For the few of us that are still concerned about blowing smog into the atmosphere, i have an idea. Although I very much doubt it will hekp you pass emissions testing, I think it will reduce a lot of hydrocarbons in the exhaust. Tell me if you think it will work, but i dont want this to turn into a 'death to emmisions laws' type thread.
You know how some guys re-pack glasspacks with stainless steel wool? Well I was thinking that you could re-pack it with half stainless steel, and the rest with chunks of catylitic coveter stuff from your old cat. You could just weld the old connection for the airtube from your old cat to the glasspack. The material would get hot enough to glow and turn some of the hydrocarbons into CO2 and water. And you would have a silenced highflow exhaust. What do you think?
By the way, where would you buy stainless steel wool? Ive never seen it sold anywhere.

 

If youre going to do that, just weld a high flow cat up to where the muffler usually goes. Little dangerous for my tastes though.

 

for one thing, the exhaust may not be hot enough at the end of the pipe, and also high flow cats are expensive. My idea is for those of us with little $ ( 90% of us )

 

The only problem with that idea is that the exhaust gas must come into contact with the catylist (the brick) in order to react. If you packed the catylist, like stainless steel, it would only very small portion of it's surface area exposed to the exhaust gases, and the exhaust gases would only be able to contact the catylist through the small holes of the preforated tube inside the presilencer/cat.

 

Thats it true. Yeah it probably wont do much for emmisions testing, but i think although not much gas comes in contact, just the fact that the air is being intoduced to the system with burn off a lot of hydrocarbons. Because at that point the exhaust gasses are hot enough to burn the oxygen being intoduced. I think this is the main way it will reduce emissions.

 

I'll have to check an old source from my UPS driver days, but I can probably still get 2.5" high flow cats that have to be welded in for $60. My source closer to my house that does my regular exhaust work sells his for $86 with a 1-yr warranty. I inspected both of these against the Random Tech cat I had originally installed and they all were identical down to the spacing and size of the cells in the honeycomb matrix. These are all 3-way cats, BTW...