Nothing shakes the customers up more than change. Cummins has steered clear of change with its ’07 lineup, making only subtle modifications to the engine itself. You’ll find a bit of new hardware hanging off — and behind — the engine, and some new ECM programming, but really, the red engines for ’07 seem to be more of an evolution than a revolution.

Cummins is hanging its corporate hat on the fact that 2007 offerings are not substantially different from earlier models. When the Columbus, Ind.-based engine maker launched its 2002 EPA-compliant ISX engines, they came with an uptime guarantee. Cummins saw only a handful of claims over the term of the promise, so with few modifications to the engine itself, Cummins is pretty confident that the ’07 roll-out will go just as smoothly.

Today’s Trucking got a sneak preview of the company’s ’07 engines this past spring (2006) — an ISX and an ISM — and we’re inclined to agree with Cummins’ guarantee they’re road ready.

Building on the 2002 platform, Cummins has been working extensively with the new sub-systems for ’07, namely, the exhaust aftertreatment system; a.k.a. the diesel particulate filter (DPF), a new electronic controller for the Holset Variable Geometry Turbocharger (VGT), and expanded memory and processing power for the ECM.

Hardware modifications include a redesigned EGR valve and EGR cooler, and a coalescing filter to soak up the crankcase gasses. And that’s about it.

Development of the ’07 product began in September 2000 — six years before production. By February ’02, Cummins had decided on cooled EGR, after looking at several different technologies.

“In making the down-select to cooled-EGR, we focused on the total cost of ownership to the end user,” says Steve Charlton, Cummins’ executive engineer.

Computer-based design and engineering work allowed Cummins’ engineers to focus on virtual prototyping to look at stresses, fuel economy, emissions, and performance without committing to expensive tooling. They didn’t even build a working prototype until February 2005. Those Alpha engines spent many thousands of hours in the test cells before they hit the road in May 2005. Since then, they’ve accumulated 2.5 million miles across the product line.

Cummins is in what it calls the RAPid phase of testing now (Reliability, Assurance & Problem identification). They’re running tests in various applications and duty cycles and soliciting customer feedback. “We’re looking at limited production by September of 2006, and full production by end of the year,” Charlton says.

On-going Evaluation

A small fleet of trucks are running 20 hours a day in two shifts over a short course of about 125 miles near the test center in Columbus, Ind., designed to challenge both the engine and the aftertreatment system. Trucks are exposed to a mix of two-lane roads, urban stop-and-go conditions, and a few steep grades. The trucks run five days a week, and are left idling all weekend long (52 hours at a stretch) to load up the DPF with soot.

The test route wouldn’t seem grueling to an untrained eye, as most of what one might expect in testing a truck engine has already been done. High-speed operation and long hard pulls actually help with particulate filter regeneration, so Cummins is testing them under less than ideal conditions.

Back in 2001-2002, the engine makers were interested in durability testing. This time around, they’re refining the aftertreatment system, which requires light loads, stop-and-go traffic, and modest speeds. That’s where the engine runs cool, producing the least amount of heat. Since high exhaust temps are required for the passive regeneration of the particulate filter, this course was designed to load the filter up with soot as often as possible, while still giving the engine a bit of a workout.

Steering & Gearing

The truck I drove came from Cummins’ test fleet. It was an early-build International ProStar with a 13-speed transmission loaded to 75,380 lb. Under the hood was a 500-hp ’07 ISX boasting 1,850 lb-ft of torque.

The first obvious difference between the ’07 and the ’02 engines is the throttle response. Current users will be aware that upon applying a little throttle from a stand still, the engine just lights up. That’s the VGT at work. The ’07 has a tamer VGT, thanks to an electric controller. But that doesn’t mean it’s lazy. The turbo spools up more slowly, meaning there’s a more gentle ramp-up of the power, making it a bit easier to shift.

When you give it throttle up in the higher gears, you can watch and feel the boost pressure climb, and it comes on like gangbusters: 0-45 psi in about three seconds. That’s motivation. And quick recovery after an upshift.

The DPF plays into how the engine feels too. I’m told it creates a higher level of back pressure than before, and that tends to bring the revs down pretty quickly between shifts. That means you’ll have to shift more quickly. The upside is you lose less road speed between gears giving you faster overall acceleration.

While I haven’t seen the torque and power curves for the engine yet, the torque curve feels noticeable flatter — a fact confirmed by Mario Sanchez, Cummins’ heavy-duty product manager. What the driver feels is less of a droop in the “pulling power” as the revs fall while climbing a hill. The engine feels distinctly stronger, which will please drivers to no end.

If you’re running at the recommended 1,450-1,500 rpm, you have a comfortable margin between cruise and peak torque, and 1,200 rpm isn’t the end of the world. I lugged it down to 900 rpm on one hill, and it was still pulling. Didn’t keep it there for long; just wanted to see what happened.

Coolant temps remained low, I thought, for most of the trip, averaging below 180 F. We hit 210 on a couple of low-speed climbs, yet I couldn’t hear the fan roaring away. That’s a testament to the variable speed fan drive. It’s always on to some degree, but turning at a speed appropriate to the demand.

We didn’t get into fuel economy, and at the time Cummins was not yet certain what indicators they might use to advise the driver of an active regeneration event, so I’m not sure if we experienced one or not on the trip, though Charlton says it’s unlikely.

My seat-of-the-pants impression of the ’07 ISX is that it’s a better engine than its predecessor: more refined and just as capable –mostly a product of the new turbo controller. I believe drivers will be pretty happy with how it feels and pulls, and all the other numbers Cummins is throwing around the marketing literature — oil change intervals and the like — suggest it’ll be business as usual when we tear December 2006 off the calendar.