The pipe rotted off onthe side of the cat, can i plug the pipe and the hole? cant make it stick in place anymore, and I dont weld It is noisey this way.

 

The cat will burn up without that pipe. The pipe comes from the air pump and puts air into the cat to burn off the extra gases. Without it, the cat will become clogged in no time.

 

wrip out the whole pipe, and your air pump while you're at it....if you didn't know, there is an air pump that pumps air into your cat through that hose, to help the emissions.

 

Hmm, I picked up a new cat and it didn't have one of these inlet tubes... will this cat survive or does it need more o2 with the rotary exhaust? It's a 3" High-flow one.

 

man, get rid of it, no cat, no air pump

 

like darkfrost said, its for the fresh air recovery system. the air pumps job is to supply fresh air to the cat to help clean up emissions AND to cool the sucker. it is very common for the pipe to rot off. if your car is the GSL-SE, that pipe does all of the above PLUS it is the backpressure tube for the 5ht and 6th ports. without that, the 5 and 6 port wont open. they need the backpressure from that cat. the backpressure travels from the cat to the tube and from the tube into the intake for the 5 and 6 porst. repair it by welding.

 

hmm, I got a cat because I was really starting to feel those fumes eating away at my lungs... the exhaust smells so nice now i could breathe it all day... maybe even consider routing it into the cabin as a heater :P (not trying to hijack here) just wondering if more modern new cats will need oxygen injected?

did the mazda cat have the pipe JUST to help clean up the output, or was it needed to prevent the cat from burning up...

i put a 3" high flow cat on which has no oxygen pipe in... just wondering if its gonna burn up?

re Bob, if you can fix it, fix it!

 

Although I have no cats on my 7 , I thought the purpose of the air pump is to inject O2 into the cat in order to provide for a hotter burn, not cooler. More air = more fuel for the fire, so to speak.

It is the superheated cat that burns off all the little 'nasties' that our rotaries love to emit during the combustion process..

 

The cat works by heating up the excess gases that are emitted from the engine, the gases then burn off inside the cat before being thrown out into the atmosphere. The gases however, will not burn if there is insufficient oxygen. The airpump makes sure that there is always enough for the gases to burn up. If there isnt any, the gases quickly clog the interior of the cat.

 

Secondary air injection isnt anyting unique to the RX-7,many,many cars and trucks use it.The need for air injection is determined by how much oxygen is left in the exhaust stream after combustion.
Lean burning,effecient cars like modern Honda and Toyota run very lean(more air less fuel) and dont need additional air injection from a smog pump.There is enough remaining oxygen in the exhaust stream to catylize the waste products of combustion,inside the cat.
Rich running engines like trucks,rotaries or older tech engines that are still being used in newer cars,will burn more fuel due to operating conditions,long combustion cycles or flaws in design effeciency.They burn more fuel and utilize more of the availible oxygen in the intake air.Without suffecient oxygen,the catylist wont come up to temperature and process the waste.It will clog with carbon and eventually blow out or meltdown from the backpressure.Air from a smog pump is needed to supply oxygen to the cat to do its job.Rotaries leave very little oxygen in their exhaust because of their long combustion chamber and rich mixture needs.
The older rotaries without cats DID use the air pump to keep the thermal reactor cool,in addition to oxidizing exhaust waste.It had to be hot enough to do the job,but not too hot or it would melt down.A portion of the air would be pumped around the outer jacket of the reactor and then dumped out a small exhaust pipe that paralled the main exhaust pipe.

 

Thank you Steve, You killed two of my birds with one reply. I also have a RX3 to restore. Again Thanks. And the rest of you all too.

 

So If I dump the cats and weld a straight pipe (which Im about to do) in its place my 5th and 6th ports wont open? We have no emission laws here in AL thankfully.

 

What about this....I changed from stock exhaust w/ pipe from air pump to cat to RB full exhaust (Off road use only - of course ). I don't want to get into removing air pump at this time, I plugged the rubber line at the engine.

My question is, if that feeds air to the cat, should I have plugged it, should I unplug it now? will it damage the air pump to be pumping against a plugged line?

 

Its pretty low pressure,but it may be possible to damage the airpump by deadheading it.If its not too loud,Id just let the airpump run open for now,until you remove it.Dont want to strand yourself if the airpump does protest,it could blowout your fanbelts if it pops.

 

Yeah, I was thinking along those lines too. I just don't wanna dig too deep an emissons hole should I need to smog it in the future...