I just bought an '87 Firebird, in terrible shape (it was neglected for six years), and they removed the catalytic converter when it clogged up. They put in a straight-pipe, but MAN it sounds terrible, it's more blatty than my GTA... I'm going to replace the converter, there really isn't an excuse not to run emissions on a street car anyway. Maybe I'll get a new muffler while I'm at it, the one on the car now is sick. But not until after I put Edelbrock's cat-back on the GTA!

 

There's a lot of factors involved when it comes to exhaust sound. Like manifolds or headers, size of pipe, muffler, and the cat. This may not be helpful but this is just an experience of mine; my coworker had a 5.0 Mustang with duals and some nice Flowmaster mufflers. He tried using bogus cats (straight pipes) and it sounded like a nasty truck, so he put the cats on, and it had that nice mellow rumble and growl similar to many f-body cars with healthy exhaust. I hate the nasty work truck sound (straight pipe or cut-out plate, don't get me wrong, cut-outs are cool, but sound gross sometimes. Just because it's loud doesn't mean it sounds good).

 

I have the hollowed out cat myself and it's definitely louder and sounds good when I'm revving the engine. But for some reason, when I get up to 3rd or 4th gear it almost sounds like an exhaust leak. It's got the tiss, tiss, tiss sound. Although I do know I have some older injectors but I seriously doubt that could cause that much noise. Also, I can't really climb under the car while I'm moving to figure it out.

 

I have hooker shortie's high flow cat and 3" flowmaster american thunder cat back and it has no deep growl at all when i had no cat in it, it sounded alot cleaner than with the cat.

 

hot 69z, i have the same setup.

are you saying it sounds better or worse without the cat? it had no growl without the cat?

your post is not clear to me and i was thinking about removing mine and putting a str8 pipe.

 

what i mean by growl is that with the high flow cat the exaust was very tame.

Though it sounded excelent at idle as soon as i put my foot into her she sounded terrible. I don't know how else to explain it.

 

So it sounded better without the cat?

 

in my opinion it does differnt ppl have different tastes tho. for me it was very crisp sounding at idle with the cat but when reved up it wasn't as crisp. when i took the cat off it was crisp sounding at all RPM's. I wish i had sound bits so you could listen to the difference of my car with and without the cat.

maybe someone in the sound board has a sound byte of the car with and without the cat

 

Thanks!


I also have the american thunder catback. I am pleased with it, and its pretty damn loud. I am adding headers and a 3" ypipe. I am debating if I should leave the cat, or run a straight pipe through it. I like loud, but not a raspy metal sounding loud.

 

Took a few posts to understand what you were saying, glad it's clear now. No cat = good sound.

IrocThe5.7 - Exactly, I'm trying to avoid the bad sound and gain some power.

Clear on the first part now, not sure if it's going to add any power.

 

if it makes any difference when i switched out the cat i didn't notice much power difference till about 4500 and i definatly had more low end with the cat that i do without