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Test Drive
DDEC VI: Rarin’ to go

By Paul Abelson
senior technical editor

In the 15 years since I earned my CDL, most of the test drives I’ve taken have been to evaluate new trucks. Rarely do engine makers bring out new engines to be test driven.

Most trucks use highly evolved versions of well-established engines. The only instances I can remember when the motor, not the truck, took center stage were when Caterpillar introduced the 3406E, their first electronically managed engine, and when Cummins came out with the ISX, the engine designed to take them through 21st century emissions regulations.

It was those regulations, specifically those in effect for 2007, that led me to request a test of the latest Detroit Diesel Series 60. It powers Freightliner, Sterling and Western Star, and is quite popular among owner-operators. It has a reputation for fuel efficiency and durability. Quite a few owners have more than a million miles on them.

To discuss how the truck and 2007-compliant engine were designed to work together, Detroit Diesel Staff Application Engineer Chuck Blake, a Technology & Maintenance Council veteran and Silver Spark Plug recipient, came along on the test drive.

Chuck explained how Detroit Diesel integrated the engine to make it function in the truck. He brought another engineer, Karthik Natarajan, to demonstrate some of the electronic wizardry that makes it all work.

During the pre-trip, Chuck pointed out changes made to the new Freightliner Century Class to accommodate the new emission control components. Most obvious was the one-third larger radiator, mounted directly to the engine.

This cuts way down on movement and allowed a much tighter fit between the fan shroud and the fan blades. That results in better air flow and cooling as well as improved fuel efficiency. With less relative motion, hoses and hose clamps should last longer for reduced maintenance.

The engine gas recirculation valve was moved to the cool side of the engine. Chuck noted improvements to the EGR cooler, and other steps that have been taken to improve component life and reduce maintenance costs.

The diesel particulate filter, or DPF, is part of the after-treatment system, which is tucked under the sleeper, inside the frame rail. It’s positioned safely away so no one can accidentally touch the unit, especially when it reaches 1,100 degrees during regeneration or cleaning.

The Freightliner sat on a 228-inch wheelbase. With its 70-inch raised-roof sleeper, my test truck weighed in at 18,140 pounds with full fuel tanks. The 48-foot trailer was loaded with concrete ballast and grossed out at 74,140 pounds.

Before we set out from Detroit Diesel headquarters, Karthik wired his laptop computer to the DDEC VI – the engine’s electronic control unit. He put it on the dashboard so we could see the various performance readouts. He explained what the computer was sensing, and what it was telling the engine to do.

Our route was selected to provide a variety of driving situations, from tight corners on city streets in Detroit to long, relatively steep – 3 percent plus – grades on Michigan Highway 14 east of Ann Arbor.

The typical fleet-spec engine had 455 horsepower Detroit with 1,550 lbs.-ft. of torque. It was coupled to a 10-speed Eaton Fuller overdrive transmission with a 17.1 to 1 overall ratio. With the 3.58 to 1 Alliance drive axle and 11R22.5 lug pattern traction tires, performance was certainly adequate.

Our turnaround point was at a truck stop in Ann Arbor. Before we got there, Karthik started regeneration in the after-treatment system. Inside, the system heats to about 1,100 degrees, so you don’t want to regenerate while standing still. The truck must be going at least 5 mph, because airflow helps cool the after-treatment system. The computer automatically shut the process down when I slowed on the exit ramp. By the time I was parked, the system had cooled considerably, enough to leave it safely.

There is also an override to prevent regeneration if you are in a hazardous area, such as driving around a refinery or chemical plant, where the after-treatment system could ignite fumes.

After coffee, Karthik played with the computer and gave me Detroit Diesel’s most powerful owner-operator rating, 515 hp and 1,650 lbs.-ft. of torque. The torque was rated at 1,100 rpm, and stayed level to 1,500 before falling off.

At 800 rpm start up, the engine has 940 lbs.-ft. of torque. It pulled smoothly below 1,000 rpm in low range in any gear. The high torque multiplication through the gears and low speed torque make the Detroit easy to drive and very forgiving of missed shifts.

Climbing the grade on Highway 14, I was able to stay in ninth gear, running between 55 and 60 mph, not blocking any other trucks and even passing a few.

I checked the ProDriver, the driver message center, to see what fuel economy I was getting. My target was 7.0 mpg.

The ProDriver display has a bar showing to the left of center if you’re running under the target and to the right if you’re beating it. The length of the bar shows how much better or worse. I did a tiny fraction under 6.5 mpg, but I wasn’t driving for maximum fuel economy. With limited time for the test drive, engine performance was my primary objective.

Back at headquarters, Chuck downloaded the trip data from the DDEC VI controller. It confirmed my fuel mileage, showed that I spent about 10 percent of my time loading the engine to 90 percent or more – no wonder I didn’t reach 7 mpg. But, I did cruise 60.9 percent of the time between 1,200 and 1,500 rpm.

There’s a great deal of information in the engine computer. Even with older generation ECMs, your dealer can print out your data for a specific trip or overall performance. Then you can do your own analysis to see where your driving can improve.

I’ll admit that less than a day isn’t nearly enough time to evaluate an engine, but first impressions are that:

  • Early 10/02-engine reliability issues have all been addressed;
  • After-treatment systems will not affect performance; and
  • The improved variable geometry turbocharger and computer-controlled fuel system together improve response to driver input.

Paul Abelson may be reached at