I have an idea, but im not sure if it would work
Heres what im thinking, Take a cat, hollow it out, then take a pipe that will fit exactly inside the cat, drill 30-50 holes in the Pipe and then mount it into the Cat. That way you have a hollowed out cat, but still maintain some back pressure.
Would that work or am i just gone crazy
seen it done 8) …u have to chip away the walls of the cat which is like cement…drill a nice amount of holes weld it up and bingo :D…
It still effectively would be a hallow, punched cat man.
If you want flow but still have some back pressure you’d be better off buying a cheap high flow cat. Hell it can be a ractive one from Performance Improvements, cost you about a bill and no one needs to know your using it! 
That’s the best way to go man really.
Take care.
Easy 8)
spend the money and get a high flow cat… the last thing you want is peices of demolished cat material flying through your nice muffler or better yet plugging the shit up so you have 100% backpressure.
GT
or if you just want to pass visual, run a straight pipe and wrap a cat body around it.
i thought about that mike, but wouldnt that cut down on the back pressure? Dosnt the car need it.
There’s still back pressure, you have a pipe, don’t you? We need someone that knows the ideal flow requirements for the specific engine/turbo combination that you’re interested in and then you’d be able to get a rough number. This is not me… lol… I can give you some rough numbers for pressure and velocity in a specific exhaust, if I got to take some measurements and knew the massflow of exhaust for your setup.
I think they’re just isn’t enough cooperation, we have some extremely knowledgeable and talented people here and we could pool our knowledge to make some of the best SR/KA/RB, etc… 240s around.
just spend the 130 bucks and get teh all stainless flanged 3inch high flow cat from pdm
the idea is good
but there’s a catch, if you put a pipe inside a hallow cat… basically you’ll get like a pocket of air in the middle between the cat and the pipe that’ll basically be an oven since the air wouldn’t move, it just sits and the temp will rise. the inner pipe will get very very hot. and wires or stuff around it will get very very hot / melt
Heres what im thinking, Take a cat, hollow it out, then take a pipe that will fit exactly inside the cat, drill 30-50 holes in the Pipe and then mount it into the Cat. That way you have a hollowed out cat, but still maintain some back pressure.
you might loose some horse power because the hallowed cat will basically abrupt the air flow of the exhaust.
my friend who works at oxford auto sound which is beside PI on kennedy, scarborough did both suggested above, which the first one, it gets tooo hot. that if you drive to a show and parked your car on grass… it’ll burn instantly
and the latter one, he lost hp becayuse the exhaust will flow from a pipe to a bigger volumed cat. when the air reaches there, it’ll cause turbulence because the exhaust will go multiple direction when it reached the expansion of the hallow cat. and then scramble and squeeze into the smaller pipe. that mess up the air flow , no air flow in exhaust = no hp
my 2 cents 
Ed is right.
the best thing to do is take a cat heatsheild and put it around a testo pipezor and then put a peice of thick steel on the inside of the heat sheild so if a cop taps it it sounds and feels like its hitting a pipe.