Modern Steel, Retro Feel

The C15, retaining a familiar response amid new technology, offers a lot more than new skin on an old Cat.

Caterpillar loyalists will be happy to know that the new C15, using the company’s ACERT technology for emissions reduction, has lost no power. Coupled with an Eaton Fuller 18-speed, the C15, rated at 550 hp and 1850 pounds-feet of torque, demonstrated in a test drive just how satisfying it is to dial in rpm and maintain road speed when the situation demands – or simply when you want to. Strapped into a two-week-old Peterbilt 379X for a drive in Texas, the C15 provided throttle response and gradability to match the show-truck appearance of Pete’s newest premium model.

Test-driving cooled exhaust gas recirculation engines over the past year, I’ve been struck by the availability of torque and low-end response in all the engines. Cat’s alternative to EGR – Advanced Combustion, Emissions Reduction Technology – is no exception. Whether by design or coincidentally, Cat has created an engine to meet current and future emissions standards while maintaining the sensory qualities of the old C15 power horse.

Unlike EGR engines, the new C15 has a retro feel – in a good way. For drivers accustomed to shifting by engine and turbo sound, nothing has changed. Twin-wastegated turbos, cooled by an intercooler and air charge cooler, provide the satisfying sound of rpm rising and dropping. If drivetrain management is your No. 1 source of satisfaction, you’ll enjoy seeing how much you can get out of the mammoth power available from the C15.

The C15 has excellent gradability, which engineers define as the ability of the engine and powertrain to remain at cruising speed in top gear on a 1 percent grade. The C15 also had no problem with the short 3 percent and 4 percent grades on Highway 35E south of Dallas, losing 3 or 4 mph in 18th and fewer in 17th. Loaded to 75,000 pounds, the Pete passed many of its lumbering brethren on the uphills.

Cat chose the lower-speed turbos over the high-speed turbos of most EGR engines. Cat’s David Shannon, a senior account manager, says twin turbos were picked because the technology existed in Cat off-road engines and because “twin turbos allow for controlled volume of clean intake air, not exhaust gas. Twins promote more complete burn and increased fuel economy with increased boost.” Besides, the turbo no longer needs to be replaced if the waste gate goes belly-up.

Partner Insights
Information to advance your business from industry suppliers

The turbo gauge shows a strong, quick boost if you decide to keep your foot in it above 20 pounds pressure. Little is needed to put the boost at 50 pounds. Shannon says boost correlates with fuel consumption, but good fuel economy exists for those inclined to stay within the torque band. That extra boost is there at the top end of your high gears, especially, and is available if you need to grab a lower gear and motivate.

Torque remains constant between 1200 and 1600 rpm. It is possible to accelerate at the low end without bumping it down a notch from 17th, even on those rolling 1 percenters. At the other end, you have more room than Jerome Bettis makes in a defensive line. Top end should be well over 100 mph with 3:55 rears.

In 16th doing 70, my tach showed a mere 1500 rpm – certainly not in the sweet spot but still within the torque band. This engine’s sweet spot is 1350, probably narrower than it used to be. Dialing in the sweet spot will probably save fuel even though you’re dragging that extra gear iron by splitting to stay there. With this engine, the best fuel-saving tactic may be to use direct except in situations when pulling corners torques your tires or on grades where you slip a little below 1350. Cruising in 17th rather than 18th may also save fuel because you don’t need the rpm for speed. At 65, you ought to be sitting right in that sweet spot in 17th. In 18th, you’re flying free and easy.

Twin turbos do not present a maintenance problem, says Shannon. Shaft speeds are 30 percent lower than in the high-performance turbos on most EGR engines. That means increased responsiveness at the top end and longer turbo life, which could be an important distinction for those concerned about the life of the high-speed, high-performance single turbos used on EGR applications. All things being equal, EGR engines may have the edge in acceleration off the line, but the boost at the top end gives the C15 distinct advantages at cruising speed.

Cat chose to waste-gate its turbos on the C15. Waste gates make the engineer’s job easier since they make considerations like altitude and type of application less of an issue. While some argue that waste gates are great around town, line-haul operators may be skeptical because waste gates are known to make pistons work harder at highway speeds.

Some would opt for a larger turbo housing to allow the pistons free play. But if the rest of the Cat ACERT system is working, the waste gate’s supposed shortcomings might well be nullified. It is likely that non-waste-gated twin turbos rated 550 would be much bulkier and more expensive. As compromises go, the waste gate is a good one on this engine.

After air intake and charging in both turbos, the intercooler cools the air before it gets to the second turbo, sending the excess heat to the water side. The air charge cooler provides a final ice before the air is sent to the cylinder.

There the injection event is shaped by electronically controlled air flow, timing and fuel availability. Pilot injection allows a spark to ignite the fuel-air mixture. This single-injection event includes multiple injections of fuel and multiple firings. Shannon says this allows for more complete burning of fuel at lower temps, which allows nitrous oxide and particulates to be lowered at the same time. Plenty of cool air from those twin turbos helps make this happen.

Cat’s proprietary electronic control unit “understands every function and position of the engine during each firing cycle,” says Cat literature. It also takes into account things such as intake air temperature, atmospheric pressure and coolant temperature. It makes possible Cat’s claim that fuel mileage remains the same or is slightly better than pre-October 2002 Cat engines.

Cat customers likely will not be able to tell the difference between this engine and its forebear except that they will hear and feel the extra turbo boost. It does not appear that it will be more expensive to maintain. As befits a modern retro giant, oil change intervals remain the same at 30,000 miles. The C15 will also lubricate on CH-4 oils, which cost less than the newer CI-4.

If the C15 proves to be as dependable as its forebears, Cat should be able to recoup the time and money it spent by abandoning EGR and developing its own technology, particularly since the engine is certified for 2004 already.


Peterbilt’s 379X is a magnet for drivers, some of whom drive trucks that look wonderful – until you park this Pete beside them. There is more chrome on this limited edition truck than any production truck I can imagine. Polished aluminum fenders, matching punched oval grille and air cleaner and a polished aluminum accent that runs stem to stern in the middle of the hood will not be dimmed by the darkest days.

Peterbilt dealers have heard about the truck’s power to turn heads, says Peterbilt General Manager Dan Sobic. Owners say things like, “You can’t believe the looks I get” and “The CB chatter is phenomenal,” Sobic says.

Inside, the brushed aluminum dash and the chrome gear shift lever, knob and base plate carry through the heavy metal accent Peterbilt has used to upgrade its classic 379. In the bunk, the same brushed aluminum is used as trim and provides a striking contrast to the dark charcoal cabinetry. The ergonomically advanced leather seats are comfortable and infinitely adjustable.

Based on a 300-mile test drive from Denton to Waco, Texas, and back, Cat’s new C15 rated at 550 hp turns this beautiful machine into something akin to Catherine Zeta Jones with a black belt. The rock-solid 379X has excellent wheel cut and visibility to the rear, features missing in some big iron. As with the regular Model 379, that wheel cut will get you in and out of some very tight quarters, though front visibility limits how easily you can gauge your steer tires’ position relative to the curb. The hood is big, but you can actually see the crosswalk when you stop for that red light if you don’t inch too close.

One final point: Buying this truck means budgeting time to clean and polish it. You owe it to yourself – not to mention your jealous peers on the road.