just cut about 6 inches off the factory exhaust and welded a 6x3 piece of stainless steel in its place . the bike sounds amazing and feels like the it has way more power. Suzuki installed some type of filter for emissions purposes that restricts the back pressure of the headers and quiets down the exhaust sound . after removing this piece and welding in a new straight pipe the bike is a lot louder and feels more crisp like a full aftermarket exhaust. I recommend this mod to everyone. feels like a new bike.
I’m thinking about doing this too, currently I have just a M4 slip on which sounds great but I want to be louder. What did you do with the butterfly valve and the o2 sensor before the cat? Also did you get a tune or is the bike running fine without one.