consider lugging? 1350 and below or so? Im usually at 1750-2000 all the time, i'd like to be at 1550-1750 all the time.

 

Lugging is a function of rpm and load not just rpm. When you idle an engine, you are not lugging it but you also have no load. As the load goes up, the rpm must go up. Since wind resistance is increasing approximately proportional to the square of the velocity, the faster you go, the higher rpms you need to run assuming relatively level ground and constant speed.

If you have an egt gauge, lugging will produce high temps. For example, if I drive 45mph in 5th(3.55 rear) which is 1400 rpm, my egt's are 750, but if I shift to 4th with the rpms at 1800, my egts drop to 550. The reason that the egts are lower is that you are running more lean.

I think the best way to treat lugging is to drive for the best fuel economy. The best fuel economy will not be produced when lugging but it will also not be produced with excessive rpms.

Sorry for the long answer but I don't know of any straightforward answer. The problem is that lugging is a function of both the load and the rpms.

 

ok so, mileage aside the main problems are ignition before tdc and low oil pres.

from what i know if you retard the timing that solves the ignition before tdc problem(correct me if im wrong) but what about the oil pres. is it much of a problem?

 

Lugging is very hard on your torque converter and automatic transmission. There's too much torque and not enough pressure built up in your trans to hold the power at low RPM's.

 

Also the pulsing to the driveline, especially the transmission. As was said before, each pulse is doing more work, thereby putting more stress on each tooth and ball bearing of the tranny. (mostly manual). When it wound up higher, the work is divided more evenly among the teeth and ***** within the transmission.

If you ever listen closely to a trans that's a little loose (older) when it's lugged, it sounds a heck of a lot worse than when it's running at a little higher rpm.

Take care,
Phill

 

yah towing i don't lug the motor at all and in my truck that thing slips all the time when i lock the torque converter, i lug that thing a lot for example if i want my truck to smoke i slow down to 30mph in 4th gear with it lock down to 1000rpm' and lay into it and roll some coal but i don't do that too often.

 

Why not just avoid lugging the engine?

 

Lugging the engine is when you are getting the same amount of fuel and not enough air therefore the EGT will spike if you do it very long you will be replacing the pistons. Rule of thumb if you mash the throttle and do not gain RPM DOWNSHIFT