SP Concepts Big Bore 2-Into-1 Exhaust System For Harley Dyna The Big Bore Exhaust shares a number of design features with the Lane Splitter and Cut Back Exhaust systems, but utilizes a larger 4 1/2 diameter muffler capable of keeping up with the biggest v-twin motors. Triple stepped headers and a stepped baffle round out this made in USA stainless steel system. Features: 4 1/2 rolled cone muffler offers increased flow for high performance applications Designed to work with properly tuned high performance motors from 88 to 143 Stepped 2 1/4 to 2 1/2 baffle for increased mid-range torque .065 stainless headers step from 1 3/4 to 1 7/8 to 2 at the collector TIG welded by hand from top to bottom Machined stainless header collars 18mm O2 bungs with 12mm adapters for performance and stock O2 sensors Includes all hardware and brackets Heat shields available separately Available in a variety of finishes: Stainless, Polished Stainless, Black and Black Onyx Works Edition pipes are precisely pie-cut and tig welded back together by hand Note: This pipe should not be installed without a fuel tuner. This pipe is designed specifically for high performance applications and is not recommended for stock motors.