When Pinks ran at my local track,they made a big deal out of not allowing straight through mufflers.At that time I had a 3.5 system,no H or X but they were long and round Ultra flows ending at the rear axel.So to run at pinks I had Jimi Vignogna fab a 4 inch stainless with an "X" going into 3.5 Hooker Aero chambers because they were advertised as a 3 chamber.When I pulled a muffler OOTB,,,,,,,,,,,