From every muffler shop to 2 different tuners including the one I use here in Reno there is no such thing as a "HI FLOW CAT" they all suck for flow I would think some flow more the others but its still a dam restriction either way no 2 buts about it. If you have smog where you live a cool solution might be what I did on my 89 5.0 when I lived in the CA bay area. I would just pull my x pipe off and put the factory cats back on then retard the timing to stock and she passed every time. If you have 4x4 on your truck it would be a little bit of a job to do but should only take you 2 ½ hrs tops once you’ve done it a few times. The only hard part would be finding a junk yard with the stock cat set up willing to sell it to you at least in ca at the time the stupid junk yards wouldn’t sell me the stock set up so I came to NV to buy mine back in the day. of course if you went the long tube route this would throw a whole new monkey wrench in.

 

Why is everyone against running the factory cats straight piped ?
I have 2 1/2 " duals from the Tcase back with 4" tips coming out behind the tires and it's not loud at all. Hell my 71 year old Dad had both his LT's done the same way. Not obnoxious but a deep rumble. Shorty headers no cats, 2 1/2 from the collector to 3" to the Y then 3 1/2" with a magna flow is certaintly louder.

 

ohh......ok............that explains alot then
x49!!!

 

I’m not against it at all and that is what I originally did my self. I just felt the factory Y was a major choke point and that my old Flowmaster cat back set up was stealing power in which I turned out to be right in my case. I still have the gutted pre cats and about 8in on both sides of the collectors stock set up until I can decide if I need full lengths or not. I also thought about taking your route at one point and even wasted $50 on a 2.5 x pipe I never ended up using. I started asking a lot of local performance guys around Reno about there thoughts of 1 big single set up vs. a 2,5in dual set up and all most all said its better to have one big system then 2 small duals. All I can remember hearing from most was a 3.5 would out flow x2 2.5 true duals which = 5in total why I don’t know but I did what they suggested and like it so far.