Dinan's Free Flow Exhaust for 550i models provides improved flow over the stock system without the excessive noise and ''boominess'' associated with typical after-market mufflers. The system is manufactured using 100% 20 gauge-304 stainless steel for optimum resistance to corrosion. In addition, the muffler is lighter than the stock unit. Internally, the systems feature Dinan's Tuned Resonance Chamber Technology, providing the optimum balance between maximum power gains and a civilized, yet sporty exhaust note. Dual 3-inch diameter polished stainless tips give the cars a tasteful performance look as well.