The second in what will become a four-displacement family of the Heavy Duty Engine Platform (HDEP) from truck maker Daimler has been unveiled as the DD13 from Detroit Diesel. At 12.8 liters, this complement to the DD15 launched last fall is shorter and lighter, with power ratings from 350 to 450 horsepower and torque from 1,350 to 1,650 pounds-feet.

A new block, head rods and rotating parts mean an engine that is 400 pounds lighter than the DD15 (which is itself around 20 pounds heavier than the Series 60 installed in the chassis.) With significant weight savings and good horsepower and torque, the 13-liter is targeted at the vocational and bulk operator. It gains some weight savings from its single stage asymmetric turbocharging: at the engine's production launch in January 2009, it will have no turbo compounding like its bigger counterpart. Instead, the area around the rear-mounted accessory drive is kept clear for a rear mounted power take off which is often required in vocational applications. A front PTO is also offered.

Later, a turbo-compound version will be offered, which is likely to go as high as 500 horsepower for on-highway applications.

Like the DD15, the DD13's main components are made in different locations around the globe, with connecting rods from DDC's plant in Redford, Mich., heads from the Mercedes-Benz foundry in Mannheim, Germany, and block castings from the foundry in South Africa. Machining of the heads and blocks as well as engine dress will be in Redford for the DD13 on the same assembly line as the DD15.

The 12.8-liter version of the HDEP will be launched - like the bigger 14.8-liter DD15 - first for NAFTA. It will be installed in Sterling first, then Freightliner and finally Western Star, all before 2010. It will replace the MBE4000, which goes away for the next emissions step in January 2010. Ultimately, the worldwide family of HDEP engines will encompass 10.6-, 12.8-, 14.8- and 15.6-liter displacements. Initial plans called for the top three to be available in NAFTA countries, with the smallest for Europe and Japan. However, there is now discussion about bringing in all four for North America.

The 12.8-liter DD13 has a smaller overall size than its bigger counterpart, accounting for the lighter weight. While looking very similar - around 65 percent of the parts are common - the engine not only has a smaller displacement, but bore centers are also closer to make it a shorter engine overall. Like the DD15, camshafts are built-up hollow shafts with a rear-mounted camshaft and accessory drive. Blocks are gray cast iron and heads are CGI. The engine is robust - accounting for some of its 2,200-pound weight - and has a B50 life of 1 million miles.

Using the same Amplified Common Rail Fuel System (ACRS) as the bigger engine, the DD13 is claimed to offer exceptional fuel economy. The fuel system has a two-stage pump to lift fuel pressure to the rail that is then amplified to as much as 32,000 psi in the injectors. This, says DDC, means less chance of fuel leakage from the ACRS unit.

The engine is designed for long service with 50,000-mile oil and filter changes. Because of its close similarities to the DD15, most service parts are already at the dealers, and the technician training requires only an Internet based update in addition to the five-day course for the DD15.

ON THE ROAD

A brief - surprise - opportunity to drive the new engine was afforded at the Sterling show-and-tell in California's wine country of the Napa Valley. A 20-mile circuit with only a few short hills but many tight turns and stop-and-go traffic lights showed the DD13 pulls down well. It doesn't have quite the grunt of its turbo-compound counterpart, but it will lug down to 1,000 rpm - or lower - and pull away without complaint. Peak torque is between 1,100 and 1,500 rpm, so for all practical purposes the engine operates just about all the time on peak torque.

I drove it using for the most part only around 1,200 rpm, where it pulled strongly and quietly in a Sterling demo truck. It was coupled with a 10-speed Eaton Fuller transmission, which it will likely see in many applications, and it was a good match, rolling off 200 to 400 rpm between shifts according to road speed. With a nice automated transmission, this 13-liter would be an absolute delight for any driver, but even with the manual, the engine's fast roll-off makes upshifting easy and the prompt throttle response makes finding a lower gear easy as well. All in all, it's an engine that is easy to get to grips with, even at first meeting.

The DD13 will go into production in early 2009. It is predicted to offer improved fuel consumption of around 5 percent over the MBE4000, and with its 350 to 450 horsepower spread and relatively light weight, it should be extremely popular in Sterling and Freightliner chassis.