In the Dodge application, the rpm of the advertised or maximum rated power of the engine is 2500 rpm (prior to 1996 models), 2600 for 1996 and newer models with 12-valve manual transmission and 2700 rpm for 24-valve. Peak torque is reached at 1600 rpm on all models. The Maximum Full-Load Governed Speed is 2800 rpm for 12 valve and 3200 for the 24-valve. The Maximum No-Load Governed Speed is 2950-to-3300 rpm (3500 for 24-valve).

Therefore, your normal operating range for the engine is between 1600 (peak torque) and rated rpm (2500-to-2700, depending on your model). These engines should not exceed 2800 or 3200 rpm downhill (depending on model year), under load, since that is the governed speed of the engine. At no load (i.e., if you were to push the accelerator to the floor and hold it, sitting still in neutral), the no-load governed rpm is about 10 percent over the full-load governed rpm.

The engine is designed for maximum torque or twisting power at lower RPM (1600 rpm), for hard pulls on long grades. The torque curve of the engine is nearly flat from peak torque (1600 rpm) to rated power (2500-to-2700 rpm), however, torque does drop off slightly near the rated power rpm. Typically, the 'sweet spot' rpm for cruising would be about midway between peak torque and rated engine rpm, however, any rpm between peak torque (1600 rpm) and rated speed is fine and will not harm the engine. Overspeeding above rated speed and lugging the engine under load below peak torque is not recommended.

Also we mention that on downhill operation, the weight of the truck and any load you have on it, or towing, will cause the rpm to exceed governed rpm. Even though the engine is governed while under power, the load can push the engine beyond its rated speed. We would not recommend going too much over the no-load governed rpm or you could cause valve/piston contact, which can cause major engine damage.

Any rpm between peak torque (1600) and full-load governed rpm is acceptable and will not harm the engine. However, if you are concerned about fuel mileage and long engine life, then the lower rpm is recommended. At higher rpm's, the engine uses more fuel and all internal components turn faster and wear out quicker, which will shorten the life of your engine. There is less horsepower and torque at maximum rpm and the only reason to run the engine at maximum rpm would be for higher road speeds.

For the best fuel mileage, Cummins engines should be operated between peak torque and rated speed. Do not lug the engine when running in this RPM range. What is "lugging"? Lugging the engine is when, at cruising speed, the engine is accelerated and it will not increase the vehicle speed. Also, lugging is operating the engine, under full load, below peak torque rpm.

We do not have information about shifting into or out of overdrive in the Dodge application, since Dodge designs and supplies the transmissions for their products.

If your engine is still within the Dodge warranty period or you need information about the Dodge Ram truck, please feel free to use the Dodge dealer locator or contact Dodge: (http://www.4adodge.com/frameset_main.html?dealers/index) on the Dodge website (http://www.4adodge.com/).

We thank you for your interest in Cummins products. Please let us know if you need assistance in locating the nearest Cummins-authorized Dealer or Distributor Service Provider. For assistance in locating a Service Provider, feel free to use Cummins North America Dealer Locator, which can be found on Cummins website:
http://www.cummins.com/service_locator/index.cfm

Please let us know if you have other questions and if away from your computer or have a time-critical request that needs more urgent attention, feel free to call us toll-free (from North America) at 1-800-DIESELS (343-7357). Customers may also call Cummins switchboard 1-812-377-5000 (worldwide toll call) and ask for the "800-DIESELS Call Center" for assistance.

Email direct: powermaster@cummins.com