yesterday i had a muffler shop weld on a slp y pipe w/the stock cats onto my borla catback. after driving it around i noticed there was a odd rattling/raspy sound/vibrating coming from under the front seats and pedals. after more driving the sound died down but is still pops up under 50-100% throttle. oddly though i've noticed the car has def. gotten quieter, it no longer growls under throttle and sounds stock when cruising even @wot it's def. quieter-is this normal? my understanding was the aftermarket ypipe would make the car louder and raspier not quieter

 

first is there any leaks?? the noise you describe under the seats may be a leak from 'bad' welds.

Anyway, is the car quiter when inside and outside or just inside. I say this becasue the y is more free flowing the sound will not resonate in the y pipe and flow out, vs. what the restrictive stock pipe is like. From experience we made a custon 2.5 true dual system for my pals gto, and it only has 2 very small mufflers (like dynomax bullets). inside you can hardly hear it but outside its as loud as hell at the rear when hes at WOT.

also if you can, get the cats off

 

the car does def. smell worse, same smell as when they were welding the pipes together, its quieter on the inside/outside/idle/wot. and it kinda sounds like metal rubbing against metal, it happens more often when its cold outside. my orig. plan was to hollow the cats but i'm finding a hard time finding a shop around here that will do it. plus it's my daily driver so i'm scared about getting a nice big ticket :/ preferably i wanna make it as loud as possible w/o headers(out of budget) while being able to pass inspection

 

usually the exhuast do take time to bed in and blow all the crap out so see how it goes, but if its leaking undernieth then it needs welding up right. its not a major problem but if you paid for it to be welded then it should be. The noise maybe the pipe scraping on the under side of car you'd ahve to look.

If you want to get it louder just replace the muffler with some pipe also, ie so your just running the cats and a pipe back. essentially thats what i have but 2 see cherry bomb style rear cans with tips

 

last time i checked the new pipes aren't touching the car anywhere so i think i'm good there, i guess i'll just give it a week or so and see what happens with the sound/smell. if it's still the same i'll take it back. i guess what i'll try first is take off the adjustable plate the previous owner put in which comes wit the borla catback. if that doesn't do it then i'll prob just take out the muffler. although i haven't been able to find any sound clips of that sort of set up so i'll have to look into it.
thanks!

 

Go for high-flow cats then.

 

Experiment with the plates, I believe Borla provides 3 different ones...

 

i've considered hf cats but i can't find them anywhere for cheap and i don't kno which ones would/wouldn't work or fit properly, any suggestions?

 

For high flow im sure something like this would be ok, they would have to go somewhere near the original location to fit or somewhere in the y-section:

http://cgi.ebay.com/ebaymotors/UNIVE...Q5fAccessories

I was laughing as i didnt realise HOW RESTRICTIVE your cats are, OEM are 500-990 cpi. In the UK OEM are 400-600 me thinks. But i can get a race cat with 100 cpi Make me hapy thats ill get a good few hp when i take mine out

Ill try get hold of a clip where my car sounds good, i have one on youtube but the camera is really crappy so doesnt do it justice ill get a better one when im back in UK, i miss hearing my car:

http://www.youtube.com/watch?v=FfQOahF3OoA

 

sorry for the noob question but since those hf cats in the link have a 3in inlet/outlet won't welding them on to the same place where the stock cats are be a problem since the pipes connected to the cats are much smaller?