VRSF 3.5″ Ceramic Coated Downpipe N55 10-13 BMW 135i/335i/X1MFG# N55EX100 The VRSF 3. 5 downpipe upgrade is THE best bang for the buck mod available for your N55 135i & 335i xi. By eliminating the restrictive catalytic converter in the factory downpipe, back pressure is significantly reduced which results in faster spool, an increase in power & a more aggressive exhaust note. Our downpipe also features a unique CFD optimized cast merge collector which offers the smoothest turbo to mid pipe transition