Catalytic Converter Question
 

I do not have to pass an emissions test or anything serious. I was looking at high flow cats mostly to "febreze" my exhaust some without severely affecting the flowrate, and at the same time not melting from the heat.

Is there a high flow cat that will work on our cars without having to pump fresh air into them, or will any high flow cat work?

Does it have to be bolt on or are you willing to get it welded in?

I would most likely have it welded on as the rest of my exhaust is welded together.

Would one like this http://cgi.ebay.com/ebaymotors/ws/eB...K%3AMEWAX%3AIT last any amount of time (1.5+ yrs) behind a turbo rotary engine?

Magnaflow makes a metallic catalyst that is high flow. They are selling them at summit racing for 95 bucks.

I am wondering the same thing,
Can you install a Catalytic that has no Split air on the cat and will it Suffice as far as Emission "police" are concerned?(no air pump installed?)
We have Vehicle inspectors that will Stop cars and look at emission stuff.

that sucks vehicle inspectors? in mass rx7's don't go through any emission tests.

Google up bonez catalytic converters... They are made for rotary engines. They even work on full bridge motors without melting or failing. Check it out

I checked out the bonez cats. Read several good things about them. I read several positive results from people running them. From what I read I believe they were all running an air pump to it.

Reinstalling the air pump is not an option for me, as I have tossed the "rats nest" and I have no intentions of replacing, reinstalling that mess of stuff.

Has anyone tried one of the less expensive cats without air being pumped into it, and had it last longer than a year or two? Again I have no intentions of putting it up against a sniffer, other than the one on my face. :)

+1 also.
I do not intend to have the car smogged as it doessn't warrant it any more due to the year..But if it is Viewed by EYE,I am hoping just the Cat on will suffice.
I've seen some Racing cats too,,look like a Big Bullet.Hi heat metallic substrate thingie.
I also want the Car to 'smell better' from the tailpipe,That right there would be helpful if pulled over by the inspectors.

AFAIK you can't run a cat without an air pump. You'll destroy it after a few months-ish. Rotaries especially (but also pistons) run slightly rich by design so that the excess evaporating fuel can cool the intake charge and prevent detonation / knocking. A little gasoline is a much more convenient cooling mist for the auto maker than creating an extra water tank, though some extreme performance turbos inject water or alcohol. Sufficient air must be added to burn the extra fuel. This is basically what the catalytic converter is for; to burn away the excess fuel (hydrocarbons, HC) and partially combusted fuel (carbon monoxide, CO) quickly with a catalyst rather than a higher temperature, slower flame. The pollutant NOx reacts similar to oxygen. Without sufficient oxygen you'll screw up the catalyst with all the excess unburnt hydrocarbons and it'll start breaking off in chunks. Not to mention it can't possible burn up pollutants in the meantime without the air to burn it with, even if you could somehow find a cat that can survive without an air pump. This is also why some cars can shoot flames out the tailpipe; the unburnt crud finally gets some air and burns. But without a cat it is done poorly and is still loaded with pollutants.

Looks like the there aren't many options. Without air pumps, RX7's tend to eat up cats. I don't know if it would make a difference, but you could always try installing a high flow cat further down your exhaust if you're running single exhaust..

Okay I'll just save my money and have a smelly car. :)
Thanks for all of the insight.

i have a smelly cabin and its just fine :)

If you have a smelly cab you should try replacing the shifter dust boot. Makes a world of difference in terms in-cab smell/noise.

yeah it needs to be replaced..its in 2 pieces and not even bolted down anymore

Quoted for truth. Replaced my shifter boot because my old one was in a million pieces and the cabin smell went down quite a lot.

The molybdenum disulfide used in gear oil does smell nasty.

I need a new dust boot too.

hey just wondering, can you just take a small bar or pipe and stab through the cat converter? I did this to a 69 road runner and somehow it passed emissions and made it run a bit more beastly. haha if so i would like to try this on my rx7 to see how it runs. my cat is toast anyways. I still don't know how it passed

69 road runner should not have had a cat on it!

if you have everything right you can pass the high speed part of the emissions test with no cat, but it'll fail the low speed and idle.

I've stumbled across this thread as I am investigating a new cat for my 13b turbo. There are a few mentions here about longevity of a cat behind a rotary in the absence of an air pump/air pipe.

I have been using the same 3 inch cat in my car for 14 years and it has never had an air pump and it has been and still is working fine. I am looking to swap it out just because of the age.

Arran

Depends on the cat. More modern high flow metallic cats run fine without an air pump if the car isn't dumping fuel into it. That's half the problem with the stock ECU. Mazda's mentality was "when in doubt, more fuel!".

Oh and to the person who says the Bonez cat will function behind a full bridge, please send me some of what you are smoking. I'm not sure if you don't understand bridgeports, cats, or both. ;)

This raises a good point in regard to proper AFRs in tuning for longevity of our metallic felines. Suggestions on this one, Aaron?

Hmm, I think I prefer the term "iron pussy" to "metallic felines".

As for the correct AFRs, that's easy. Keep it at 14.7 as often as possible. Obviously that can't happen all the time. For example, in boost. Or just after cold start. Batch fire or poor resolution standalones probably can't achieve this at idle either (or if the engine is ported). However cats can tolerate much richer AFRs over the short term. But if one is running around with the AFRs in the 12s (and it's amazing how many rotarys I see "tuned" like this) then the poor little pussy is going to die a quick and stinky death.

Most modern cats will tolerate leaner ratios because of fuel economy requirements. So 15.0:1 or even a bit leaner (depends on the cat) would be fine if EGTs are in check. Some OEMs drop timing and lean out the ratio in cruise for this purpose.

Now an air pump will be needed if one expects to get OEM life of 200,000 miles out of a cat. The air pump keeps the AFRs heading into the cat as close to 14.7 as possible in situations where it just can't be regulated that lean by the ECU. During WOT, cold start, and idle. This is something I am constantly waffling about on my Cosmo. Whether to have an electric air pump (Corvette) switched on my the MS3-Pro when the AFRs are richer than about 14.0.

the problem with the pre-MSP rotaries, is that they cannot be run at 14.7:1 at low rpm without misfire. a misfire = higher unburned HC's than running a little rich.

so they add the airpump, which adds air to the exhaust ports when the engine needs to run rich. if you refer to the manuals, you'll see that the air pump air is dumped in the the atmosphere after ~2500rpm.

the MSP engine has less overlap, and can be run @14.7 at idle, so it only has the airpump run for ~30 seconds on cold starts, like every other car.

the other issue is temperature, the cat only works in a certain temp range, and thus most OEM's try to get it up to temp as fast as possible, which means running rich, with retarded timing and an air pump, and at the other end, they run rich in order to keep EGT's down.

the Rx8 has "EGT" and it basically keeps the cat around 650c, give or take. and if you put an EGT probe on a stock S5 NA, you would find that it idles around 550c and has a peak EGT of about 720C.

modern three way cats need to be cycled either side around the optimum stoic to regenerate the catalyst

if the cat is run too long lean or too long rich then parts of the cat become saturated and it no longer can perform all three functions ( CO, HC and NOx reduction )

modern engines will have a strategy to deliberately bounce the AFR rich or lean for a period to regenerate the cat
sometimes using a flag from exhaust temp or even from dual 02 probes

in FC's for oz and the US
mazda used a strategy with the cats being broken down to a pre cat with two dual cats
each part having a job
taking inputs from exhaust tip temp and the running condition of the engine
( ie. decel, warmup etc )
the airpump direction is altered
( either to the exhaust port. or after the reduction stage of the cat or dumped to atmo via the moo )
in conjunction with the fueling strategy ( ie, rotor fuel cuts on decel etc )
to help regenerate the reduction side of the cat and to reduce the EGT seen at the rear pipe
( ie air pump directed post cat )

when the condition of the cat was considered optimum , the airpump ACV would direct the airpump to the moo ( atmo )

when the conditions for the cat where considered too reducing
then the air pump is directed into the exhaust port to encourage oxidation to occur earlier and regenerate the oxidising cat


clearly, very few of you are going to build all this strategy into your ecu's

as such , tyring to get something to pass a modern im240 test

then it may pay to build the cat a little further back in the exhaust stream
where it is protected for the extremes of temps seen in vehicles without a cat protection strategy

and direct the ( electric ) air pump permanently into the exhaust ports
( via a fixed ACV ) where it does the most work reducing HC

and when exhaust temps are deemed excessive , turn off the electric airpump to reduce nox and allow the reduction cat to regen
( and run lots of ethanol in the fuel during the test as it both leans the same injection period down whilst burning at lower temps and naturally reducing the NOx production )

doing this emulates the original 2 way cat strategy , but doing not lots of favours for the NOx part of the cat
( for which we used the more friendly ethanol blended fuel to help bandaid through the test )