Welding OEM Secondaries or Resonators?

[x Spades x]

Hey Guys,

I've been reading a bunch of threads and I see people buying xpipes, then buying aftermarket HFCs and resonators (vibrant fir example), to elevate rasp and/or drone. Why don't people weld in the OEM secondary and/or resonators? Dint these flow extremely well? Buy the size of them, i figured they would cut out any and ever non wanted sounds. The resonators are HUGE... and I figured the Sunday cats can be welded in the primary location, to pass emissions.

Am I missing something?

Kareem