[BI had this write up in the exhaust/headers forum when i went with new cats. Read below.

Ok, I wanted to update this thread. I did order new cats but before installing them I ran my truck for one month with straight pipe. Below is my write up.

Install:
This was very easy. I just bought a bunch of angled pieces from the auto parts place and then returned the ones I didn't need. The pipe size where the cats is is actually 2". I read a lot of differing sizes but they are 2"...they were on mine anyway.

Sound:
Way more aggressive sound. I liked it...a lot. But if your not into a raw V8 sound then you would not dig this. Also I think it would have probably sounded better and maybe a bit quieter if I had welded the pipe. I just used clamps so I had a few little leaks.
It was not too bad in the truck. On the HWY at 65 it was pleasant, nothing obnoxious.

Power:
I did not notice anything. But to be honest, would you really notice anything under 10HP unless you put it on a dyno tester.

MPG:
Mine went down. After the straight pipe install I lost roughly 30miles on a tank. It was hard to tell because the pipes were not welded so maybe the leaks caused a bit of fuel drop. also it got a lot colder out right after I did this and my truck get worse milage in the cold and also the O2 sensors were constantly throwing me codes so I'm not sure if they sent signal to pump more fuel into the engine or not. So MPG was kind of inconclusive but It definetly did not get any better milage. I'm just not sure it if was worse.

Smell:
Didn't notice anything inside the truck or out.

Codes:
I did install the spark plug non fouler spacers but I'm not sure of they really worked. My rear driverside sensor threw a "not working" code P0137. Then I dropped one of the spacers and that went away.
My passenger side ddi the same thing. P0157. I'm not sure if this was due to a bad O2 after screwing it out and back in or if it was not working from the straight pipe.
Seemed that every time the CEL went on I had a new code.

In conclusion:
Well I would for sure swap your cats out. New high flow cats are cheap and Mine were under $100 for both. I sold my factory cats on ebay for just over $250.00 for both. to be honest though if you are thinking about doing straight pipe for any type of gain in HP, milage etc...don't bother. It's not worth it.
Also another thing that I noticed was my engine knocking on start up every morning. It never did that before.

 

I just looked it up. WOW
That has to be a misprint!

 

Not to my knowledge, no. Is your check engine light flashing or just a solid illumination? Flashing means misfire, no flashing means no misfire.

Here is the Amazon link again: http://www.amazon.com/dp/B005M1AVFQ/ref=cm_sw_r_an_am_ap_am_us?ie=UTF8

And the Android app link: https://play.google.com/store/apps/details?id=org.prowl.torque

 

so other than environmental considerations what function(s) do my catalytic converters actually do?
and once they are removed I can expect to get constant O2 senors error codes?
Thanks

 

If the post cat sensor is reading unchanged exhaust from the forward sensor an error code will generate for faulty cats as the emissions did not change. The computer can sometimes perceive a lean condition and compensate by increasing fuel to the engine. This will cause a noticeable drop in fuel mileage. That is why some use the spacers. Pulling the rear sensor slightly out of stream will reduce the reading and fool the computer. If you pull sensor too far out it will throw an error code for a bad sensor. A rich fuel condition, created by the computer improperly compensating, can send raw fuel into the exhaust and combust in the exhaust and do damage to the cats(if you still have them) and generate misfire conditions.

 

I wish someone would come up with a reliable solution with no check engine light for our trucks, because I'd like to just chop mine out and be done with it too. Not so much for power or gas mileage, but for sound. And maybe for a little extra power, though probably barely noticable over the high flow cats. That would leave me with true straight through exaust becasue the Borla has a straight through perforated core. No matter, when I get my headers I'm also going to get pre-cat exhaust cut outs for when I want to be loud and flow-ey. Another plus would be that going cat-less would solve our driveshaft issues.

Oh, and to correct a previous post, the Y-pipe is not 2" diameter, it's 2 1/8". Wierd size, nobody makes anything 2 1/8", I ended up getting one 2 1/4" cat and one 2 1/2" cat because it was what was in stock.

Oh, and something else. The same post said their engine started knocking on start-up without the cats. I've got a pre-cat exhaust leak that sounds a LOT like a knock from inside the truck, and a little so from the outside. The original poster may have been mistaken.

 

Of course, the way to solve the lean condition perception is to un-plug the rear O2s. It's not like they would be doing anything anyway. Perhaps a more complicated spacer setup with a piece of pipe with converter core could work, but sounds like a lot of trouble. Never know, I might get a hankering one day and give it a stab. I do have that extra OEM y-pipe I could always cut the cats out of.