Hooker Max Flow mufflers work great and are way quieter than you'd think. I have a pair of them in 4" on my cuda. They are actually quieter than I'd like them to be.

https://www.youtube.com/watch?v=28K935z94dI

https://www.youtube.com/watch?v=wBphOshIgiQ

https://www.youtube.com/watch?v=D3dQZJPMR68