Detroit on Dirt!

I've been lucky in my time behind the wheel, having had a crack at a wide variety of different jobs that all come under the "truck driver" banner. One of the things I haven't done is truck and dog work, so when invited to drive a Western Star truck and dog " fitted with the new Detroit Diesel DD15 engine " I jumped at the opportunity. Having been impressed by the updated DD13, I was looking forward to seeing what the larger 15-litre power plant had to offer, while at the same time experiencing a different combination to those I had driven before. Never a dull day in this job!

The DD15 is the latest, and largest, offering from Detroit Diesel for the heavy truck market here in Australia. (The 16-litre DD16 hasn't been officially released yet, though there was one fitted in a Western Star on display at the Brisbane truck show). Available in power ratings from 475 hp/1,650 lb.ft to 560 hp/1,850 lb.ft, this engine uses a combination of very high fuel injection pressure, exhaust gas recirculation (EGR), and a particulate filter to keep emissions within Euro 5 specifications.

The use of a non-variable, wastegated turbocharger harks back to days gone by, but combined with the benefits of turbo compounding, delivers good response to pedal input with virtually no turbo lag. Detroit Diesel is also spruiking the fuel economy benefits of this setup, though our drive was anything but a fuel economy run.

The truck we drove was fitted with the 500 hp (368 kW) version, which puts out 1850 lb.ft (2,508 Nm) of torque. A look at the spec sheet shows that the maximum horsepower comes high in the rev range, at 1,800 rpm, while the torque peaks at around 1100 rpm, promising very strong low-down pulling power. Slotted in behind the Detroit was an Eaton 18-speed manual gearbox, these transmissions still being a popular choice among tipper operators.

Now, as I've said, I'm a newcomer to this area, but I still don't understand the preference for manual gearboxes. The benefits of AMT gearboxes are becoming clearer every day, with reductions in tyre wear, fuel consumption and damage to components such as clutches and differentials. The option of selecting and staying in a certain gear is available on every AMT I have driven, and given the amount of time these trucks spend on the road, versus off the road, surely the benefits of an AMT would be obvious in this field as well. I am open to discussion on this"

In the interests of good reporting, we like to put our test trucks to work in the job for which they were designed. For example, for our highway prime mover tests, we do a run (generally Melbourne-Sydney), fully loaded and within realistic trip times. For the lighter rigids, we put them to work around town for a day or two, in their intended environment. This allows us to get past the new truck smell and big chrome pipes, and tell you what really matters " how it performs in the real world.

To do this, we occasionally enlist the help of operators who have the right kind of loading for the vehicle in question, and for our tip truck and dog test we were kindly accommodated by the team at Bakers Landscape Supplies, from Cranebrook, just west of Sydney. Bakers runs a mixed fleet, including Western Stars, Macks, Sterlings and a Kenworth, carting sand, rock and garden supplies throughout New South Wales.

Our run took us west from Penrith, over the Blue Mountains to pick up a load of crushed rock, before returning to Cranebrook via the Bells Line of Road. As you would expect, the empty run up the mountains was uneventful, with the truck and dog unit weighing in at just under 17 tonnes and 500 hp on tap from the DD15. Surprisingly, the ride was very good while running empty, with the only drama encountered being a little wheel slip when moving off at the lights due to the wet conditions.

After loading at the quarry, and now grossing just under 47 tonnes, the true test of the DD15 really began. The route along Bells Line of Road was deliberately chosen as a test of pulling power, but also to test the engine braking and handling at the same time.

Thinking back on days gone by, the one word you would not associate with a Detroit engine is "quiet". This engine turns that on its head. From idle right through to maximum working load, this engine produces very little noise. Also noticeable is the lack of vibration, with the DD15 running very smoothly until the revs drop to around 1,000 rpm under load. Even at 1,100 rpm, though, the engine is smooth, while still producing maximum torque. Inside the cab, noise levels were very low, making conversation easy, even with a window open.

Inevitably, the conversation turned to a comparison between this truck and those in the Bakers' permanent fleet. Our guide for the day usually operates another brand of truck, with a smaller capacity engine rated at the same horsepower. The difference in torque output between the two was obvious with the DD15 cresting the hills one and a half gears higher than the smaller powerplant (which would also be well run in, as opposed to the new Detroit in our test truck).

The pulling power of the DD15 really shone through at one particular point, where a very tight left-hand corner becomes a very steep, low speed uphill drag. Just when the engine sounded like it was about to give up, the torque kicked in to maintain the gear and eventually accelerate up the hill. No mean feat at a weight of 47 tonnes.

The downhill stretches showed the strength in the upgraded Jacobs engine brake. What was surprising here was that the engine still maintained its low noise level, even under full engine braking. This is partly due to the diesel particulate filter mounted in place of the vertical muffler, which, along with the use of amplified common-rail fuel injection and EGR, helps this engine meet Euro 5 emissions standards. It will be interesting to see how the DD15 is accepted among those who like a bit of noise from the exhaust, and how long it is before they find a way to get it.

While this was not a test for fuel economy, it did demonstrate some other aspects of this engine. This engine is the absolute opposite to the Detroit Diesel engines of the 70s and 80s. Gone is the need to wring its neck to get any power, gone is the screaming noise that could be heard from miles away, and gone is the plume of black smoke that filled the air whenever the accelerator was pushed floorward. While those who designed this engine will tell you it is Detroit Diesel through and through, the evidence would suggest otherwise. Here is a quiet, clean engine with plenty of low-end torque and excellent driveability.