By not using the cat you might be hurting the environment but not by a noticable amount. If every vehicle on the road had no cat then there would be a problem. However the actuall # of vehicles running with no cats is a drop in the ocean. The 02 sensor is in front of the cat so the truck won't run any worse without a cat. It will probably run a little better. I'm not encouraging you to do it but it would run better. Ever seen a race car or truck with a cat on it? I'm sure the tree huggers are gonna rail me on this post.

im just saying, if you say if everyone had that mentality then a lot more people would be running w/o cats and it adds up. if you look at the emissions levels of a vehicle w/ and w/o a properly working cat it is drastic.

That's why ski-doo/quad manufactures will be trying to incorporate cats from 2008 or something & on. Actually, try treeplanting for a season, you will know what's a real tree hugger! <img src="/forums/images/graemlins/cheers.gif" alt="" />

At my shop we bend pipe for exhaust systems. Bigger pipe is not necessarily better. The right sized pipe will draw the exhaust out of an engine, too big a pipe will allow it to slow down and cause back pressure. I run a Hedman header with 2" pipe back to a NAPA Quietflow muffler with a tail pipe. I did weld in a cat, even though we don't have emissions testing here yet. One county away, but not here. Of course, the cat is only $30 my cost. But here is one thing to consider: Having the cat mounted close to the collector keeps your O2 sensor hot during extended idle and off idle running, which means you stay in closed loop.

Ok, you had to know you were setting your self up to get some heat over this. I hope everyone doesn't get this attitude. If so then the entire US will be one big smog fest.
I live in Oklahoma were there is no state inspections. and since this was incorperated in 2001 the number of people running around with out cats has increased dramatically. Not only hurting the enviornment but also horrible noise pollution with all of these little rice burners with chrome fart pipes. I too used to believe that no cat was better. But have grown to realize, uless you are trying to shave off a couple tenths off your quarter mile time, keep your cat on. They make high flow units that will replace your stocker if you want too. Here is a pic of a good flowing system using a cat. I since have cut the pipe off about 8" past the muffler cause I didn't like the pipe out the back. It has a header with 2 1/4" pipe and a Dynomax super Turbo. It performs great and sounds great.

I did my own test on my DD Rodeo, 2.6l.
W/out cat my mileage per tankfull increased about 25 miles, while the top wot speed increased 10 miles.
I think what the cat is doing is burning the small amount of hc left (don't really know how much) in the discharge.
Also used to remove egr circuits on bikes (F-3 and F-4 mainly) which added about 18-20% increase.
So I use a hollow cat, with a tube trough it, here in Cali is expensive to be cough tampering with emission related components.
I had run leaded gas on my Swift GTI, which had no impact on either performance or economy...
Just my .2 cents