The new Cummins V6 and V8 engines

The new Cummins diesel engines have been in development for over 9 years now. Cummins partnered with the Department of Energy to meet EPA Tier II and CARB LEV II emissions standards. The engines are designed for vehicles that have a gross vehicle weight of 8500 pounds or less. That means that the Dodge Heavy Duty trucks will likely not see these engines (although I predict that the 2500 will be offered with the V8 as a base engine).

These new engines are a V6 and a V8. The V6 is 4.2L (256ci) and the V8 is a 5.6L (342ci) engine. Both use a 90 degree design with an iron block and aluminum heads. These engines are state of the art with a new EGR (Exhaus Gas Recirculation), a turbo, SOHC (singe overhead camshaft), piezo injectors and a particulate filter. They weight in at 663 pounds and 788 pounds for the V6 and V8 respectively, both weigh significantly less than their big brother, the 6.7L inline 6 that is in a wide variety of vehicles including the Dodge 3/4 ton, 1 ton, and Chassis cab Rams.

Even though they are smaller, Power isnt a problem for these engines. The 4.2L V6 produces 270 hp and 420 lb-ft of torque. The 5.6L V8 has 325 hp and 500 lb-ft of torque. These numbers are accurate for now, but these engines are a couple years from market. Diesels are notorious for being easy to add power with just a change to the PCM so expect them to change a bit to meet what the market is putting out at the time.

Acceleration with one of these under the hood is surprisingly fast. Diesels typically are slower because they have low horsepower and a crap ton of torque. The low horsepower is made up for with a turbo fitted to the engine from the factory to boost acceleration. The caveat with a turbo is that it needs time to spool up before it can start adding extra power to the engine. This extra power kicks in a second or two after the throttle is stomped to the floor. Cummins has relieved this problem with a new variable geometry turbo. The turbo increases the spooling at low rpm (sitting idle at a stop light) so that the "turbo lag" is reduced. The result is these diesel engines have a lot more pep off the line that diesels in the past.

Even more impressive than the acceleration is the emissions control in the new Cummins engines. 2007 federal guidelines that allow for no more than 0.07 grams of nitrogen oxides per mile and 0.01 gram/mile of particulate matter (soot). To conform with these regulations the engines use a catalytic converter, particle trap, and EGR system.

The EGR system has pipes that cool and redirect some of the exhaust back to the engine intake. These gases are used to cool the combustion that goes on inside the engine. The gasses that cant be used to cool combustion are instead redirected to the turbo pathway.

Cummins located the catalytic converter near the engine so that the engine will warm up to optimal operating temperature faster. This location also makes the entire configuration smaller than most diesel exhaust systems allowing this to be more easily mated to smaller SUVs and pickups. The Diesel Particulate Filter (DPF) is a honeycomb 4 way catalyst that processes the exhaust soot until it meets EPA standards. There are sensors placed around the DPF that measure air flow and can adjust the exhaust temperature to burn off of any blockages that occur. This part of the system is sophisticated and costly, so durability is a concern. It has been tested to work for 150,000 miles and still operate efficiently.

The fuel economy of these new engines is probably their biggest advantage over a similarly sized gasser. These engines running on Ultra Low Sulfur Diesel produce great power and give excellent mileage. For comparison the Durango fitted with the currently available 4.7L gas engine has a combined city/highway mileage of 15.3, the 4.2L V6 was tested in the Durango achieved 22.1 in city/highway driving. Highway alone was 25 mpg,an overall 44% improvement in mileage. The 5.6L diesel was put against the 5.7L Hemi engine in the Dodge Ram 1500. In a test of city/highway driving the Hemi is rated at 14.6 mpg while the 5.6L Cummins made 21.7. In a test of highway mileage the 5.6L diesel engine made 24.6 mpg, a 49% improvement.