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.
The factory downpipe was the first thing to go.
4-inch Downpipe The new Banks mandrel-bent system starts with a fresh downpipe measuring
No Muffler = Noisy Drone Basically, the only muffler in our old system was the turbocharg
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 This Banks Monster Muffler flow-through unit features an interna
With the old open-exhaust system removed from the chassis, various constrictions and restr
The Banks designed Y-pipe (left) is designed to reduce restriction and promote increased f
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!
While acceleration and backpressure are fairly simple numbers to measure, analyzing noise levels can get a bit more complicated. That's because sound comes from both the air and vibration (transmitted through solids). Not only that, the location of the driver and the frequency complicate matters. One person's music can be another's annoying noise. What usually matters most to drivers of diesels is how the exhaust sounds in the cabin with the windows rolled up.
In this particular application, the Banks system provided a significant measure of relief, and even gave us a gain in acceleration. The reduction in backpressure also lowered the EGT, as well. All of which is proof positive that it's important to keep an open mind when considering open pipes versus a well-engineered performance exhaust.
Testing the Theory
65-MPH, No Muffler
70-MPH, No Muffler
65-MPH, With Muffler
70-MPH, With Muffler
The original dual exhaust looked good from the rear and made the Ram sound like a big rig.
Check out the difference with the Banks system. While some split-dual exhausts can deterio
While we could both feel and hear immediate improvements, it's revealing to review the actual before-and-after numbers. This performance and sound data, gathered by Banks engineer Dain Pankratz, tells the whole story:
*Backpressure as measured at the turbine outlet pipe was virtually eliminated. The biggest gains include a 1.37 psig drop in backpressure, to almost 1/4 psig (that's an 83.5 percent reduction)
*0-60 mph acceleration was improved by 0.4 seconds.
*Exhaust resonation and drone dropped 7 decibels at cruising speeds of 70 mph, for a 66.7 percent improvement! (A drop of 7 decibels is perceived to be twice as quiet).