The catalytic converter on my 83 Rx-7 has a hole too large to patch. Since I live in a state with no emissions tests, I was wondering about the pros and cons of eliminating it---aside from any environmental effects.

Bayou7

 

The cat convertor is there to control emissions. Nothing else. Since your state has no emissions tests and assuming you're not a tree hugging hippie with rainbows and peace signs and **** painted all over your Rx-7 then there are no cons in getting rid of it. The pro is a better flowing exhaust system and better performance.

 

I read somewere that first gen require back pressure to activate the secondaries on the carb. I dont know if that is true or not but if it
is than lack of back pressure may cause a problem

 

Um, no it's not true. Where did you read that from? The less restrictive your exhaust is for a given primary length and pipe diameter the better.

 

So are you saying if I ran some straight pipes out the side of my engine bay I'd have more power and my secondaries would still open? Cool... hehehe

 

Bayou7 I have a straight piped '83 GSL, because the small and large cat were clogged. Well, at least I think there were...hehehehehehe. It runs great and I noticed a performance difference for the good after doing it. You may want some type of presilencer on it if you don't want a loud car. Racing Beat I know offers some good products. By the way, don't get a Monza muffler or Pace Setter header.

 

Not exactly. Your primaries still need to be the correct tuned length which varies depending on what sort of porting you have. I'm not sure what the right lengths are for different engines but most good street exhaust systems collect the primaries just before the rear axle. Though I have heard of some people running seperate primaries all the way to the back of the car. As for the carb secondaries, they have nothing to do with the exhaust. They operate on vacuum.

 

the things you heard of that operate on exhaust backpressure are the aux ports (called 6-ports) on the 84-88 N/A 13B's (the 89?-91's open with a RPM controlled solenoid affair). You don't have to worry about those unless you have a GSL-SE.

Even w/ a -SE, a straight pipe exhaust will work as long as you have a muffler and pre-silencer. They only take about 3psi to open, and you could either wire them open or rig the airpump to feed them pressure like some of the second gen guys do.

--matt

 

Thanks for all the feedback. I have a Monza exhaust system, so it sound like if I pipe straight back to that, it shoud be fine--- even better. Great!

Bayou7

 

It'll be fine, but it'll be LOUD! Also, dont expect your Monza muffler to last very long. It'll keep getting louder and louder and louder...

 

If you replace the cats with a midpipe do you have to do anything to the airpump? My airpump is still there and the sound kinda pisses me off. To remove the airpump what else do i have to do? I've heard of some dual pulley thinger.

 

if you want to go all out racing beat has an exaust that elimenates all your cats and the thermal reactor (stock header/cat) and puts headers to pre-siclencers to an up graded muffler add lots of HP and raises hp 25% after 7k rpm's

 

they don't check if you have the cat converters, because were i live, they don't put the thing on the muffler, but they check for the cat converter.

 

Winnepeg,
If you take the air pump off, you need to replace the alternator pulley with a double sheave pulley. See Racing Beat. You need to get a "matching set" of belts. NOT just two of the same belt. They need to be ordered from the manufacturer that way, or if you have a local manufacturer they can do it for you. I have heard from one guy that he had good luck with the Mazda factory replacements that were not matched though.
If you do not replace the pulley, you run the risk of "belt squeal" and water pump cavitation at 8k rpm. I had the problem with the belt squeal.
hope this helps
hanman