Dont know if it helps but I cored my stock 899 exhaust.I removed the 2 catalytic convertors. Did not hear much of a difference and thought I wasted my time UNTIL I took out my earplugs-it makes a difference! Much louder than stock and really brought a smile to my face.Personally I can recommend coring. I was shocked at how heavy the stock exhaust is.You can also remove the exhaust flapper,exhaust cable and exhaust motor ect. while your at it.I expect you will need a servo buddy to prevent alarm on dash.In my case the ecu flash included deleting the exhaust motor.