Dyno runs with the stock truck revealed the HD was putting down 255 hp at the rear wheels. Torque in stock form was measured at 296.4 lb-ft at the rear wheels, and the exhaust note of the stock system was really quite wimpy. For such a big, bad truck, the HD definitely did not roar like a lion. Not until the MagnaFlow muffler was installed, that is.
After installing the new system, the first thing we noticed was a low, mellow growl of an exhaust note. Not too loud, but definitely enough of a throaty hum to let you know the system was in place. Decibel testing showed the truck jumped up only 8 dBs at idle, from 66 dB to 74 dB. Inside the truck cab at cruise speeds, the dB meter only showed one or two dB more than stock, with the Fourth gear
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measurement going form 68 dB stock to 69 dB with the MagnaFlow components in place.
Back on the dyno with the MagnaFlow parts in place, our HD showed some real performance gains. The 6.0L was now putting 273.5 horsepower to the rear wheels for a gain of 16 horsepower. The torque output was up by 30 lb-ft at 326.9 lb-ft at the rear wheels. With numbers like those, you can feel the performance on the street just as easily as they are read on a page. With the characteristics of easy installation, great sound, and improved power, the MagnaFlow system gets a perfect scorecard. And as good as the stock Chevy HD is, MagnaFlow proved it is quite possible to make a good thing nearly perfect.
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3. We chose to cut the factory pipes just ahead of the trash can-size stock muffler.
6. Band clamps are used instead of welds to connect the MagnaFlow system. The clamps have proven easy to install and very reliable on other trucks we have tested.
7. For simplicity, the huge MagnaFlow 4-inch exit tube attaches in the stock location using the factory hangers.
4. The MagnaFlow muffler is a straight-through design unit that occupies far less space than the stock muffler.
5. The dual MagnaFlow 3-inch inlet pipes fit over the factory tubes just behind the catalytic converter.