My cats were hollowed due to them being plugged and at this moment, not enough for new ones so, like above, crushed out.
Question,
I hear everyone say these are loud as F&^% with hollowed cats, yet, my car is barely louder than it was with them before. Just a little tone now, over before.
Am I wrong? Car has OEM mufflers replaced little while ago and new y-pipe, obviouslu y has nothing to do with it. Do the oem mufflers work that good?
I will take a sound clip this am/pm, 3rd shifter, too late now.

 

As far as I know cats don't really have the same effect on sound as a resonator or an increased diameter in piping.

They just kinda scrub your exhaust gases.

I mean.. if you gutted your cats and it didn't really change the level, then what do you want to know?

 

Like-new Mazda mufflers will quiet it up somewhere around as much as Racing Beat ones.. So I've been told..

So all things being fairly normal you will still have a fairly quiet exhaust [stock manifold turns down the sound too]

 

I was just wondering as, I saw threads on here while searching, that stated if you hollow out the cats, the car would be crazy loud.
When I started it after it was done, I was waiting for the worst, just to be surprised that the sound level, wasn't really any louder than with both cats still in place.

Any affects I could experience without them "working"?
Some will say its gonna smell like crap, but honestly, even with windows down and sunroof open, I don't smell anything more than before.

 

yes they actually do, much more than most kids on this site give them credit for. most people should opt away from the stock catback for noticable gains only beyond about 350 wheel horsepower or if you are tired of the sound they give off and want something with a different exhaust note.

people who say that it is restrictive really just don't know and are making excuses to swap it out.

they are quieter than racing beat still but do not flow quite as well as the racing beat cat back does, which will start noticing drops in performance beyond about 400-450 wheel horsepower.

 

i put a gauge in the 6 port line on my stock s4, and it does about 4psi of backpressure = not bad, but not great. my car is 100% stock too.

going from 5psi to 4 psi, was noticeable on the butt dyno too, butt dyno and the pressure gauge actually agreed, which was weird.

 

i don't remember the size of the piping but i do believe there is both diameter differences as well as internal differences between the turbo and non turbo catbacks, i should have also mentioned i switch between a 3" single catback with borla XR1/fart cannon and the stock S5 turbo catback and didn't notice almost any difference at 15psi/T70 turbo.

when i put the Bonez main cat in place for e-testing it took a dirt nap and felt like it lost about 25% total power. the cat is virtually new also.

 

It does seem to pull a bit harder and top end seems a little better, though that could be "placebo effect" not that it was why they had to be hallowed out anyways. Still is a big piece of metal (not the ceramic material) broken off in the big cat, can't get it out. Eventually I will buy the whole exhaust, header, and full exhaust, just have to save for the good kits...

 

I can't throw fancy numbers at you but I can say when I have my hollowed cats on vs my non-hollowed cats I can honestly say there is a noticeable difference in butt dyno power... even my gf noticed the difference whether she was driving or sitting passenger.

Sound level however virtually stays the same.. maybe just a tad bit louder with hollowed cats but hardly at all.

 

That's odd... I felt a noticeable gain when I swapped from a RB header/presilencer and stock catback to the RB catback.. [Stock catback was ~143K but no appreciable rust on the outside, no rattling]

 

My car also didn't go loud when i gutted out my cat, and like stated by some here, you do notice a bit of a gain but not highly noticeable. Just be sure to not cheap out and buy a legit exhaust kit for it.

 

thats true actually, the s4 NA stuff is TEENY. the s4 NA gets a smaller y pipe, the muffler cans are smaller too, and the tips coming out of the muffler are like 1.5", if you buy new you get the big y pipe, not sure about the mufflers though, worked at a dealership for 10+ years and we sold a ton of y pipes, but nobody wanted to spend $600 each on a muffler....

you're right about the cat too, i put a cat in my old T2, and it went from being awesome to sucking so bad i sold it like 2 days later. power was close (3" cat) but response went from awesome to none...