I just watched a video on a car with what looked like possibly dual 3" that was dynod first with no cats then with and it gained 3 hp with the cats , I'm sure different applications r .... Different , but I had that old cat removal thing pop in my head n saw that video and I think keepn them is better for me n people that breath air.....?

 

if they took off the restrictive 2 inch exhaust with high back pressure mufflers and put on a 3 inch system with free flowing cats and mufflers, yes that would increase HP.

 

Modern catalytic converters are very free-flowing and the idea of removing them for performance is outdated.

In fact, looking at basic exhaust flow theory (and real-world testing), a long and uninterrupted straight pipe can build up a standing wave resonance, a harmonic that actually creates backpressure and exhaust restriction.

By adding another element in the middle of a long pipe, either a resonator or catalytic converter, this type of standing wave get broken up and flow efficiency increases.

This is not just speculation or theory; as part of my job, I do exhaust design and testing.

 

Thanks for the input and knowledge ,