snippet: The factory (OEM) catalystic converter (Cat) is very restrictive on the exhaust flow in the exhaust system. Exhaust gas must pass through tiny "honeycomb" passages in the OEM cat which restrict flow and cause turbulence which in turn hinder performance. By removing the OEM cat with the Evolution Racewerks Test Pipe, power is unleashed! <br><br>The K03/K04 turbine (exhaust) outlet is almost 3" in diameter. That is why Evolution Racewerks' test pipe features a 3" design that reduces to 2.5" (to bolt up to OEM and most aftermarket downpipe/exhaust systems). Also, Evolution Racewerks use a "flare" type reducer to reduce the size to 2.5" instead of the "step" type reducer. The advantages of the "flare" reducer is that it has a nice smooth transition which causes less turbulence than the step type reducer, therefore producing more power. Also, having the transition as far as possible to the turbo improves performance as well.<br><br>The Evolution Racewerks Test Pipe's 3" to 2.5" design is superior over other test pipes that are 2.5" in diameter from inlet to outlet because the 2.5" test pipes will have a "step" right at the outlet. Since the OEM K03/K04 turbos have a turbine (exhaust) outlet of almost 3", the flange of the 2.5" test pipes will actually make a "step" right at the turbo outlet. This step acts like a wall against exhaust flow and when the exhaust hits it, major exhaust turbulence is created, at the worst spot possible, right at the outlet of the turbo. If you have a 2.5" test pipe, check it out. Look at the inlet flange and you will see a "ring" of carbon deposits on the flange. This is the "step" that the exhaust flow is hitting.<br><br>The Evolution Racewerks Test Pipe is completely constructed from quality 304 stainless steel and is polished to a mirror finish. The pipe, flanges, oxygen sensor bungs everything is 304 stainless steel, even the welding rod Evolution Racewerks use. The piping is fully mandrel bent. Evolution Racewerks test pipes are 100% TIG welded for quality and strength. The flanges are welded inside and outside to the pipe for added strength and extra longevity.<br><br>True to ER standards that Evolution Racewerks' current customers enjoy, everything needed for installation is included. That includes downpipe inlet gasket, Every bolt, nut and washer that is on the catalystic converter/test pipe is replaced with high quality full stainless steel bolts, nuts, and washers! Yes that's right Full stainless steel, down to even the hardware.<br> (Page 1)