You've probably heard that not having A.I.R. will ruin or clog a cat (I've heard it several times on this forum). I won't repeat the whole story, but here's a link to my "rest of the story". https://www.thirdgen.org/techbb2/sho...53#post1565753

Understand, I'm not advocating not running A.I.R. (I'm sure it makes the cat work better). I'm just trying to dispel one more wive's tale.

 

I think advising people to run the air is important, just because we can't be sure that in every case they'll have good results doing otherwise. You know a lot of the people on this board aren't running quite as clean as you are, and I don't doubt that air may sometimes prevent problems for them (clogging or otherwise).

 

I've spoken to a few catalytic converter companies on this, and have gotten the same answer from all of them. If your exhaust temps are hot enough (i.e, wrapped or coated headers, high output motor), and the cat is close to the engine then you won't need air. You'll get slightly higher emissions, but it will be ok.

But if your exhaust is not very hot, and the cat is far enough back than the lack of air aiding the catalyst will result in an incomplete burn inside the cat, resulting in carbon buildup between the combs.

Another note: a cat designed to not have air flows more than a cat designed to have air. why? 3-way cats have 2 combs, 2-way cats have 1. Inbetween the combs is the air rod which causes turbulance, in addition to the turbulance of the air leaving the first comb and having to go into the second.

So your absolutely right, to a degree. I'm sure most anyones slightly modified, or even stock car puts out enough exhaust temps to do a complete clean burn, but there will be cars out there that don't fall under the same conditions.

-- Joe

 

And I suppose I shouldn't try to apply my experience to the entire world. But, I've heard several people insist that if you don't run A.I.R., you'll end up with a plugged cat in no time.

I'll gladly accept the "high output motor" designation, though...

 

Which is why I got on the phone and started calling everyone, researched the topic. I really wanted to know. The carbon buildup is from unclean and incomplete burning in the cat. Air aids that, but every cat company I talked to told me "If your cat is close to the engine, and its a modified engine its putting out enough heat; than its possible to delete the air".

So on my supercharged 355 w/ the sportsman II's we're talking serious heat.. On a 8.6:1 305 I'm almost positive a problem may develop.

Heh..

-- Joe