So my question is, what's harder on the Cummins, a constant rpm of say 2000 to 2200, or lugging it down below 1500? Most of my driving is done between 45 to 55 mph, and with the 35" tires and the 3:55 gears I can either run it with the over drive off and run around 2k or a little higher. Or run it with the overdrive on/convertor locked up and lug around at 15k or a little lower. (these rpm #'s are approximate of course) I've read of oiling issues with prolonged lugging of the motor and fuel mileage issues if kept above 2k. This whole issue is fueling my debate between sticking with the 3:55's or stepping up to the 4:10's. Let me know what you guys think. Thanks!

MIke

 

Your truck and tranny would be happier at 2000 rpm than lugging at less than 1500 rpm!!

 

My truck gets great milage running at 2000 RPM constant. I drive at this RPM everyday in 4th gear because I am a few miles an hour below being able to hit 5th gear due to the 5th gear nut issue at speeds below 1600 RPM. Rev it and dont worry about it. MPG issues come more from aerodynamics/speed than RPM.

 

i run my truck at 2800 2900rpm all day... no worries

Justin

 

Lugging it is one of the worst things you can do to any engine....

 

MDM;
The engine doesn't suffer as much as the drivetrain.
Your auto OD unit is taking a big beating at those rpms.

Use the power range a #10 plate and GSK offers.

 

It is the lugging also that loosens most parts, because you are trying to work the engine in its not so optimum RPM range.. The vibration is greater and it loosens stuff..

Tx

 

Interesting responses. The best way to determine where to run your engine is through the use of your pyrometer. Keep the EGT between 550 and 800 for normal unloaded driving, and between 800 and 1250 for situations where you are loading the engine.

This particular version of the B series engine is designed to run best when between 1,500 and 2,500 rpm, and as long as you keep your EGT's in an efficient range you are not harming the engine. Just do not let it rattle from lugging at low rpms, and it is simply pointless to rev it beyond an efficient load range, and it will crank well over 3,000 if you have tweaked the governor a click or two.

Listen to the engine as it works, and you will develop an ear for when it is working at its best efficiency based on the load, rpm, and EGT. It develops a tone to the exhaust when it is running efficiently and that is what you will listen for.

 

I know this tone very well (5" stacks, missing muffler ) I like running the truck at the higher rpm vs the lower rpm, but I thought fuel consumption would be more of an issue than it apparently is. The point "robert chilton" made about aerodynamics is a very valid one that I didn't think about. According to some of the gear calculators I've used, 4:10's would put me nearly back to stock rpm's at cruising speed. I know I've been beating the 3:55 vs. 4:10 debate to death , I should just do it and be happy!! Thanks for the words of wisdom guys!

MIke