All,

Has anyone actually had their high-flow cat clog because of a removed air pump? I know that everyone has heard that it will clog, but are there any first-hand witnesses to this effect?

I've heard:

* Removing the air pump will make the cat run too cool, clogging it with unburnt fuel
* Removing the air pump will make the car run too cool, clogging it with oil from the oil injection system
* Removing the air pump will cause the EPA to break down your door with a battering ram

But seriously, I'm just having a hard time believing that the cat will run "too cool", especially when you get rid of your pre-cat. The exhaust temps of the rotary are so high that I doubt the air pump is really necessary.

So I'd love for someone to prove me wrong and tell me that their cat clogged after the air pump was removed!

-ch

 

Its not the heat range thats making it less effective, its that there is more Oxygen in the cat with the air pump working, making the reaction more efficient. Still, hotter temps would help this, but who knows! I sure as hell dont.

 

i think it depends on what cat you get

some cats will clog soon after you get them even with the airpump

the Bonez high flow is by far the best and only way to go if you are getting a cat
you won't believe the power you gain with a midpipe if you are allowed to have one that is...

 

I had the same question the other day, im running the stock cat with no smog pump, and a catless downpipe. with the rediclously high egts of the rotary and exhaust velocity i just dont think its gonna happen. anyone with a fd had this happen?

 

stock cat is way too big. I think it's more likely for the stock cat to clogg up rather then the hi-flo.

 

the stock cat will clog without the air pump, but it takes quite a while. remember that the air pump only runs below 3000 rpm anyways.

 

I ran my HF cat for 2 years without the airpump running a constant 350+ rwhp and never had trouble. Funny thing was I had Meineke weld their performance cat onto a midpipe I had and it worked awesome. $150 installed....please don't tell me that dropping $300-450 on a HF cat just because it is a "Bonez" is worth it because I have yet to see why Bonez is better than my cheap one that is supposedly not able to withstand the heat of a rotary...just another gimmick for companies to take your money.

 

I was running a stock cat with no air pump for 3 years, and when it was replaced the car wasn't showing any signs of any kind of defect.

 

Did it still pass emissions testing w/o the air pump? Or did you not have to be tested in PA?

 

My HF cat exploded on me .......

 

Since we are on the subject of the airpump... should the car idle differently when I unplug the airpump? I was messing with it the other day, and when I unplugged the the grey connector, nothing changed. I didn't check to make sure the pump was still pumping, but the engine didn't seem to notice the difference.

 

From what I have read in the past some cars do and some cars don't.

 

What in the Hell is a "clogged cat" and how in the world can the lack of an air pump cause this? Seriously? Can someone please explain the mechanism how this would occur? I'm talking about the "main cat" here, not the "pre-cat". I'd love to see a picture showing the insides of a "clogged cat". This sounds to me like one of those "urban legends"!

The catalyst is commonly a honeycomb type structure with platinum based catalytic material on the surface. The honeycomb provides the passages where the exhaust flows and comes in contact with the catalytic material. I've heard of catalyst failures where the substrate (honeycomb) collapses and you can hear it rattle around. I suppose that a substrate failure could possibly occur in such a way as to restrict flow somewhat but it's not obvious to me that it would result in "clogging" the catalyst.

To me the term "clogging" means the catalyst has failed in such a way that severely restricts exhaust flow more than what naturally occurs by a correctly operating catalyst.

The only exhaust system "clogging" I have ever seen to be true involved those old "glass pack" muffler systems.

 

https://www.rx7club.com/forum/showth...hreadid=227840

 

Like I said, "I'd love to see the INSIDES of a clogged cat."

I saw that link and picture before posting my comments. Just a bunch of loose crap from a collapsed substrate like I have seen before. I want to see how this stuff "clogged the cat".

 

That link is a picture I posted and the debris in the lower right corner IS the insides of the cat!

The "bricks" inside are a honeycomb like structure that exhaust flows through. The bricks crumble and then the bits get packed together by the exhaust pressure. The wire mesh is what holds the bricks in place inside the cat. If you look inside a clogged cat it's quite obvious when it's clogged!

My cat failed while I was at the track. Car always had a 10-8-10 boost pattern and in the third session of the day I noticed the boost appearing to be low. The primary would boost to 10, but the secondary would only do 9 psi. Then 8 psi a lap or two later. Then 7 psi. Then about 6.5 psi. The brick crumbled and then it just got packed tighter and tighter and therefore clogging the flow. The primary turbo acted fine the whole time. A clogged cat is like a clog in a drain. As long as the flow is not enough to back up behind the clog, everything is fine. Once flow increases the clog backs up. There was not enough of a clog to hinder the primary, but the secondary was having a tough time.

Removed cat, saw clog and replaced with a new cat. Problem instantly solved and car back to normal. I can assure you that the cat can clog!

As for clogging due to lack of an airpump I can't say firsthand. The air pump injects air between the two bricks inside the cat and so aids tailpipe emissions by ensuring the additional burning of any fuel in the exhaust. The reason Mazda switches the pump off at higher RPM isn't because it's no longer needed, it's because Mazda knows the Feds only check tailpipe emissions at lower RPM. If the lack of an air pump contributes to cat clogging I dunno, but seeing how sooty rich rotary exhaust is I could see how over time the "holes" in the brick could get clogged.

 

I've had a few discussions with mjw on the subject of airpump/hi-flow cat... he called a couple of HFC makers, and some said that it was necessary for our cars, while others stated that it was free-flowing enough not to require one.
Your best bet is to call/email the manufacturer of the HFC that you want & ask

 

This is the subject of this thread, and this is what I am questioning. I suppose if a car "continuously" emits sooty rich exhaust that might cause a clog over time. But who is driving around with "continuous" sooty rich exhaust?

A temporary, short burst of sooty rich exhaust may accumulate somewhat in the catalyst but will quickly get oxidized by the catalyst itself. My point is that I've never seen an intact "clogged catalyst substrate".

Your picture shows a "collapsed catalyst substrate" which I personally believe has a lot to do with poor initial construction of the catalyst, not your operating parameters.

 

You may very well be correct. My main cat was original and lasted over 110,000 miles before crumbling; seems like its "life" was just fine.

As for an intact catalyst that is clogged, I don't know of any first hand. But then again that may not happen; they may all clog due to crumbling.

 

I don't know if running without the air pump clogs the cat or not. And I have long been leery of the claims that it does.

In thinking about it, I do have a scenario in mind that could clog the cat. With the air injection, the temp may be kept high (since adding air may promote additional burning). That may burn off some goop that may otherwise accumulate on the cat innards. I have no idea if this is what happens or not, but it seems like a possible scenario in which not running the air pump might clog the cat.

Cases where the innards break up may be related to the kind of clogging I am speculating about here. For instance, if the cat gets clogged in some areas and not others, or if it starts to run hot after clogging and it is too late to burn off the goop, that may cause the honeycomb to fail. But it could be something else entirely. When the core does collapse, that seems to cause clogging, but it may be a different kind of clog than simply running without an air pump for a while.

That is all speculation. It would be great to hear from someone that has real knowledge and experience in this area. I don't have that knowledge or experience, but I just wanted to share some ideas about what may lead to failure. Though I personally don't believe the FUD surrounding failed cats and running without an air pump.

-Max

 

The question is why would you run a hi-flow cat without the air pump?

The reason to get a hi-flow cat over a midpipe is primarily for emissions compliance. Well, you won't pass emissions without an airpump, so IMO, the situation shouldn't really exist in the first place!

 

Here in Missouri they do visual inspections, and don't do tailpipe emmisions.

You can pass the visual inspection without the air pump on the car, but they need to see a catalytic converter to pass you.

 

You guys keep talking about the air keeping the temps in the cat high, but just by removing the precats, isn't a ton of heat going right to the cat? Especially so if the DP is wrapped.

 

I really think that the primary purpose for injecting air into the catalyst is to provide more oxygen which promotes more complete oxidation by the catalyst. It is the more complete oxidation which will cause higher temperatures in the catalyst, not just the injection of air.

 

I think that much is obvious. Air from the airbox is not going to raise the temperatures by itself, but we're talking about exhaust gas temperatures so high that titanium manifolds warp. The precats never needed an airpump.