Got a Flowmaster 80 catback for free from a friend, and I was just wondering what I should do with my cat? The current one is stock with 180,000 miles on it, therefore it's taking the trip. Now I know alot of people say we need backpressure for our v6's but is anyone running no cat? I am probably gonna go with a high-flow, but I wanted to see some of you guy's opinions.

BTW, 91 Firebird 3.1

 

Two options:
(1) New cat..a high flow Catco seems to be the general choice. Mine worked just fine.
(2)Run cat-less...BUT, do not simply 'gut' the catalytic converter and leave it on there. Either cut the cat and get a converter delete pipe, of the same diameter as your exhaust piping, and run it in the place of the cat. If your catback is 2.5 in, which I assuem it is, you'll need your replacement pipe to have a 2.25 in. inlet and a 2.5 in. outlet. OR you can just run this pipe THROUGH the inside of the cat...so it still LOOKS like you have one on for visual inspections. You should be running just fine with a pipe..just make sure you have a pipe there. Hollow cat = air expansion chamber...creates turbulence and adds backpressure to the exhaust.

 

BTW the catback came off of a 4th Gen V6 and is 2 1/4 tubing.

 

You sure it's a catback? Sounds like a muffler and factory piping to me... I doubt any performance catback, especially a Flowmaster, would be 2 1/4 in...too small..

 

Yes, I'm positive.

 

Sounds to me like a flowmaster muffler and stock I-pipe.

I had a pipe in place of my converter, but it was like that when I bought the car. It did sound a little deeper than my friends with the stock cat.

 

Did yours sound bad (*****) above a certain RPM. I know it's gonna be nearly impossible, but I want to try and avoid that if possible.

 

Flowmaster on a 6 sounds raspy... Not much you can do about it...it's the acoustic characteristics of the muffler.

 

You have a stock 60* 4th Gen "Y" pipe & CC?
How will you attach it?
Is it a direct fit?

On my 85 Blazer, I have a Flowmaster Two chamber (2 1/2" in to two 2" out pipes). Have for 9 years, now. It's ok, but a bit loud. It'll now be behind a 3.4 mill so I hope it'll sound smoother.
I got a ticket once, cop was a pig. They stole my $90, fu(kers.
Power increase from the cc/muffler upgrade, DEFINETLY!
Really opened up the top end power on my Truck. Before I was able to get to 75MPH top speed. After I was done I was able to go up to 90-95MPH and then hit a wall.
Now with the 3.4 power, I'm curious...... I can so feel the 200 foot pounds torque just lurking to be used in this Blazer conversion. I like that feeling.

 

Nope, everything is stock 3rd gen. exhaust currently. The only thing that is 4th gen is the catback and it is not installed yet.

 

I would go with the Catco or some other type of aftermarket cat replacement, especially considering the mileage on the stock one. I wouldn't go 'catless' just to keep the thing on the legal side, and in case you ever sell it, it won't be a problem.

 

Damn good point, thanks.

And thanks to the rest of you guys that replied.

 

My muffler was not stock, but it was an oem style replacement that the previous owner put on. In my opinion, it sounded GREAT after 4000, all the way up to about 5700 or so. I used to rev it up all the time. And the lack of a cat added a little more of a gurgle sound at idle than what I heard on my friends 2.8.

 

Cat Convertors definetly act as muffler resonators.

 

Not to mention silencers.