Is it possible to lug a truck at peek RPM?

Just thinking if the engine will maintain speed, what's the problem? It's working harder on uphill pulls, which means more fuel and a deeper exhaust sound - maybe that's what you're hearing?

 

Normal, you are just hearing the engine working harder. Lugging isn't until it is down to 1000 rpm.

 

This is where a pyrometer and boost gauge come in handy. While the spec sheets show peak RPM at 1000, it is usually not advisable, even by the OEM, to run full power on a hard pull for more than a few seconds at that low of a RPM, or even 1100. Exhaust temps at those low RPM's could easily climb to too high of levels than are prudent. At that point, the engine is fighting with itself and an excessive amount of heat is being generated. There is a balance, and each engine is a little different. If I still had a lot of hill to pull, I would keep RPM's above 1300. I have let ISX's go on down lower, but I was about ready to crest the hill and I knew that it would not be running that low for more than a few seconds. To the OP, there is really no way any ISX should be even close to "lugging" at 1400-1500 rpm.

 

If your keeping it in the "sweet spot" then I wouldn't call it lugging....

 

First we need to define "lug" - "To carry or drag with great effort".

There is no specific rpm which defines lug. It is when the engine is working at an inefficient rpm to capably do it's work when a gear change to a higher rpm would be more efficient.

Unless you have a pyrometer and boost gauge you are just guessing by sound and feel.

 

Yep there is.....my Mack says do not run under 1200rpm....the old Mack is not under 1400.....both values are the start of the max torque curve (straight line) of the individual motors.....

Keep it in the operating range (or torque curve if you have access to a power graph) and you should be good....

 

I have lugged an ISX15 back all the way to 900 rpm multiple times without any problems. I don't advise going down to 900 but you would want to shift to a lower gear by 1000 rpm. Lugging the ISX down to 1000 rpm (2010 and newer) won't hurt it at all. I haven't ruined an engine by doing that yet and I will run it down to that RPM for as long as I can because of the gear down protection and load based speed control that they have on the trucks now. I believe that the 2013 ISX has full torque all the way down to 1000 rpm.