[tirwin]

I found the same thing when I first bought my car -- cat had been hollowed out. I have zero scientific data to prove this but I personally believe the car runs worse with a hollowed out cat.

My personal opinion is use something that was designed for the job -- either use an actual cat, a test pipe or a premuffler. I suspect there is something about the turbulence of the exhaust gases expanding into the big chamber of a hollowed out cat and then being reduced again on their way to the muffler that is no bueno.

I bought a used test pipe and it was an improvement to me. I've always wondered if anyone has every taken the time to study this... but why would you?

Long story short, I'm currently running a Magnaflow cat with O2 bung and a 1-in/2-out exhaust. I'm getting headers and 2-in/2-out from Brian at M&K. The cat and the old test pipe will be for sale soon. The cat is a 49-state and has about 1000 miles on it. PM me if interested.