When it comes to the E46 M3 muffler, however, the vehicle design apparently did not lend itself to the more traditional twin muffler approach, necessitating a “split” within the single muffler case in order to feed the four tips. This design requires that the exhaust flow changes direction, as indicated in the following diagram, increasing back pressure. As there is clearly no room available to install a second muffler on the M3, improved flow had to come from design changes within a single muffler case.

Literally months of testing demonstrated conclusively that requiring exhaust gasses to make 180 and 360 degree turns within the stock muffler’s internal chamber results in a large increase in back-pressure. Our pressure-tap measurements indicated 1.1 PSI at peak power (333 hp @ 7900 rpm). Analyzing other after-market manufacturer’s mufflers revealed high backpressure readings as well, due to the fact that they employ a similar design to the stock system, albeit with larger internal chambers and tubing. This particular design also results in an exhaust note that is, apparently, unappealing to many M3 owners. The additional components necessary
to direct the exhaust gasses to the four tips also increases the weight of the systems.

Despite mounting pressure from M3 owners to deliver the Dinan exhaust, we made a conscious decision to continue working toward a design that accomplished our stated objectives. While we certainly would have preferred to begin shipping the systems sooner, I simply won’t accept compromises when it comes to performance. We worked and worked at designs that would maintain the dual exhaust outlets, but each iteration resulted in a heavy, tinny sounding exhaust note with far too much back-pressure to produce any substantial power gains.

The Dinan Soulution
After analyzing many designs, we came to the conclusion that a more radical approach was required in order to produce a truly high performance exhaust. Further pressure tests and dyno runs confirmed our suspicions about the best approach for the E46 M3 muffler. Adopting a completely new design approach resulted in a significant improvement in flow, reducing backpressure by 82% at only .2 PSI. The exhaust note became throaty and aggressive, without being so loud that it would disturb or annoy any self-respecting enthusiast. Weight was reduced from 58 to 43 lbs., relieving the load by a full 26%.

As you can see from the diagram below, our M3 exhaust utilizes the two outlets on the right side of the muffler only. Recognizing that the four tips have become a significant visual design element for modern M-cars, as well as the fact that the rear valance has a cut out for the tips on the left side, the second set of tips were retained. While they are non-functional, the Mcar look is retained without compromising performance. The 3" tips have been ceramic coated for a striking high performance look, while eliminating any concern over uneven discoloration
that would occur with polished stainless. Surveys conducted among M3 owners verified that the audible source of the exhaust output could not be pinpointed as coming from one side or the other. The Dinan Free Flow Exhaust was ready for production.

The system produces measurable power gains, looks great and produces the exhaust note M3 owners have been waiting for. I believe that this latest exhaust design underscores the importance of real engineering, extensive testing and employing the highest quality materials. BMW-like fit and finish combined with the best warranty in the business makes for the definitive solution for your high performance M3 exhaust.