I just bought a 84 rx7 and I got a muffler shop to install a universal muffer that i had bought, I was expecting to get my car back and sound Loud.. Thats what i want anyways ... Anyways after the Big Cannon i bought was installed it sounded no louder then stock, Im pretty disapointed!!!!!!! how can i make it sound louder but still keeping it legal? I kno there is 3 cats but do i need them all? K thankz

 

Well, if you want loud, there is a simple solution-get rid of the cats.

Of course, this is NOT legal. But, you can get a cat replacement pipe, it will be loud (too loud in my opinion) and you may even gain a little power out of it. I don't know how it works in Canada, but here in NC I run year round with the straight pipe, and just put the cats back on once a year when it's time for inspection. However, I do wish my car was much quieter, but I really miss the extra HP my car gets without the cats.

A halfway point would be getting a high-flow cat instead. That would keep you legal (and in all likelyhood, the new cat would clean better than the old one), boost performance a bit and still be louder.

 

The plain fact is that cats act as mufflers. Replacing a muffler that isnt that restrictive with one that is larger more straight through isnt going to produce much. Depending where you are in bc, aslong it isnt on the main land, you should be fine with just a straight pipe. prepare for it to be LOUD. Get a resonator or glasspack between your muffler and your exhaust mani. it will help lots.

 

A good deal of the exhaust noise is suppressed by the stock exhaust manifold, then the cats. If you remove those and add a header, it will be very loud, annoyingly so, you will need a pre-silencer or aftermarket cat, designed for rotary heat, to bring the noise down to tolerable levels.

 

alright thankz, i will probaly start out by putting a header on and go from there. Any recommendations on a header? or a good place to get one from?

 

www.racingbeat.com

Probably the only header you should use in an RX-7. Just keep in mind you'll need to get the presilencer with it too if you want it to bolt up to the stock locations.

Once again, I don't know how it is where you live but a header is definately NOT legal in most states here in the US.

 

Now you guys have me nervous about removing my cat. I have a glass pack where the factory muffler was, as the original post said, not very loud. I wanted to take the cat off because it is still the factory original. I am not too concerned with the sound in the car, I have a loud enough stereo to get over that, but if I am going to get pulled over for it being too loud then I may have to reconsider. I have factory manifold, factory cat, factory pipes, and the glass pack, which doesnt even have a tail pipe on it, just sticks out behind my bumper. How much louder would it be if I pulled the cat out and put a straight pipe in there? Not that I would.. cause I live in Michigan.. and removing the cat would be against the rules...

 

If your model is an SE with the 13B 6-port engine, backpressure is needed to activate the 2 intake ports at high RPM. If you go with a straight exhaust you'll need to modify this to work correctly.

 

oh yeah, I guess I forgot the details. It is a 83 with the 12a motor, no fancy stuff.

 

To improve my present worn exhaust system, I am thinking about retaining the stock manifold and eliminating the 2 small cats ( the large cat has been removed).
There is a stock muffler at the rear and it is quiet.

So what is more restrictive -the cats or the stock exhaust manifold?

What geomtry or whatever is in the manifold that makes the header so much better? (I have not seen one yet)

 

Headers seperate the exhaust flow between the housings, allowing for better flow. The stock exhaust log collects both exhaust ports and allows them to bounce around inside the log with each other. This cancels some of the noise by mixing the sound pressure waves, at the same time it restricts flow.

I had a car in the shop yesterday that had all 3 cats removed and straight piped. Stock exhaust log and muffler were still in place. Car was very quet, much to my suprise.

 

^^^yeah i have that done to my car its still quiet