The "issue" is shutting the engine off hot, and some of the exhaust valves will be off their seat. Cold air going back up short open exhaust can unevenly cool the valve and warp it.

With a couple of feet of exhaust pipe, you don't have to worry about this. With a cat installed, no way cold air is going to get back to the exhaust ports.

The biggest issue with your "set-up" is carbon monoxide. What you're running is completely illegal in all 50 of the United States, and for good reason.

 

If police arent **** about sound, theyll be **** about polution, which imo they should be. A green earth is a good earth ^_^

 

Unless I read the OPs post incorrectly, he did a muffler delete, not a cat delete. I don't have any mufflers on my 78 Camaro and it passes emissions just as easily as it did with mufflers. Same goes for the 87 IROC I had for 4 years (and had to test it for 3 of those years and I know it's still passing emissions 2 years after I sold it).

 

Im just saying in general, if the exhaust system is not functioning correctly and something is wrong, for what ever reason, whether it be his cat, muffler, or what not. Pollution is bad ! .

 

If mufflers (or lack thereof) caused additional pollution then there's no way I would be passing emissions every year. Not only passing, but coming in at well under 1/4 of the allowed values. In fact, my 78 puts out less emissions than my 93 truck (that does have mufflers). Same size motor as well. That's the point I'm making. As long as the cat is on there and functioning, he's perfectly legal from an emissions/pollution standpoint as far as exhaust is concerned. The only issue would be dependent on how much noise it puts out, but that deals wih local ordinances, not emissions laws.

 

So he could basically run straight pipes, as long as he has his cat, and pass emissions? Even with or without the res? right?

 

Now that makes sense! I am running like 8' long pipes out, barely past my rear wheels. I only have one cat, that's in my downpipe, other than that it's just straight pipes.

Well, I've passed police before with it pretty damn loud, bubbling, and popping and they didn't seem to care. Although I am careful, lol got enough tickets and warnings already.

 

Sorry for the late reply in this thread. I live in the suburbs of Illinois and work for the city of Chicago so needless to say, I'm always running into cops and they have never said or even looked at my car funny. I was concerned when I first put the new Highflow where the res was because it was hella loud but after breaking it in after maybe about 1000 miles, it's gotten a little quieter. So with this set-up, I'm not concerned with the sound. Here's a video btw:

https://docs.google.com/file/d/0Bz9h...?usp=drive_web
Sorry for all the wind...

And no, I didn't remove the cat for that purpose. The muffler guy wouldn't even let me. He freaked out when he thought I wanted to. I don't want to have ANY issues with emissions.

My biggest concern and the reason for starting this thread is to find out really if there is a drop in back pressure because of muffler delete which it seems like you all have already answered. So I've ordered some 2 chambered mufflers which should be here soon. Hopefully it still sounds badass.

 

That is correct. I've been doing that for years and easily pass.

 

I know this is a bit of an old thread but I wanted to chime in anyway.

To my knowledge most the back pressure in the front wheel drive montes come from the u-bend in the exhaust.
My exhaust was done on my monte before i bought it previous owner decided to add a straight through glasspack and dual 3 inch 3 foot tips in place of mufflers. Feels like any other 3800 I've drove, gets same mileage.
I've heard some say that if your exhaust is to big at the end even if its open it can create more back pressure, example 2.5 pipe can create less back pressure than one twice it's size. Same drive train. I'm not 100% on this theory could very well be true though.

With carbed engines you had to re adjust carbs after exhaust work due to the change in vacuum, now days the computer does the best it can.

My buddy had a throttle body saturn, muffler fell off and he decided to add a really nice magnaflow can to it. After that his car was amazingly fast for what it was. My fuel injected version could not keep up until the end of 4th gear (100+mph). Point of the story is my buddy added extra back pressure and his low end power increased greatly high end power didn't seem to suffer, mpg's were still good to. To this day that engine runs perfectly but he's managed to shred a tranny and crack 2 sub- frames and for now it sits.

If your adding power you may want to open the exhaust, or maybe if your type of vehicle is known to have a bad design than you may want to replace with something different. If not then your just seeking the sound.