I have a 305 5.0 and I was thinking about replacing my stock cat with a high flow cat. I have a flowmaster exhaust and wanted to make it louder. So would the high flow cat help out to make it louder?

 

Are you obsessed with Making LOUD noise with your exhaust when the car is a slow dog.

 

Sometimes it is better to look good than to feel good. If he wants to make noise let him. When it comes time to back it up, that will also be up to him.
I had a friend with a 72 Dodge Dart and his dad basicly made him a cherry bomb muffler. The way these imbreads tuned thier cars was horifying. He had a slant six and it sounded like a 440 with a cam. One day in high school some people wanted to see what he had under the hood. I warned him not to open it but he did not listen. You never saw people walk away so fast in disapointment.
I also saw a Areostar family van with an import exhaust on it. At least a V8 Camaro is more deserving.

I would not count on a free flow to make it very load

And I dialed in at 15.5 at the wednesday drags in my 84. At the last race of eliminations I was so far ahead of the 70 Chevelle I braked hard before crossing the line, did my 15.5 and got me a trophy!

 

Highflow cat + flowmaster has so far been the best improvement I’ve made to my car as far as sound goes... with a stock midas muffler and orgional cat all you could hear going down the road was the engine fan. With just the flowmaster it made hardly any difference in the sound area...but after the cat it actually sounded like a V8, more than likely because the 23 year old cat I had on there was clogged up...
If you want a nice cruzing sound and having a ton of power isn't something you are really dying to have or able to afford I highly recommend a high flow cat w/ your flowmaster.

But we might have different opinions... If you want your car to sound like a 454 with heads and cams when it only has a 305... well that just isn't going to happen.

 

I find that about 90% of all the cruisers want a tough looking and sounding ride and NEVER see the top RPM's the engine COULD make--It's all image.
Now to a real question: with a dual system, you want a crossover for power, With a modern Y pipe system, how much power do we lose--if any for joining the sides together with one Cat--no matter how big? I guess it does serve somewhat as a crossover but how much is too much?
Roar

 

If you just want louder, you might look into getting yourself a nice flowmaster based true dual with an X crossover (H pipes are evil, like side post batteries...) and a couple of high flow cats to go with it. You should get some decent, if not entirely worth the money, power gains from that as well. If that's not feasable, though, the high flow cat might make some difference, though how much can be attributed to the high flow aspect, and how much is due to just a new cat with clear passageways is debatable... In any case, good luck in that pursuit of muscle car image, and don't show it off to the wrong people.