I have a 1985 Trans Am 305 carb. i just got a flowmaster 80 series crossflow exhaust cat back system put on and the thing is still as quiet as the stock exhaust!!! i was looking for more noise so i would like to put a high flow cat on. i thought about a test pipe but i dont feel like taking it on and off for inspection every year. Anyone know if the new cat will make it substantially louder? Thanks...

I have run a lot of those flowmaster systems and, believe it or not, they get louder in the first month or so after they are installed. I can't explain why because there isn't any material inside to burn out...

A high flow cat will make it louder if your current cat is plugged up some. I have had some pretty loud exhaust with stock, but good, cats...

It would probably be alot cheaper to just buy another muffler to fit in with your new pipes. Flow Master American Thunder or 40 series would definetly be louder, and you can pick them up for around $100 on Summit racing or even at the muffler shop. Best deal I've seen for a new cat in my neck of the woods is about $200 for a Magnaflow installed. Not bad idea to swap out the cat, but if you are mainly interested sound I would just swap the muffler.

i know what you're saying but we took everything off all the way up to the cat and started it up and gave it a few revs. still quiet. my dad has an f250 with dual exhaust all the way back as a complete system with flowmaster delta 40's. mine with only a cat is still not as loud. i think i might have to get a high flow cat anyway now so i dont take power away when i get a blower.........thanks!!
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good stuff...thanks!

Alright, there is some misinformation here. The only flowmaster that will work in the stock location on these cars is the 80 series, with dual exits. If you want to have a single pipe, or 2OTL exhaust, you can go use another flomaster. But dont plan on getting a 40 series and bolting it up the the i-pipe and tips of your system, and expect it to work. They are not a crossflow muffler, so you would be running all the exhaust into an outlet, and some out of an inlet. The 80-series is actually about the same baffle design as a 40-series anyway, except it is made in a crossflow configuration.

I dont see what having a high-flow cat will do for your future blower. That doesent make sense. Also, all having a cat will ever do, is quiet the exhaust and take away power. Unless your pipes are way too big and you need backpressure, but if you had a blower then the chances would be you would want to remove the cat.

That said, a good high-flow cat will be almost as free flowing as a test pipe. Not enough restriction to be worth the hassle of swapping over. However, they usually run some high dollar. A high-flow will be definately louder than a stock cat, but still significantly quieter than a test pipe too.

i was just saying for the future, ne of it is better than having a stock cat...am i right?

Yeah, but if you are seriously going to build an engine with a blower, chances are it is going to have longtube headers and therefore no cats. You would have a fat chance of passing any sort of emissions test with a motor like that anyhow.

I have a 91 305 TBI with the flowmaster 80 and no cat, it sounds like a pretty healthy 350. I'll get a sound clip if anyone wants. All my friends are very impressed with it.

so....
+1 for the test pipe

i have a 3" catco high flow cat with 1000 miles on it that i removed before I sent a car to the junkyard, just needed it for emissions. I'll sell it cheap if interested shoot me a PM

yea a sound clip would be nice...

+2

My old motor was the L03 TBI in a 91 RS. I had the stock manifolds, a 3'' catco cat (high flow) and an edelbrock RPM catback. There is a link in my sig to a vid sound clip...

I give another +1 to the high flow cat

Now, I just need to make a new clip of the same exhaust on the new L98

Bear in mind here....there is no such thing as a "High Flow" cat.
All Catalytic converters today are made with the same substrate, it's called a monolythic core.

The state here in Calif. has made Magnaflow stop putting "High Flow" on there product boxes.

Back in the old days the cats were restrictive, but not anymore. (unless one gets plugged up).

You will find out how "high flow" the cat is next time you pour some rice into your motor

On another note, isnt there a company that makes "racing" type cats, that dont use any type of honeycomb core? I think it was some type of metallic core that they use instead of the usual ceramic.

Is that cali law why they stopped marketing magnaflow and catco as "high flow" on summit ect?

I just wanted to toss in what I plan as its relative to the original posters. My setup requires something larger than 3" single. I'm running 2210 LT headers into a 3" mufflex ypipe and then into a 4" catback all the way through to the muffler. My state requires emissions for my year so I"m going to put an intermdeiate pipe where the cat is and before the test install a 3" in / out cat, then after I pass, go home and swap it out for the 4" intermediate pipe. I will NOT have my blower belt on for the emissions test or whenever the cat is installed.

I'm going to try and get that sound/video clip this week, it might end up taking till this wekend to get it, by the time I get home from work its dark.


BTW, this car is a stock 305 TBI with 2 1/4" exhaust, no cat, and not a cat-back system, I took the old muffler off and custom fabbed from there. Its a 2.5" flowmaster 80 with 4" tips. Looks and sounds awsome

I'll post that asap