This 357, which I borrowed at Peterbilt's headquarters in Denton, Texas, had the newly available setback front axle, which is preferable to the axle-forward design in many axle-weight states. It also had the more steeply sloped hood introduced early in '03 and which I wrote about at the time. The truck was fueled and ready to go with a load of gravel. This let the engine stretch its muscles and kept me busy rowing through the Eaton Fuller "LL" 8-speed.
The set-back front axle sits 47 inches behind the front bumper, or 17.3 inches more than the forward-set version, putting the steer axle closer to the payload and letting it shoulder more weight. It also shortens the wheelbase by the same amount (assuming the same cab-to-rear-axle dimension), which allows a turning radius 2.8 feet shorter, according to engineers' measurements. You still have to spin the steering wheel fast as soon as you begin "bending" a city corner or you'll not make the turn, and an embarrassing back-up is required. I did that only once.
In Caterpillar's lineup, the 12.5-liter ACERT C13 replaces the 11.9-liter C-12, one of Cat's most popular vocational engines. Both the old and new models combine hefty output with moderate weight, which is important to payload. Top advertised horsepower of both the C-12 and C13 is 430, and each makes an extra 15 hp, or 445 max, at 1,600 rpm—a good reason to upshift well before the 2,100-rpm redline. The C13's extra 0.6 liter (36.6 cubic inches) of displacement allows better air flow to help meet increasingly tight exhaust emissions requirements.
ACERT (for advanced combustion emissions reduction technology) uses sophisticated electronics, high-pressure fuel injection and, in larger engines, double turbocharging. It does not use exhaust-gas recirculation, but has a water-to-air cooler between the turbos and the air-to-air cooler. The two turbos are the most visible hardware change on the 13, which otherwise looks much like a 12. The turbos are in series, meaning one ahead of the other in the exhaust stream.
Together the high- and low-pressure turbos compress and push a lot of air, and there was a pronounced whistling as air was drawn through the intake system. I found it entertaining, but it's not characteristic of the configuration, said Bob Keene at Cat's Mossville, Ill., offices. He guessed it had to do with the air plumbing or perhaps the air cleaner design on the Pete.
What a C13 should do is pull more strongly at low revs, Keene said, and this would be noticeable on a long, hard upgrade. There aren't many such hills in North Texas, but this engine certainly lugged nicely. Maximum torque is 1,650 pounds-feet at 1,200 rpm, but I could drop it to 1,100 and less, and it would pick right up with no shuddering or vibration. So the C13 is a worthy successor to the -12, with or without the whistle.
