When we last left you, we had added a free-flowing cold-air intake and mass airflow sensor (MAF) on our '02 Chevy truck. Well, now we can get air into the engine, but that stock exhaust is a bit restrictive. To get rid of some back pressure and add additional horsepower we called on the pros at Magnaflow to set us up with the appropriate exhaust system for our daily driven truck. Magnaflow's solution came in the form of an after-cat system built entirely of stainless steel. For that added "bling," the muffler is even polished! Well, that won't give us any additional horsepower, but it sure looks great, and with the polished stainless steel tip it will provide us with an exhaust system that is very corrosion resistant and that will possibly outlast the truck.
Our first step was to strap our truck down on the Dynojet 248 and get a baseline, so we were off to the Primedia Tech Center where we produced a base 228.1 SAE corrected horsepower, with 276.5 lb-ft of torque. Satisfied with a reliable and consistent baseline, it was onto our Autolifters lift, where we started removing our old, restrictive stock exhaust. This is a simple job that is much easier on a lift but can be performed in your driveway. We started by unbolting the fasteners that go into the catalytic converter and prying the rubber mounts off the hangers mounted on the original exhaust. Be sure to leave the rubber mounts in place on the truck, as they will be reused. Starting at the front by the catalytic converter, we attached our first pipe, then snaked the rear tailpipe in place and mounted it on the rubber mounts. We did this so we could center the muffler and adjust the pipes so they won't rattle or rub any of our suspension components. When we were satisfied with the fit, we tightened everything and fired up the truck to check for exhaust leaks. Since the Magnaflow kit fits so well, we weren't shocked to find we had a nicely sealed system, with no leaks.
The exhaust note was considerably deeper, yet not obnoxious-very tolerable, even on a long trip. We figured it was time to see proof in numbers, so we strapped it back on the Dynojet. After three pulls, we came up with a best of 235.8 SAE corrected horsepower, with 281.2 lb-ft of torque; that's a 7hp gain and a 5-lb-ft gain in torque. Keep in mind these numbers reflect three runs of testing, and there is still more we can do to our truck to pick up some valuable horsepower and torque. However, for now, this makes our truck sound great and perform equally as well. Follow along and see how 30 minutes of work and one Magnaflow after-cat system can gain a few ponies and make that Chevy engine roar.