Don't worry, drivers, say many American engine makers. Our '07 diesels will perform just like now, and you probably won't even know you've got one under the hood. Those filters on the exhaust system won't affect power one bit, and you won't notice it's working. All will be well.

That's essentially the message from Detroit Diesel, except that it expects the driving experience of upcoming Series 60 models to be even better, thanks to new hardware and software. To prove it, Detroit executives recently held a ride-and-drive event at the home of corporate parent Freightliner Group in Portland, Ore., so reporters could feel for themselves how the engines act.

Led by Tim Tindall, '07 project manager, they also described their extensive S60 test program, which is now well under way and will cover the equivalent of some 14.8 million miles before the engines come out this January. Like other builders, Detroit is putting its engines through a rigorous and methodical program using dynamometer and road running, interspaced by detailed evaluations and engineering improvements, to ensure they will hold up in real life.

Engineers know that there were disappointments with products fielded back in October '02, which use much of the same hardware and electronic control apparatus that will carry through on the '07 models. So test miles on the new engines will be five times those that the previous models went through. Because Detroits are now available only in Freightliner-family trucks, including Sterlings and Western Stars, engineers are working closely with Freightliner's test staff in Portland. They say the integrated approach to marrying a diesel with a chassis results in more information sharing and therefore greater precision for the match.

Work with Freightliner on the '07 engines began in early 2003, noted Elmar Boeckenhoff, Freightliner's director of engineering, that will encompass nearly four years by the time the engines go into production. A similar program is under way for MBE diesels, though the subject of this event was the Series 60.

Of course most of us looked forward to the driving, which came immediately after the briefing. Only two editors present had CDLs and were able to drive, and I was pleased to have Tindell, the project manager, as my rider, because he was able to explain the workings of the Series 60 and answered my many questions as I drove.

A small fleet of test rigs waited outside, and each tractor packed a 14-liter 455-horsepower Series 60 and pulled a 53-foot Utility van ballasted to take each close to the 80,000-pound legal maximum. Our tractor was a white Columbia with a 72-inch Raised Roof sleeper destined for Ryder System. We hadn't been in the seats long when the trucks ahead pulled onto the street and began making their way out of the Swan Island area and out of town. I've got a light foot and fell well behind at first, but soon caught up as we headed toward U.S. 26 and the hilly, wooded countryside west of Portland.

SMOOTH – ALMOST TOO SMOOTH

I soon felt at home with both tractor and engine, having driven similar rigs when Detroit was showcasing its then-new '02-04 Series 60s. That was in the Carolinas, almost on the East Coast, and here we were several years later on the West Coast, yet the S60 was rather familiar in both the pleasing growl it emitted and the power it made.

It was smooth – almost too smooth – because gone is that slight push in the pants I felt with the earlier S60s as their variable geometry turbochargers went to work on upgrades. The new turbo uses a sliding nozzle run by electronic controls instead of the older unit's moving vanes and pneumatic controls. The new turbo is more precise and responsive, Tindell said. It works without that little whoosh that I found to be fun, but it includes a powerful retarder that easily held road speed in check on all but the steepest downgrades on this highway.

We climbed a number of stiff upgrades while heading west on 26 and the engine pulled strongly from an indicated 1,200 rpm on up. If I was late in getting on the gas, the S60 dug in and made up time, accelerating authoritatively to 1,900 or so. It made a combination of torque and horsepower, which occurred seamlessly – a management buzzword that I'd never use except it really fits here – all through the operating range.

Tindell later explained that this rating makes a constant 1,550 pounds-feet from 1,100 rpm up to 1,500, and meanwhile horsepower builds toward its 455 peak at 1,800 rpm. Those curves jibed with what I felt in performance. To climb hills better, you usually need horsepower, and downshifting got the engine into a more lively mood, which it was at 1,500 rpm and higher. But it would hang in at lower revs, usually not accelerating but not falling off much, either.

The transmission was an Eaton Fuller 10-speed with a "C" gear set, which has rather widely spaced ratios, especially in high range. Ninth gear was good for cruising up to 55 or so mph and I shifted to 10th as we approached 60. Upshifting one gear reduced engine speed by 400 to 500 rpm, but the engine was strong enough to take it.

One point of this drive was to show that the aftertreatment device on the exhaust did nothing to choke the engine or limit power. It didn't. Tindell and his colleagues also wanted to show that the driver feels nothing as the diesel particulate filter inside the device goes through an active regeneration – that's when it burns off soot with the help of a little fuel injected into the exhaust stream. The fuel mist is heated by the oxygen catalyst and then enters the DPF, causing the regeneration.

Indeed, there was no loss of power as the high-heat light illuminated on the instrument panel. If not for that – and the readouts of increased temperatures on the screen of the laptop computer resting on the dash in front of Tindell – I'd never have known anything was happening in the DPF. Normal temps inside the can were 400 to 500 degrees Centigrade (752 to 932 degrees Fahrenheit), while regeneration readouts showed 650 C (1,202 F) "in," at the front of the DPF, and 660 to 670 C (about 1,230 F) "out," at its outlet. That's hot, for sure, but those temps are needed to burn the particulates out of the filter.

Exhaust-gas temperature at the tip of the stack is a little less, Tindell said, and heat dissipates quickly as gas is dispersed into the atmosphere. Still, care must be taken to keep the stack far enough from a van trailer to avoid burning its paint or damaging a reefer unit.

Regeneration went on for maybe half the 63 miles of our westward route. It would've been done quicker, except the system interrupted the process whenever the exhaust brake activated. This happened whenever I took my foot off the accelerator. If I had switched off the brake, interruptions would've been fewer. Applying the service brakes doesn't affect regeneration, Tindell explained.

ACTIVE REGENERATION

As you'd expect, active regeneration starts as needed, but it only works on Detroits if the truck is moving. It activates at 20 mph or higher, and stops when speed drops to 10 mph – speed points that might be changed between now and January. This prevents anyone from being hurt by hot exhaust gas (it's so clean you could almost say hot air) or from heat radiated off exhaust parts. The aftertreatment device, including the DPF, is under the sleeper at the tractor's right side, and is not reachable unless you're under the truck.

Speaking of heat, it's worth noting that Detroit and Freightliner will use bigger radiators to handle greater rejection of heat from the '07 engines. This Century's radiator had a core with 1,625 square inches, compared to the 1,350-square-inch core now used. The bigger radiator is not apparent from outside the truck. And it seemed to work, because the needle in the temp gauge on the dash never moved much and no alarms sounded.

About that high-heat light on the instrument panel: This has a new symbol, a little thermometer and a wavy vertical line with other lines radiating toward a little can. This light might be standard or an option, and its color will probably be amber instead of the red on this truck. Red signals an alarm and might scare a driver into shutting down, Tindell said.

Scenery along U.S. 26 is a pleasant mixture of hills and gullies, with streams crossing beneath stoutly built bridges. As we got close to our destination, there was evidence of logging activity, and logging trucks passed by regularly. It was a nice trip, and too soon we got to where we had to stop, at Camp 18, a rustic restaurant and outdoor logging museum with equipment displayed around the premises. Included are steam donkey engines, big saws, and locomotives and rail rolling stock, but none of the trucks that put logging railroads out of business. Trucks just don't generate nostalgia with the public, I guess.

Twenty-five or 50 years from now, will rigs like this Freightliner and its clean-burning diesel with quaint (maybe by then) exhaust-cleansing apparatus generate nostalgia among trucking people? Could be. For now, they're just the latest in a heroic effort to clean the air while still moving freight.