The AFE is 4.124" in diameter, according to my calculations this makes it a 84.5 of the OEM diameter or a 15.5% reduction if my calculations are correct.
2013 M3 Coupe-MR/BLK ZCP, ACM test pipes, BPM Stg2 dev. tune and Megan catback, more to come
Previous rides: 2011 M3 Coupe-MR/Blk
2007 Porsche 997C2S Speed Yellow/Blk sport seats
2004 BMW M3 Imola/Blk