Restrictions in the exhaust system rob horsepower and torque, especially on turbocharged cars.  Thus, removing as many exhaust flow restrictions will increase horsepower and torque significantly.  The factory catalytic converter found in the factory downpipe is a big culprit of this and is a major exhaust flow restriction. The factory catalytic converter is made up of catalyst material formed into "honeycomb" weaves. Exhaust gas must pass through these tiny "honeycomb" weaves on its way to the exhaust system thus causing a major exhaust flow restriction. It also causes turbulence after the catalytic converter which causes the exhaust flow to slow down (which increases restriction). By replacing the factory downpipe/catalytic converter with our Sports Series 4" High Flow Metallic Catted Downpipe, more power is unleashed! 

The factory catalytic uses a 900 cell ceramic core. What the 900 cells mean is that per every inch, there are 900 "cells" that the exhaust gas must pass through. We use a 200 cell metallic core. By having fewer cells per square inch, these individual "cells" are bigger in size thus allowing exhaust gas to pass through it more easily. Thus, the lower the cell count, the higher the flow. Higher flow = more power, faster turbo spool up (less turbocharger lag) and better throttle response. Bottom line, faster. The benefits of a metallic catalytic converter vs a ceramic-like factory unit are that it can take higher temperatures and is more durable (last longer). They are also lighter than their ceramic counterparts.

Our Sports Series 4" High Flow Catted Downpipes is constructed out of 100% 304-grade stainless steel and utilizes mandrel bent piping.  They are 100% TIG welded by our in-house fabricators and built in the USA.  The factory turbocharger turbine housing utilizes a 4" V-Band flange which we have duplicated and CNC machined cut out of billet 304 stainless steel.  Stainless Steel CNC machined O2 sensor and laser cut brackets are TIG welded using stainless steel rods.  The O2 sensor is positioned at the factory location.  Since the outlet of the turbocharger is 4" and the factory exhaust system is 3", the factory downpipes reduce size using short transitions from 4" before the catalytic convert and 3" afterward.  Due to the space needed for the catalytic converter, the factory downpipes reduce in size using very short transitions.  We use very long transitions.  These longer transitions allow the exhaust gas time to smoothly transition from the larger piping to the smaller.  This results in less exhaust turbulence and backpressure which again improves throttle response and increases turbocharger spool times (less turbocharger lag). 

The factory downpipe utilizes a flex bellow section that allows the exhaust system to move.  This eliminates undue stress on the exhaust components like the exhaust system, downpipe, turbocharger, and exhaust manifold.  Many of our competitors do not feel it is important to keep this.  While you do not see any adverse effects right away, over time, the stresses caused by not having a flex section and having a rigid exhaust system will cause premature wear and tear.  Any stress failures like cracks will form quicker than usual on exhaust manifolds and exhaust components.  Also, without a flex section, the exhaust system cannot properly deflect impact.  Especially on lowered cars, whenever the exhaust system contacts the ground, the entire system gets pushed up.  Without a flex, you can imagine how much stress is put into exhaust components like the exhaust manifold when the exhaust is pushed upwards.  We fully understand that durability of our products is important.  Thus, like BMW, we incorporate a flex section into our downpipe.  Our flex sections are 100% stainless steel (cheap flex sections only have stainless steel center braids and steel caps) to ensure corrosion resistance.  

One of the main features of our B46/B48 downpipe is the CNC machined solid stainless steel billet ball joint.  The factory downpipe uses a press-formed process to produce the "ball" joint to connect to the factory exhaust.  This process can be done very inexpensively when done in large production runs.  Unfortunately, the drawback of this press-formed "ball" joint is that the interior of the pipe also mimics the outside.  When exhaust flows through a pipe, the majority of the exhaust flow tends to stay on the outer edges of the pipe.  Thus, when exhaust flows into the "ball" section, it goes into the valley created by the "ball" joint and then back up the other side.  This creates tremendous amounts of turbulence in the exhaust flow right at that section.  Turbulence, in turn, slows down exhaust flow velocities as well as increases back-pressure.  It's a well-known fact that with turbocharged cars, you want the least amount of back-pressure while still maintaining high exhaust flow velocities.  Why?  Because low back-pressure and high velocities allow the turbocharger to spin faster.  This equates to reducing turbocharger lag and faster spool times.  Throttle response is also improved.  We had originally thought to use the same press form process to manufacture our downpipes.  However, very quickly we noticed this flaw to the process and decided to CNC a solid stainless steel billet "ball" joint.  This allowed us to keep the factory connection while keeping the interior of the ball smooth.  This allows the exhaust to flow unrestricted through the "ball" joint.  While this CNC solid stainless steel billet was very expensive to manufacture, our motto at ER is "Performance, no compromises".  Our in-house testing showed that we did indeed have real-world improvements with this new CNC billet "ball" joint and thus worth the extra costs.  This is why the N26 downpipes do cost a little bit more than the N20 downpipes as the N20 downpipes do not have the ball joint system but use a traditional slip-fit design which is cheaper for us to manufacture.  The pictures below show the factory "ball" joint cut in half (to show in the interior) versus our CNC solid stainless steel billet "ball" joint. 

Since we are able to reproduce the factory "ball" joint v-band connector, our downpipes are designed to fit perfectly with either the factory exhaust system or your aftermarket exhaust system.  There are no compatibility issues whatsoever.  The downpipes will come by default with a brushed finish.