spec i've used for checking cats is 2psi @5000 rpm in park or neutral. but i've never actually tested one that was that low, because i'm only checking them because of a customer complaint where i think the problem is the cat and it is only tested to confirm the problem before dropping the big bucks ona new cat.... well my point is, could have someone test it, and see if there is excessive back pressure.

i've also heard of people getting much better mileage when thier converter is getting plugged up... not sure why that would happen, but i've heard of it.

and my last 2 cents... i think in iowa fines are $10000/shop, $1000/person for removal.

it looks like that regardless of if you save gas by removing it, it still will not offset the fine if you get caught with it off of your vehicle.

yea but for us in non inspection/annuall check of any kind, whos gonna check?

tire store didnt say a thing about missing the cat off my car (quite obvious as a straight pipe is welded/clamped in place)

and any cop that pulls me over isnt going to get down on his hands and knees to look...

I am not located in an emissions check area but people report that police may visually check for a catalytic during a safety check. You probably wouldn't get caught if your straight pipe was shaped like a real catalytic.

My 91 Camaro had a disintigrating cat. Whack it and you could hear the pieces rattling. When I took it off I could pour out the tiny bits, and see the bigger pieces moving around. I took a long, pointy piece of rebar and broke out the entire insides.

It sounded different, but since I wasn't all into FE at the time I didn't see if there was any change in mpgs. It did sound a little better, though.

Nobody would be any the wiser of it unless they took off the cat and looked through it. Who's to know?

But with people here throwing parties with an FE gain of .5 mpg, it may be worth a try.

You could also hollow the cat and shove a straight pipe through it.

I'm a member of a forum full of people who have removed their cats, and have never heard of anyone getting in trouble for it. I suspect that enforcement is nearly non-existent except for emissions inpsections.

I remember on my 1980 Pontiac wagon the cat was partially rusted and leaking. Being 17 at the time and not having the $400 needed to replace the cat at the time I took it to a welding shop and had the cat welded back shut for like $5.

-Jay

That's the best way to do it. Just hollowing out the cat means you end up with this dead space in the exhaust where the gases expand into the cat chamber and then get recompressed into the exhaust system again. Usually this is no big deal because the honeycomb in the cat keeps the air flowing in one direction and without much turbulence but without the air direction it becomes a mess in there.

I had a 94 Astro where the honeycomb in the cat shifted and clogged the exhaust. Disconnected the tail pipe, broke it apart, and revved the engine to blow the pieces out the back. Noticed no performance loss or change in MPG.

One of my horsepower books mentions the theory and construction of expansion chambers for horsepower. The cats are placed in an agreeable postion for such a job. I can't remember the details, but an empty cat not modified by a straight-through pipe might be useful.