Mission accomplished

In its state-of-the-art testing cells, Cummins subjects the ISX to every imaginable working condition while powerful computers gather and analyze a wealth of data.

After driving Cummins ISX and ISM engines, an Overdrive equipment editor finds them tooled to perform at least as WELL as previous models.Cummins’ leading 2007 heavy-duty engines have retained their foundational components and, not surprisingly, the same look.

“It will be hard to tell the ’07 engines from the ’06 engines by appearance,” says Mario Sanchez, Cummins’ marketing manager for new products. The only visible changes on the ISX are a crankcase breather housing and an exhaust recirculation line on the driver’s side, and a cooling tube and an electric motor for the variable geometry turbocharger on the passenger side. On the ISM, only the crankcase breather and the VGT’s electric motor are visible.

“The basic engines have not changed,” Sanchez says. “They have the same block, head, crankshaft, pistons, fuel system, turbocharger, connecting rods, camshafts, gears and flywheels.”

Cummins’ latest technology, like its current design, is centered on its VGT, which controls the flow of gases through the engine and is critical to effective exhaust gas recirculation. Also key to the design is the diesel particulate filter, which will be used on all 2007 engines. It removes soot and ash from the exhaust.

In strenuous use, the engines run hot enough to passively clean the DPF. For lighter work when the engine runs cooler, misted diesel fuel injected upstream of the filter creates the heat necessary for cleaning. The ash that collects in the filter is vacuumed out every 200,000 to 400,000 miles, depending on application.

One big change is increased power and torque for both engines. Cummins now has a 600 horsepower, 1,850 lb-ft. torque ISX; also 425 and 485 horsepower ISX models with SmartTorque technology that gives them 1,750 lb.-ft. and 1,850 lb.-ft. of torque, respectively. Also newly available are 410 and 425 horsepower ISMs with torque up to 1,550 lb.-ft.

I experienced their performance when I came to Cummins’ Columbus, Ind., test center. The first vehicle: a 2003 Volvo 770 condo with a 2007 ISX rated at 500 hp and 1,850 lb.-ft. of torque, an Eaton 18-speed double-over and 3.73 rears. We hauled a loaded 53-foot van. The DPF was vertically mounted behind the cab.

Our 100-mile test drive included city and rural driving on two- and four-lane roads, including some challenging hills. Outside town we encountered 3 percent and 4 percent hills, some a half-mile long. I braked hard on the descents and started each climb in high gear at about 1,250 rpm and 50 to 55 mph – no momentum, just muscle. This isn’t the manufacturer’s recommended procedure, but it truly tests an engine’s power.

The ISX easily cooperated, and no hill required downshifting until we reached the longer, steeper inclines near Lake Monroe and up Kelly Hill. The ISX pulled as strongly as any 500-hp diesel.

We crept down the narrow, curvy, 6 percent drop to Lake Monroe northbound on Indiana Highway

KEY SPECS AS TESTED
ISX Engine ISM
500 Horsepower 410
1,850 Torque 1,550
2003 Volvo 770 Truck 2005 Kenworth T600
53-foot van Trailer 40-foot drop-deck flatbed
77,000 pounds GVW 59,500 pounds
RTLO-187 18B, 18 speed Eaton Transmission RTO16910C-DM3, Eaton Autoshift 10 speed
3.73 Rear Axle 3

446. Then we tackled the mile-long, equally steep climb back up. I stayed in high gear as long as possible, but about 100 yards from the top we got down below 1,100 rpm, so I grabbed 17th.

A few miles farther, Kelly Hill’s 8 percent half-mile incline surprised me, just west of Nashville, Ind., on Highway 46: steep, with considerable traffic. We were below 55 mph at the bottom, and one look at that hill told me we’d be downshifting. The engine didn’t clear the hill in a single bound, but the company says it will pull heavy loads up hills as effectively as its ancestors. This ISX did so with our 38.5 tons.

Cummins officials say their ISX and ISM tests show equal or slightly better fuel efficiency compared to current engines. They predict a 6.5 mile-per-gallon average but realistically expect closer to 7. Their test also indicates improved reliability and durability and the same oil-change intervals.

I next climbed into a 2005 Kenworth T600 with a 410-hp ISM and 1,550 lb.-ft. of torque, an Eaton 10-speed automatic and 3.90 rears. We drove the same route, hauling a loaded 40-foot drop-deck.

The engine’s power coupled with Eaton’s 10-speed automatic made this drive too easy. The ISM was as responsive and sure as any 410-hp engine hauling almost 30 tons up 6 percent and 8 percent grades. It never lagged or showed a shortage of power.

To more thoroughly test power and torque, I locked in high gear at the beginning of the test and started the 3 percent and 4 percent climbs just south of town at about 1,250 rpm at 50 to 55 mph. In high gear, the ISM pulled its load up all hills without strain. When I let it, the truck dropped from high gear only twice: climbing from the lake and climbing Kelly Hill.

These two tests showed that Cummins was not deterred by the 2007 emissions standards handed down by the Environmental Protection Agency and the California Air Resources Board.

“I like the idea of clean air,” says Glen Haegele, a Cummins technical adviser. “Just give me a reasonable target and time to get there, and let’s go for it.”

Cummins has met its goals of satisfying emissions requirements while maintaining or improving performance, fuel mileage and reliability. These two engines pulled just as hard and steady as their Cummins predecessors or any equally rated heavy-duty diesels, if not more so.

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