can i put just a RT cat on my car without any other exaust modification? If so, what kind of hp increase and sound change could i expect? I've only seen the hp increase with more exaust mods

 

yes you can but the actual gains from just a rt cat are minimal

 

Yes you can install just that but why? unless your Cat is old and in need of replacement. I'd guess there would be minimal hp gains of 1-3 without a Y pipe.

 

what about hp gains with a downpipe? 5-10?

 

yes you can do this, but it wont really make a significant gain. i would suggest saveing another 100$ and getting a y-pipe. sounds good and will give you 10-15hp increases

 

i was also looking for a new cat a while ago, but then i read everybody's opinion on them, and realized its a waste of money. i got my y pipe and ive never been so happy with a mod! or you could get a testpipe, but those are bad for the earth( ), and also dont really give noticable gains either, unless youre SC'ed.

 

save up a little and buy at the same time...

Warpspeed Aluminzed Ypipe and their High Flo Cat...

Good prices on both and it will be a very easy install.