You know you spend too much time on airplanes when you break down and buy a set of Bose noise-canceling headphones instead of that short-shift kit you've been pining for. But the technology works and the peaceful quiet, with none of that water-torture droning from the engines and hiss of near supersonic air rushing past, makes it all worthwhile.
For years automotive engineers have tried to come up with a way to use this same out-of-phase noise-canceling idea (it was first discussed in the '30s) in exhaust systems, with little success. There have been experiments with flaps, diverters and electric controls, but muffler technology hasn't changed much in a hundred years. Despite years of research, the automotive industry has carried on with either restrictive reflective mufflers that fold the exhaust path back and forth through a series of chambers or absorptive systems, usually a perforated pipe surrounded by sound-deadening material, that flow better but are less durable (some mufflers are built using a combination of both ideas). Sure, the materials used have improved (spun volcanic rock instead of fiberglass anyone?) and we've learned a great deal about quieting and managing the flow of hot combustion gases, but the basic ideas are the same ones we've been using all along to quiet the internal combustion engine.
Fifteen years (or so) ago, the innovative lads at Lotus Engineering developed a prototype system that used the vehicle's audio system, augmented with several microphones and additional amplifiers, to electronically quiet the cabin. It was effective but added expense and weight and did nothing for the noise generated outside the car. There have been many advances in active noise-cancellation applications since, most in industrial situations. Large fans and stationary power generators come to mind, but packaging requirements and expense have kept active noise cancellation technology out of automotive exhaust systems.
In 1997, the innovative engineers at Corsa Performance Exhaust used a C5 Corvette as a test mule for a new, passive noise-canceling exhaust system. After eight prototypes, they were able to patent a new Reflective Sound Cancellation technology that generates the same 180-degree, out-of-phase waves as active electronic systems. Essentially a straight-through pipe, a full radial air gap just inside the muffler allows sound pressure waves to escape into a dead-end channel. Reflected back 180 degrees out of phase, these waves cancel out that particular frequency.
Recently, UUC Motorwerks announced a new line of E36 and E46 BMW exhausts developed with Corsa's RSC technology. Until now, it was available only for select American muscle cars, trucks and SUVs, so this is Corsa's first system for a European car. With claims like, "The result of the UUC and CORSA partnership is a drone-free exhaust system, delivering a pleasant sound at idle and cruise and a muscular roar at high rpm"; "true bolt-on installation"; and "the all-new TSE3 is the absolute best performance exhaust system for '00-'04 330, 328, 325 and 323 models (i, Ci, iT-not for Xi)," it seemed worth a visit to UUC's Hillsborough, N.J., headquarters to check on the hype. Turns out the boys might be onto something.
Development of the systems began with Corsa engineers using acoustic and thermodynamic equations to generate a starting point and a "first guess system" that UUC then took to the dyno. The resulting system, now with differential pipe sizes to maximize torque and power gains, was then shipped back to Corsa where it was fitted on a car. Real Time Spectrum Analysis equipment was used to gather sound data from both inside the cabin and outside the car at idle, acceleration and cruise to determine the final sound tuning. After road-testing the prototype system, UUC gave Corsa the go-ahead to start fabricating the 100% 304L stainless-steel systems.
I was somewhat skeptical, having heard the phrase "bolt-on installation" one too many times in the past. UUC's Sunny Sabnani offered to install a RSC36 E36 M3 cat-back system during my visit. By the time I'd taken a few photos and changed into a work shirt, he was nearly done. Granted, he had bolted the two-piece set together before I arrived, but the fit was near perfect and the installation problem-free. On our return ride, the exhaust note was clean with no noticeable drone while cruising (65 mph) at part throttle, and though not objectionable it was noticeably louder. According to informal testing (same roads, speeds and operator) with a hand-held Radio Shack audiometer, the new exhaust averaged 1.5 dB louder than the older stock system it replaced. Throttle response was noticeably snappier and the engine seemed happier throughout the rev range.
E46 cars have their catalytic converters built into the exhaust manifold rather than halfway through the system like the E36 and so have the advantage of replacing nearly all the exhaust plumbing while staying emissions compliant. Early cars had a one-into-two system, while later cars had a true twin pipe exhaust. The added length means a four-piece system for these cars and the advantage of using six Corsa elements for even greater sound control. Driving a late model 330 showed no drone while cruising at 3000 to 3500 rpm (87-89 dB) at part throttle or while lugging around the parking lot, and the cabin was comfortably quiet the entire drive. Lifting from full throttle in third gave an odd little burble, and accelerating hard through 3500 rpm also briefly found a louder warble that quickly gave way to a quieter, joyous exhaust note all the way to 7000 rpm.
Back-to-back drives in two similar, high-mileage 2000 323s showed the UUC TSE3-equipped car to be even quieter than a well-maintained stock system. (Though both were wearing snow tires from the same manufacturer, the models were different.) No odd droning, chassis harmonics or vibrations were noticeable in either car. And as with the other versions I drove with the UUC/Corsa exhaust, the little six never sounded better at full throttle.
Reluctant to make extravagant power claims and knowing every car and dyno combination is unique, UUC's Rob Levinson nonetheless admitted their dyno testing had shown torque and horsepower gains of 5% to12% for the various systems. The earlier E46 cars benefited the most, going to a true twin pipe-style exhaust, while the 2004 330Ci test car showed an 8% gain in both maximum torque and horsepower. Even better for those of us looking for a more aggressive full-throttle sound, the systems come with a certificate showing full compliance with the SAE J1169 95 dB sound test now the standard in several states. UUC's RSC36 cat-back system is available for all 1992-1999 E36 cars with the exception of the 323 and 318. The TSE3 cat-back system is available for all 99-2005 E46 cars with the exception of the M3 and Xi models.