I did search, a few times.
I herd the pre-cats are only needed for start up emissions.

Do they cause any issues when gutted?

crazy Backfiring, raise in exhaust sound, sound shitty?

I hear abunch of bad things about gutting the main cat, if this smog goes good I just wanna take off the main cat and run a straight pipe till I gotta do emissions again, so if I gut the pre-cats would it do the above?

Also anybody know of a cheap presilencer that'd replace the stock cat (bolt on fit) I'd rather run that then a "test pipe" since the corksport is too loud and with the silencer its too quiet and the car performs like crud when the silencer is in.

 

S5 don't have pre cats.

 

S5 FSM says they do have precats.

Yes, the precats are only there to reduce emissions right after startup. Once warm, the main cat does almost all of the work. If your main cat is in good shape, you can pass smog with it alone (I have). Gutting the precats will not cause backfires, removing all cats will do this, but really it's not a big deal.

Buy a corksport presilencer (they call it a race pipe). It's the exact same length as the stock main cat, and reduces sound by 5 dB @ 10 ft. (corksport rep gave me this info). It's $149. http://corksport.com/store/category/...rx-intake.html

 

Does the gutted pre-cat cause any nasty sound issues like the gutted main cat I hear?

I was gonna gut my main cat but I think its in pretty good condition the car passed smog with flying colors 2 yrs ago so I was thinking of just using the main cat whenever needed, otherwise I was gonna gut it and see how the nasty sound is, People told me its horrible sounding and to get get a damn mid pipe lol..

Hmm, i wonder if the pre silencer would work as good as the silencer in the muffler I don't know dB levels in my head, without the silencer in the muffler the car will shake my house's windows and kitchen counters O.o

 

You probably won't notice much of a change in sound if you only gut the precats. The main cat will still be there blocking sound waves.

Running just a straight pipe is very loud even with RB mufflers. I ran this setup for a long time, but ended up getting a corksport silencer to cut down on sound. 5dB might not sound like much, but it is much quieter than a straight pipe.

 

I'll be getting a magnaflow muffler to replace the cat and have the muffler shop weld the stock cat heatshield to it so it looks stock hehe.

Turbo II Rotor convinced me not to waste the tme to gut the precats, I'll be getting a header in a few months anyays.

 

remove all converters, replace with single high flow converter- you will still pass emissions testing and you will not have a crazy loud car.

Helps that you wont stink from exaust either like those who run no converter.
If you have no emissions testing definitly do your pre-silencer idea otherwise the car will get annoying to drive.