Going With The Flow
MagnaFlow's New After-Cat Exhaust Adds 12 Peak Horsepower To The Rear Wheels Of An '03 5.3L Chevy Silverado

Text and Photography By: Joe Pettitt

   Installing an after-cat exhaust system is one of the best first-engine-modifications to make. A free-flowing exhaust offers the potential to make additional power relatively inexpensively and provides the additional benefit of a performance-tuned exhaust note. It's not a question of if you should do it, it's a question of which system should you install.

   While there are dozens of systems to chose from, each with its own appeal and sound quality, after installing and testing MagnaFlow's new after-cat unit on an '03 Chevy Silverado, we recommend you put MagnaFlow on your shopping list and do some serious comparisons with other brands before you make your final decision. We think you'll find the MagnaFlow system a tough competitor and a part worth installing on your sport truck.

   Here's what MagnaFlow's new system has to offer in addition to making a few extra ponies. All of MagnaFlow's after-cat systems are fabricated from 16-gauge, 430-series stainless steel. The tubing is mandrel bent - a process that does not create the restrictions seen in press - bent tubing - to promote maximum exhaust flow. MagnaFlow also prototypes all of its systems on the specific vehicles to ensure the customer receives the best fit and optimum performance from the system. MagnaFlow verifies the performance improvements at a new Research and Development facility with DynoJet and Mustang dynamometers. The company also conducts sound testing to tune the exhaust note and check that sound pressure levels and frequencies are within a comfort range. They make sure the system is neither too loud nor has an annoying resonance or drone.

   The heart of the system, however, is the properly sized MagnaFlow stainless steel muffler. MagnaFlow's mufflers have a free-flowing, perforated, stainless core. No baffles, chambers, or louvers. No restrictions at all, just straight-through, wide-open performance with a smooth, deep tone, and each MagnaFlow stainless muffler has a highly polished mirror finish for a show truck look.

   MagnaFlow's approach to building a better muffler is to fill the unit with high temperature, acoustical suppression material to absorb the harsh frequencies of the exhaust. The material also repels moisture in the fuel, very important for durability because there is, according to MagnaFlow, on average 2-1/2 times more water in gasoline today compared to the '60s. This material resists corrosion and prevents the muffler from rusting from the inside out. The core material is wrapped with stainless steel mesh to provide durability under high temperatures as well as additional sound absorption. The muffler features welded, lap-jointed contacts to avoid distortion and cracking.

   MagnaFlow touts that each system is designed to replace the factory exhaust system from the exit side of the cats, using OEM style hangers for a factory fit, and come with a lifetime warranty on materials and workmanship. It also claims that each system is developed on the dyno to provide a real improvement in power. After installing one of its systems and witnessing a before and after series of dyno tests, we can verify the fit is OEM quality and the finish is about the best on the market. And perhaps most important of all is the system delivered the power to the drive wheels. As for the sound quality of the system, you'll just have to experience it for yourself.

HERE'S THE LAYOUT OF THE STOCK EXHAUST SYSTEM LOOKING TOWARD THE TAIL OF THE TRUCK. USE THIS AS A DESIGN BASELINE FROM WHICH TO COMPARE THE MAGNAFLOW EXHAUST SYSTEM.

HERE'S ANOTHER VIEW OF THE STOCK SYSTEM, DETAILING THE TAILPIPE DESIGN AND POSTITIONING.

IN ADDITION TO BUILDING AN EXCELLENT PRODUCT THAT ACTUALLY PERFORMS AS PROMISED, MAGNAFLOW PROVIDES A GREAT DO-IT-YOURSELF EXPERIENCE AS WELL. THE PRODUCT COMES PACKAGED AND PROTECTED ALMOST AS WELL AS IT IS MADE.

INSTALLING THE MAGNAFLOW AFTER-CAT EXHAUST BEGINS WITH REMOVING THE STOCK EXHAUST. IT'S EASIER TO REMOVE IF YOU CAN SUPPORT THE EXHAUST SYSTEM.

REMOVE THE NUTS FROM THE BOLTS THAT FASTEN THE EXHAUST SYSTEM TO THE EXHAUST MANIFOLD.

NEXT, YOU NEED TO DISCONNECT THE EXHAUST SYSTEM FROM THE HANGERS THAT SUPPORT IT UNDER THE BODY. MAGNAFLOW TECHS SPRAY A LITTLE WD-40 ON THE RUBBER SUPPORTS TO MAKE EXTRACTING THE EXHAUST MOUNTING TANGS EASIER.

THE PROFESSIONALS AT MAGNAFLOW USE A SPECIAL TOOL TO REMOVE THE EXHAUST MOUNTS. IF YOU ARE DOING THIS AT HOME, A SET OF CHANNEL LOC PLIERS OR EQUIVALENT WILL DO THE TRICK.

THE STOCK AFTER-CAT PORTION OF THE EXHAUST SYSTEM COMES OUT IN ONE PIECE. WE TOOK THE OPPORTUNITY TO OFFER A COMPARISON OF THE STOCK UNIT VERSUS THE MAGNAFLOW COMPONENTS. THE MAGNAFLOW EXHAUST IS FAR SUPERIOR TO THE STOCK UNIT.

USING THE SUPPLIED GASKET, FIT THE MAGNAFLOW LEAD PIPE TO THE STOCK FLANGE. INSTALL THE NUTS ON THE MOUNTING BOLTS, BUT DO NOT TIGHTEN. LEAVE THEM SLACK TO PROVIDE SOME MOVEMENT TO MAKE INSTALLING AND MOUNTING THE MUFFLER AND TAILPIPE EASIER.