What you said was dead on, for a 1st gen Cummins. Not so for a CR engine.

On a stock 600 series engine peak TQ is 2400-2500 rpm's. At 1600 it is defueling so hard it is in lug mode all the time unless the fueling curve gets midified by a programmer. Minimum BSFC is right at 1900 rpm's on a CR engine, published Cummins specs. Trying to do anything other than just roll and empty truck under 1800 rpm's will gain nothing and quite likely lower the expected life.

The 6 speed trucks do suffer from excessive rpm's due to the .79 OD on them. A gear vendors on a 2x4 with stock or smaller tires is a good combo unless you are towing heavy.

With out breaking the bank, a programmer that will change the timing, a good air system, a free flowing exhaust is about the best you can do without major mechanical changes. 70 mph is about the break point when overcoming the aerodynamic equation starts defeating the efficiency. Not much you can do about that but drive slower and enjoy the scenery.

 

No Schizenburgh! I frieken KNEW IT. Blessed Torque Management.

With that said, could my mileage be in the toilet because I'm shifting under 1600 rpm?

Ryan

 

Our compression ignition engines will achieve their best fuel mileage at approx. 1800 RPM...

Peak torque happens between 2600-2800 RPM...

Programmers can change those numbers...

That's when you need to replace all the factory turbo's, fuel systems, etc., to keep up with all the parameter's that agressive programmers can change...

The inline six design of the Cummins is more efficient at lower RPM's than say a Duramax with it's V8...

But those D-Max's in turn can spin a lot more turns without blowing stuff up like we do...