Trio of Ts: Show Basic Strengths

By Tom Berg, Truck Editor | September 28, 2010


A setback steer axle identifies a T series truck, like this T800 dumper. It's got a Cummins ISM with an Allison automatic.

This mixer has a forward-set steer axle, so it's not a T800 (in spite of its sloping hood) but a W900S. It's got a lightweight Caterpillar C9 and an Eaton 8LL manual.

The T800H heavy haul tractor looks impressive just sitting there, even without a loaded trailer. Its wide hood houses a big, high-capacity radiator and (inset) 600-hp Cummins ISX.

Third T model in our trio is this T660 Extended Day Cab tractor, which would give cargo onthe flatbed trailer, not to mention its driver, a smooth ride. It's got a Cat C13 with an Eaton UltraShift.
 

Stack on the Cat-powered W900S includes the big diesel particulate filter, which looks like and doubles as a muffler, with a Clean Air Induction pipe that leads from the DPF back to the engine.
 

T800H's driver can check the temperature or pressure of almost any moving thing on the truck. Want more gauges? Go fly a Boeing 747F.

How good is your knowledge of trucks? If you run Kenworths, you might already have noted that one of the three supposed T800s pictured here is not a T model, but a W. The hoods look the same, so what's the difference? Placement of the steer axle. KW's T800, and all T models, have a set-back steer axle while the W900's is forward-set.

Many "W9" trucks built for vocational use have an S suffix, as does the mixer chassis shown here. Highway models (usually they're long-haul tractors) are suffixed with a B (signifying the second major redesign of the series) or L (meaning long, for its extra-length hood). So no matter what the hood looks like, it's the position of the steer axle that identifies the basic model, and it's a detail that's peculiar to Kenworth.

So why the "trio" in the headline? Because for this article I drove not only a pair of construction-type T800s, but also a T660, specifically a Day Cab version of KW's popular highway tractor, which began life as the aerodynamic T600 "anteater" of 26 years ago. Its latest iteration includes smoother aero lines and interior upgrades, which merits the model 660 moniker. The new Day Cab is something that can ably pull flatbed trailers laden with building materials or bottom dumps with sand or aggregate for a concrete batch plant, and its setback axle allows a tight wheel cut that makes for good maneuverability.

Install a higher-capacity axle and big "duplex" tires, as was done with the "T8" trucks, and turning ability is not as good. But, of course, more weight can be carried up front, which is another advantage of the setback placement that's usable in "axle-weight" states. In "bridge-formula" states, which encourage spreading out the load over longer distances, the set-forward steer axle stretches a wheelbase and allows heavier payloads. That's one reason why KW makes the W series, and the mixer also has the heavy front-end parts.

However, the point of this driving exercise in late February was not the T versus W distinction, but the workability of the EPA '07-spec diesels that powered the trucks. All had Caterpillar or Cummins engines with advanced electronics and combustion designs, and exhaust aftertreatment that you've heard so much about. KW titles trucks with these engines as 2008 models. Builders want customers to know that the diesels have been extensively tested and run well, and figure we press guys can help get out the word.

KW's public relations manager, Jeff Parietti, staged a multi-truck event out of the tech center run by Paccar, parent to KW and Peterbilt, near Mount Vernon, Wash., north of Seattle. He and his colleagues gathered 16 trucks and tractors and about a dozen reporters, then girded their nerves as those of us with commercial driver's licenses went off on short trips through the area. In spite of chilly and threatening weather (it rained intermittently and snowed heavily that night), we all enjoyed the jaunts, as much for the scenery (the rolling terrain is punctuated with rivers, estuaries and bays) as for the driving experiences.

Gutsy new engines

I can't say how long these complex new engines will run without trouble, but they certainly run well when relatively fresh from the factory. Previous drives with a variety of '07-spec diesel makes and models show that they are gutsy and burn cleanly, to the point where you cannot see any exhaust smoke or smell any odor. The diesel particulate filters that most diesels are now getting include ceramic honeycombs that cause back pressure, but that's taken into account in their tuning and the new engines feel just as powerful as before.

Caterpillar diesels include Clean Air Induction, which is Cat's version of exhaust-gas recirculation (EGR) that Cummins and others have used since October '02 to lower combustion temperatures and reduce formation of oxides of nitrogen. People at some truck manufacturers have complained about installing the CGI's return pipe, that takes filtered exhaust gas from the rear of the particulate filter to the engine. But Kenworth engineers didn't find this too difficult, according to Ben Vander Griend, an assistant chief engineer in charge of powertrain and chassis development.

The T660 Day Cab had a 470-hp 13-liter Cat C13 mated to an Eaton 13-speed UltraShift, and they worked very well, though the engine tended to rev higher in each gear than necessary. Vander Griend, who rode with me in this tractor, pointed out that the automated tranny's electronic controls can be programmed to shift sooner, which many owners would do to get better economy. The W900S mixer truck had a lightweight 9-liter C9-350 with an 11-speed Eaton 8LL, which like most manuals that KW expertly installs, was easy to shift and a joy to operate.

The two T800s had Cummins power. The dumper had an 11-liter ISM-425 and a six-speed Allison 4500RDS automatic, which your grade-school principal could drive with only a little coaching. This one was lively right off the line and throughout the rev range, without the lower-rpm dogginess that I've experienced with other engines saddled to heavy-duty Allisons. Are the new diesels better tuned for automatics? I don't know, but this ISM seemed so.

The stout-looking tractor was a T800H, built for heavy hauling. It had an extra-wide hood to house an extra-large radiator (1,780 square inches) needed to cool high-horsepower engines at low road speeds. This engine was a 600-hp ISX, which Cummins has reintroduced after withdrawing the much-advertised Signature 600 in October '02. Engineers weren't sure it would live with the then-new EGR, which causes the engine to run even hotter, but now they are. It was hard to judge its power on this day because I drove the tractor without a trailer.

It had been hitched to a heavily ballasted tri-axle dropdeck semi, but another writer (who shall remain unnamed, but it wasn't me!) dragged some of its wheels over an obstacle, blowing a tire and bending a rim. Technicians detached the trailer, but the tractor looked so impressive that I drove it anyway. Even bobtail the hulking T8 was satisfying to operate, with that big hood out front, dual stacks out back, and all those big-tired axles following along. And it had more gauges and switches in its dash than any other truck I can remember.

On the road again

The tranny was an Eaton 18-speed, and with 600 horses, 2,050 pounds-feet of torque, and no load except the tractor's own mass, it could be shifted like a six-speed. That's what I did (4th and 5th in Low range and 6th through 9th in High), but I did split some of the gears as I rolled up and down hills and followed speeding and slowing traffic. The CumminsIntebrake was strong enough to stop the tractor on its own except as I drew to a stop, and the engine throbbed as it pulled down road speed.

The cabs on the T800 and W900 series are KW's stout aluminum design, and are so air-tight that I had to crack open a window when I wanted to close a door. This got a little annoying, but it does imply durability and longevity. Meanwhile, drivers enjoy soothing quietness and a reassuring feeling of quality. Interior trim packages provide comfortable surroundings, even in base levels, along with professional-looking instrument and control panels. Big windows that are close to a driver's eyes due to the cabs' narrowness provide a fine view of the outside world. The T800 dumper and the T660 tractor had the Extended Day Cab option, with an extra 5 inches of length and more belly and leg room. So a T- and W-type cab can be quite roomy, even if it is a little narrow compared to some others, including that on KW's own T2000 highway tractor.

If you run Kenworths you probably know all this. Eventually you'll be buying some with the new diesels, and aside from coughing up an extra $6,000 to $10,000 or so per truck, you'll have to get accustomed to the engines' extra complexity and the added maintenance they will require. The engine makers say it won't be much, but users report that EGR valves and turbochargers on some '02/'04 diesels have proven troublesome, and we can only hope that the '07s are better. In the meantime, your drivers will truly enjoy themselves if they're in KWs like these.

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