MJHSC400

I had a really bad exh leak right behind each cat at the flange due to broken motor mounts flexing the flanges and finally warping them badly--

Well, after disconnecting these flanges and having a look, big chunks of the cats were spit out and lodged in the cat exit-- seriously blocking flow--

I was glad to find this problem and went on to gut the cat the best I could and the other side looked the same except there were no obvious chunks to be seen...... What a mess--- got crap in my eyes -- man it sucked--

I finally got the flanges to seal up using the old gaskets AND some new 2.25" gaskets (crush style with the paper/copper material combo-- kinda spongy) --

So far the leak hasn't come back after doing this and replacing the motor mounts---

BUT, there is this nasty hissing/rattling from all the trash spit out by the cats in the center resonator, and maybe in the two rear resonators--

What is the best way to replace these resonators??

Will it be much louder if I just replace these with straight thru tubing and maybe a new custom fabbed resonator chamber about the same size as the original?

I would build the center chamber from 16ga mild steel and make it dual inlet dual outlet with no packing -- just a completely hollow chamber--

I would try to fab the exit/inlets with pipes on an angle to minimize the need for bends when connecting into the existing SS factory tubing--

I'm just thinkiing these factory muff's are as good as anything aftermarket and should have a nice mellow note--

JspecSC3

iTrader: (4)

Well now that you have your cats gutted you might as well have the resonators deleted. Your car will sound like a monsterous V8 killer. A friend of mine did that on his old SC4. Got performance gains from it also.

MJHSC400

There seems to be two cores in each cat-- I only gutted one of the two cores-- so there is still some function, if that function is only killing hp so be it-- I do have a much newer set of cats to go in-- but it doesn't look that easy to change them, and I may just wait and install some Tex's headers instead of messing with the old cats-- I'll just install my new one's with the tex's -- and maybe install a bung on them for the o2's while I'm at it-- Keep it all functional --

I still want to see some input on the center section being dual in dual out -- plus what gauge-- I don't have access to a break that can bend anything over 16ga, as I'd really prefer to use 14ga -- I guess that's pretty thick though-- 16ga may be plenty thick--

mwwfla

My cats are fried as well, because the car was one notch off timing, when you bored out the cats did the check engine light start coming on due to emissions? I am trying to sell it eventually and that would deter a buyer.

MJHSC400

No CEL -- Not sure why-- but like I said-- I left half of each one intact-- There are two honeycomb bricks in each one -- you can chip out the rearmost brick and the front one will stay intact--

jacobzking

my car ran pretty slow from the day I bought it a few months ago, when I did my 5 spd swap, we found a whole cat worth of debris in the exhaust, completely clogging it up. after cleaning the exhasut out, and gutting the rest of the cat and putting in a 5spd with a centerforce clutch, my car feels WAY faster. the exhaust blockage itself probably freed up 20-30hp. it was CLOGGED!

MJHSC400

Are you speaking of an SC400 or 300??

I wonder how much crap is really hiding in there--

I may have to start fabbing up a center resonator chamber--

I just want to be sure 16ga will be thick enough for mild steel to avoid a load of extra cabin noise-- I just want all the noise to be out the pipes-- There's a guy around here with a bada$$ 540i that has a gnarly a$$ exhaust note and I want mine to sound the same-- That SOB screams--