Went to Exhaust shop for problem...$ Quote..

[Jon89le]

I wish my damn Cat would just make up its damn mind. Sometimes its fine and other times it rattles like crazy. It sounds as if i were to put a metal rod up against the cat while the car was on, like a metal on metal vibration. Could it be the shield got loose? Well i went to a shop around here in Delaware and the guy said he could do 2.25" piping from the down pipe, all the way back, with the installation of a new cat (purchase of not included) all for $160. It sounds pretty good to me, any opinions? I figure ill run that for now and when i do my top end swap this summer just increase the size from the headers to the cat up to 2.5.

[Mike J.]

You just made me realize that my dual exhaust on my 79 El Camino no longer makes the metal on metal sound it did for the 1st year or 2 after it was installed along with a new dual in / dual out cat. Is that 2.25" the Inside diameter or O.D. ? 2.25 O.D. is quite small (good for torque but not for upper power), especially if its not mandrel bent and runs all the way back. Each increment in dia. in a single pipe makes a big difference.

Which do you think has more flow area, a 3" single pipe or two 2"

pipes ? Answer = the 3"pipe.

[Jon89le]

The pipe would have been 2.25 inside. I still have a stock gen2 3.1 manifold so if i go to 2.5 ill loose my lowend which is all i have. The catalytic converter vibration is annoying as hell. Is there any way to remove the outside heat shield on it or no? I really dont want to buy a new 60-70$ cat when mine isnt anywhere near clogged.

[Slade901]

Two way a cat fails.

 

1. It becomes clogged solid and you don't hear rattling sounds. Too little way for the exhaust to come out. You lose power as if the vehicle would barely move.

 

2. The insides of cat breaks apart. You will hear rattling. You will have more exhaust flow but if those broken particles goes to the muffler then it will create restriction in the muffler.

[Jon89le]

This isnt a rattling though. My dads Z34 has a bad cat and it rattles. On my car its more of a vibration. As if two pieces of metal are vibrating against eachother.

[Hairdo12]

i have the same metal on metal vibration sound coming from mine... been happening for about 2+ years and it hasnt gotten worse or any better. i wish i knew what it was, if you find out let me in on it.

[Jon89le]

Are you having that vibration with a Catco cat.?