@Dept:
KW's T660
Chassis and cooling enhancements that accommodate ‘07 engines bring big benefits to the new aero.
Steve Sturgess
Executive Editor
It was a year ago that Kenworth unveiled the T660 at the Mid-America Trucking Show to admiring crowds. The stylish replacement for the venerable T600 – it celebrated its 21st birthday last year – is engineered for the 2007 engines and will carry the additional sticker price that comes with this new technology.
But in introducing a new model, Kenworth is adding content to the T660. So essentially, what you get is more truck for your buck.
You also get a lot more style. There's the new hood, of course. A new hood would have been required in any case to accommodate the '07 cooling package and, most likely, the physical size of the new Caterpillar C15, one of a number of Cat and Cummins engines available.
But the styling of the hood is a major advance over the earlier T600: a larger, sparklier grille opening with a well-rounded crown and additional cooling openings in the new, two-piece bumper. Sleek, high-output headlamp modules are complemented by driving lamps in the bumper cutouts, and there's a common flow to the sculpting of the headlamp, the step and the side skirts. Even the repeater lamps in the trailing side of the fenders share the same cues.
The surprising thing is how well the new styling works with the essentially carryover cab. There are the DayLite doors and the one-piece windshield to lighten the cab surfaces, and the air inlets high on the hood carry the same styling theme up toward the cowl-mounted mirrors with their simple but effective aero brackets.
Under the hood, the T660 has only 2007 engines from Caterpillar and Cummins. Both are fully engineered and both makes are available immediately. Because there were a number of trucks built in '07 with '06 engines from inventory, all Kenworth trucks with the latest technology engines are sold as '08 model year trucks.
For this abbreviated test, we ran a few miles during the free-for-all driving day, then took the truck for a more exclusive run, covering in total more than 200 miles. Day 2 saw myself and Jim Park from HighwayStar – our sister Canadian publication – on one of the most scenic drives you can imagine.
Our route headed west from the Paccar test center near Mt. Vernon north of Seattle towards Anacosta, then cutting southwest to cross over the high, narrow bridges of Deception Pass to Whidby Island. From there we followed Route 20 as far down the narrow island as we could, to the ferry terminal in Clinton. There we retraced our steps and, somewhat grudgingly, handed over the keys to the truck back at the test center.
The Truck
This was a nicely outfitted T660 with a 72-inch sleeper. We were given this unit as one that is more appropriate to the HDT audience than the big 86-inch Studio Sleeper that is also available on the T660. But the fact that it also featured Kenworth's anti-idling Clean Power technology made this T660 particularly interesting in light of our special fuel issue this month (see story on page 108). Clean Power is a Kenworth exclusive and addresses anti-idling without resorting to an onboard auxiliary power unit, a move that could set Kenworth ahead of the game given upcoming restrictions on the use of APUs, especially in California in 2008.
Clean Power allows for shutting off the big diesel under that nicely sculpted hood – in this case a 15-liter Cummins ISX500.
The 500 is available with 1,650 pounds-feet at 1,200 rpm, as here, or with 1,850 at the same engine speed – or with both in the SmartTorque rating. But this 1,650 was perfectly adequate and allowed matching to the 13-speed Eaton Fuller UltraShift LEP transmission, which is rated for this torque.
The engine, of course, featured Cummins 2007 components, which include exhaust gas recirculation as with the '02 engines, but now with the EGR valve relocated to the cool side of the engine. A few minor changes to the block improve coolant flow, and the Holset variable geometry turbo now has electronic controls. This change now gives closed-loop control to the VGT, allowing more precise air management and even better throttle response – a big plus that came with the adoption of the VGT back in 2002.
The cooling package is sized up again for the higher rates of EGR flow, and there's a fan ring mounted to the engine to minimize fan tip clearance – though we did note there was a good <+>3/<->4- inch clearance.
At the other end of the engine, there was plenty of clearance all around for getting in and working. The ISX is a clean engine without much external pipework, and it looks tidy even with its EGR stuff.
The big red engine is otherwise largely unchanged for '07, except that a diesel particulate filter is part of the engine package. On the Kenworth, this mounts to the frame beside, and parallel to, the driveshaft with a single stack exiting to the rear of the sleeper. We noted the diffuser at the top of this stack. No explanation was offered except it draws in air to cool the exhaust, most likely during an active regeneration event. It also hides the tip of the exhaust, which we have noted can turn blue with exhaust heat. Uncannily, the inside of the turned stack tip was bright and shiny, as all 2007 stacks will be throughout their lives.
The drive axles were Dana DSP40, with 3.55 ratios. There are no special gearing requirements for the Cummins '07 engines, and these ratios give a good top-gear performance with 60 mph at 1,300 rpm with the 75R22.5-inch Bridgestone rubber. A single, automated split down brings rpm up to 1,500 or a whole gear to 1,800 for the jump-up grades on our test route.
Suspension is relatively new under the Eaton E-1202i front axle, still featuring the long springs that gave the T6 such a good ride. They're designed to react to the strong braking torque available with the Bendix air disc brakes spec'ed for the front of this T660. Regular S-Cam Bendix drums were on the rear wheel positions. And catching my attention, the rear suspension was the Kenworth AG380. This is the funky-looking air suspension with the curving spring lower arm location first used by Peterbilt. It looks a little odd, but it is very light and I have found it to be a truly excellent-riding suspension.
Steering was by TRW TAS-65 and tires were Bridgestone R287 up front and M720FE on the drives.
The Cab
As I popped open the driver's door, two things struck me immediately. The first was the way lamps in the door and over the step have been positioned to throw light down for a safe climb up at night. The other was the way the step treads have been integrated into the design of the fairing. However, I didn't see how these fairings come off. The fuel tanks behind the side skirts have their filler necks located at the back end, keeping diesel fuel away from the step area.
Up in the Kenworth seats, Jim Park and I both appreciated the gorgeous new dash. It's not new on the T660, having been introduced a year ago, but that doesn't stop it from being an excellent combination of form and function. I have a slight quibble with the location of the driver display panel where it can be obscured by the steering wheel rim, but the arrangement of the instruments is pleasing to the eye, and the grouping of the switches is a treat for the fingers. The steering wheel has spokes that sweep down to minimize obscuring the instruments, and while this T660 didn't have them, there are optional switches that mount in the spokes.
There is a multifunction turn-signal stalk that needs a little familiarity to get to all the functions, such as the windshield wash, but it is soon learned. Less well placed is the ignition switch, down where you sweep your right knee past when climbing out. One of us bent the key during our time with the truck. (Kenworth is not alone in positioning the key down here. I broke off a Volvo key in the ignition in exactly the same way last year.)
The vision forward is good, with the slope of the hood allowing sight to the ground only 20 feet out. In rain and snow, which we experienced up in Washington, the visibility is enhanced by the "clap-hands" overlapping windshield wipers that clear a wide sweep of the glass. To the sides, the DayLite doors give close-in sight to the ground on both sides of the truck, and the mirrors are absolutely rock steady. The only downside is that they restrict the wide opening of the doors somewhat.
Overhead on the T660 was the sunroof/ventilator, an exclusive feature on KW and one well worth spec'ing.
Storage around the cab is adequate with door pockets, a glovebox and header rail bins. Up there, too, is a slide-out drawer for a CB, much more elegant than the strap-it-to-the-dash mountings of old. Under the dash is Kenworth's signature log-book stowage.
Another Kenworth feature is the footwell illumination with red light. Overhead lighting is good, and it's done with LEDs to conserve energy in the overnight periods.
The seating is proprietary Kenworth, with comfortable bolsters and a wide range of adjustments. A particularly neat feature is the way the armrests can be folded back behind the seat to open up the walkthrough into the sleeper.
The Sleeper
The sleeper nicely matches the diamond-pleat-but-modern look of the cab. Two full-length closets are wedge shaped to allow for seat back recline without compromising space too much. Above are shelves, one for a TV on the passenger side. The fridge sits on the passenger side, with a two-drawer unit facing on the other. Mid cabinets provide more storage, with a flip-out writing/meal surface on the passenger side.
Under-bunk storage is somewhat limited by the Clean Power installation, though the two baggage compartments are still available.
Upper and lower bunks were spec'ed on this 72-inch sleeper and we could imagine how a team might fairly easily find enough space for their gear, though the floor area seems small after all the 80-plus-inch sleepers we've enjoyed recently.
The sleeper is airy and bright during the daytime, thanks to large side windows and upper vent windows that open without the benefit of hinges. The glass deflects sufficiently to allow for the ventilation. At night, the LED overhead and reading lamps provide plenty of illumination.
I didn't try the bunk, though Park disappeared back there during my driving stint, promptly dropping off to sleep.
On The Road
On the road on Day 1, I took the truck down I-5 from junction 230 just north of Mt. Vernon to 215, pulling a relatively short grade a mile or so from the turn. It was not marked, but I guess it was a 5 percent or 6 percent grade and it brought the loaded truck back down a gear. However, with cruise control set at 55 mph, we crested the grade at 52, only being passed by unloaded trucks and four-wheelers.
On the road, the performance was extremely good, with the transmission and the engine interacting well, and as a driver, I was pretty much oblivious of the gearshifting activity. It just did it for us. And that was how it was to be on our drive the following day, with the relatively narrow two-lane rising and falling through some spectacular scenery and the transmission picking the gears according to the position of the accelerator.
The situation was not so happy in the low side of the transmission, though. Pulling away was a chore because the sharp throttle response would torque the drivetrain and chassis, then the shift would cut fuel then reapply too much too fast after the shift, retorquing the whole setup again. Even feathering the throttle didn't do a whole lot to smooth out the progress through the bottom four gears, so Jim and I took to using the upshift button and the softest throttle to try and tame the savage beast.
Maybe more familiarity would ease the situation, but I don't know. What I do know is that there were a load of major torque reversals through the driveline every time we started out.
And backing under a trailer was exciting. With the UltraShift's centrifugal clutch, you need more than a handful of rpms to get the truck to move. Teasing back under a trailer is not on. You just have to goose it and then the tractor slams into the kingpin. Ouch. And the Jost fifth wheel on the T660 was not user-friendly when dropping a trailer. It's a very tough lift-and-pull to disengage the lock that really strained my shoulder. Ouch again.
The loaded test trailer had a Meritor parallelogram suspension that rides well and that complemented the tractor AG380, which lived up to my every expectation. The T660 rode beautifully and allowed for some spirited driving, maintaining a flat attitude through curves with none of the turn-in some air suspensions show.
As with the earlier T6, the 660 wheelcut is good, aiding both maneuvering and on-road driving around the tight roads of Whidby Island. And, as always, the controls had that Kenworth feeling of being well engineered and well connected so the truck feels like an extension of the driver.
Impressive, too, were the sound level readings: cruising 71 dB is excellent, and even pushing as hard as possible (full power in the gear that gives 45 mph at 75 percent rated speed), the noise level rose to only 74 dB. However, there were a few booming points where the cab vibrations at certain rpms bring up the noise a couple of dB.
Operational Factors
The combination of short driving loops the first day and the nature of the route on the second day saw the active regeneration of the DPF twice during our longer run. It's no big event, but it does bring the light on in the tachometer. There's nothing to do, but drivers are going to need educating that this warning light needs no action on their part.
Access around the truck is excellent, with good steps up into the cab or onto the deckplate behind. The battery boxes for the Clean Power option provide a wide deck.
The new hood incorporates an anti-blow-down feature for safety.
We didn't run at night, but the new lighting is touted to offer 30 percent or more available light, with discharge lighting as an option. Operationally, the much longer life for the headlamps is a big plus for the new model.
Conclusion
We didn't spend as long as we would have liked with the truck – we'll likely go around again in another test and this time make sure we overnight in the sleeper. I'd really like to see how user-friendly the Clean Power system is and how well it performs.
But we had the truck long enough to confirm it is a worthy replacement for the T600. It's quieter, it's more fully featured. It's more comfortable.
And it's very, very stylish.
| Vehicle Specs |
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Tractor Kenworth T660
Frame 10 5/8 rails, steel crossmembers, 285-336-inch OAL
Engine Cummins ISX-500 - 500hp @ 2,000 rpm, 1,650 lbs.-ft. @ 1,200 rpm
Clutch Automatic centrifugal
Transmission Eaton RTLO-16913L-DM3 UltraShift LHP Auto
Drive Axles 40,000# Dana DSP40
Axle Ratio 3.55 to one
Rear Suspension Kenworth AG380 38,000# 52-inch spread
Front Axle Dana-Spicer E1202I 12,000#
Front Suspension Parabolic Taper Leaf 12,000#
Steering TRW TAS65
Foundation Brakes
Front Bendix discs
Rear Bendix Cast drum 16.5 x 7 drum with MGM park on rear
Wheels Polished Kenworth Alcoa Dura-Bright 8.25 x 22.5
Tires
Front Bridgestone 295/75R22.5 R287
Rear Bridgestone 295/75R22.5 M720FE
Fifth Wheel Jost Air Slide JSK37UWL
Fuel Tanks Dual 24.5-inch 120-gallon aluminum
Cab Kenworth B-Cab
Hood Fiberglass tilt, 3-piece 131-inch BBC aluminum w/polished crown
Cab Aero Options Aero hood & bumper, chassis fairings, roof fairing and extenders, aero mirrors
Cab Interior Trim Diamond VIT
Seats K Air Cushion Premium Plus Highback
Sleeper 72-inch AeroCab Aerodyne
Paint Silver Pearl
Additional Equipment
Kenworth Clean Power system; dual high intensity discharge (HID) headlamps; Kenworth GPS Navigation system, multi-function highline display; Kenworth QuietCab package; 2 Paccar 2000cca batteries; Leece-Neville 185-amp alternator; Paccar 105P 12-volt starter; Bendix 6S/6M with automatic traction control and electronic stability program (ESP); 1.87 CFM Cummins air compressor; silicone coolant hoses; low voltage disconnect; Bendix AD-IS air dryer; horizontal back of cab muffler/diesel particulate filter with single vertical, 48-inch curved and polished chrome tailpipe; Intebrake, Kenworth AM/FM/CD radio w/Sirius module; remote keyless entry; Kenworth DayLite doors w/passenger (RH) peeper window; instrument panel with wood grain trim; black rubber floor mat; accessory power outlets in center console; under-dash floor lighting with red lens; Kenworth 18-inch 4-spoke leather steering wheel; adjustable steering column w/telescoping tilt
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Dimensions
Length Not Measured
Width NM
Height NM
Wheelbase 226
Step Heights NM
Floor height NM
Baggage liftover NM
Frame ht @ fifth wheel NM
In Cab
Shoulder width 66
Windshield width 57.5
Height at standup point 60
Seat to ceiling 39-46
Belly room 8-19.5
Legroom
(driver) 14-19
(passenger) 1-19
Footwell width driver/passenger 27.5/16
Sleeper
Walkthrough seats 8 (14 with armrests folded)
Width 84
Height at bunk 85
Bunk to ceiling 58/27
Bunk width 42/27
Clear floorspace 43x50
Measurements
Turning circle
Left 74.25'
Right 77.33'
Closest sight to ground 20.33'
Noise at idle 59 dB (A)
Cruise 71
max accel 74
Jake 74
RPM @ 60 mph top gear 1250
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Drive Test continued...
