As much as we might like the sound and the fury of a big, open exhaust on our diesel engines, does it necessarily flow better than a high-performance aftermarket system? Sure, a big, bad diesel rumble announces your arrival with authority. On a long haul, though, that heavy drone from open pipes can drive you batty, not to mention add to driver fatigue. So we wanted to know if it is possible to have a relatively quiet exhaust that still performs well? Or maybe even better?
To get to the bottom of these issues, we decided to do some before-and-after testing on a '96 Dodge Ram with a 12-valve Cummins. The vehicle already had a custom-fabricated open exhaust on it with no muffler or catalytic converter. At first glance, that might seem to be the ideal setup for maximizing performance.
 Stock Downpipe The factory...  Stock Downpipe
The factory downpipe was the first thing to go. |  4-inch Downpipe The new Banks...  4-inch Downpipe
The new Banks mandrel-bent system starts with a fresh downpipe measuring 4 inches in diameter. |  No Muffler = Noisy Drone ...  No Muffler = Noisy Drone
Basically, the only muffler in our old system was the turbocharger itself! |
This particular system looked like it had been slapped together by a cross-eyed blacksmith. The tubing was of varying sizes, approximately 3 inches in overall diameter at best, and poorly bent with pinches and welded seams that cause turbulence and restrictions. Also, the Y-section did not allow for a smooth transition to the dual rear pipes and displayed several leaks.
 4-Inch Free-Flow Muffler ...  4-Inch Free-Flow Muffler
This Banks Monster Muffler flow-through unit features an internal expansion chamber that dissipates the irritating midrange drone of an un-muffled exhaust. |  With the old open-exhaust...  With the old open-exhaust system removed from the chassis, various constrictions and restrictions in the tubing became even more obvious. The dual tailpipes were of different sizes, one using several reducers to a 2 1/2-inch outside-diameter pipe. Also, the system was not stainless steel, and corrosion was evident along with several notable exhaust leaks. |  The Banks designed Y-pipe...  The Banks designed Y-pipe (left) is designed to reduce restriction and promote increased flow over multi-piece, welded Y-pipe junctions. Note the obvious difference in size as well. |
Banks Power took one look at this funky, rusty, old plumbing and felt pity for us, offering to replace it with a smooth, mandrel-bent system measuring 4 inches in diameter and outfitted with the its straight-through Monster Muffler. It's claimed to more than double the flow of the stock muffler (which was absent on this particular truck). Also, the Banks unit features an exclusive expansion chamber that dissipates the irritating midrange drone that can plague other straight-through mufflers (and our open exhaust, for that matter). We were hoping that would be the case, but Banks went the extra mile and backed up its claims with some hard numbers.
At the rear of the system is a Banks seamless Y-pipe along with dual 3 1/2-inch 409 stainless tailpipes that include Banks' weld-on 5x6-inch 304 polished stainless tips. The 3 1/2-inch dual tailpipes open the way for the exhaust to zip through, increasing the flow area 52 percent over a single 4-inch tailpipe, according to Banks.
After checking out both the power output and sound levels, frankly, we were surprised by the results. Not only did the Banks system substantially quiet down the exhaust note, we gained power at the same time!