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I was given a monster cat from a turbo car, a Mitsubishi EVO which had its exhaust upgraded.

In common with most (all?) turbo cars the pipe is significantly caked with thick black soot.
I understand Turbo/Detonation/Run Rich for safety is the scenario that leads to this.

On a technical level, how the hell can the cat still do its job under the circumstances?
If this rich layer of soot renders the cat inoperable that would mean most if not all turbo cars are illegal in an emissions sense.
At the very least the thick soot on the screens would render the air flow less efficient.

Can the cat screens be cleaned?
How do you test the efficiency of an old cat? I would imagine that some sort of exhaust gas analyser is used, not sure how difficult it might be.

In the same path of questioning, how does the NB, SE, SP exhaust sensor (O2?) and ECU interact with the cat?
An exhaust fabricator told me the car would run crap without the cat, not that I am thinking of deleting.

I have searched this forum without luck, so hope some of the engineering/tech genius's can provide answers.

Vehicle exhaust emissions are measured over a drive cycle that all but the most underpowered vehicles can cover at part throttle.
Most modern vehicles use 3-way catalysts that only achieve the reduction of all 3 regulated toxic gasses when the air-fuel ratio is near Stiok.
At heavy loads, the engines run rich of Stoik and the catalyst gas conversion efficiency is low but this is outside the regulations.
At lower loads, the catalyst will still run hot enough to burn off the soot (if it is not to much) and regain conversion efficiency.

I do not recommend trying to clean the catalyst because you will probably damage the surface coating that gennerates the catalytic reaction.

Swapping catalyst from one type of vehicle to another may result in non-compliance. Vehicle manufacturers try to use the cheepest catalyst thay can to meet the regulations for 80,000km. As a result they will match the washcoat, catalyst possition and engine calibration.
After market catalysts tend to have lower loadings than thsoe used by vehicle manufacturers (ie. even cheeper) and may only comply when new, if at all.

The only way to confirm emisson compliance is to run a proper test on a rolling road dyno with the appropiate analysers.
Portable analysers can show if there is some activity in the catalyst if the catalyst is warm (drive the car first and stick the analyser up the tail pipe immediately you stop). Similiarly, maesuring a temperature rise of the exhaust gas passing through the catalyst will indicate some activity (the chemical reaction is exothermic).

I've got a stock Evo 6 cat lying in the garage trying to rust.
Never give it away as they have scrap value due to the platinum in them (never heard a wrecker buy them though). In America people steal cats from parked cars (4wds as they're higher).

So even though it has crap on it the cat may still work, but even if it didn't, who would know or care?
This one seems to be massive with 3in outlets. It might be interesting if I ever turboed the car. I don't see a NA car needing anything this big.

What about the car running poorly without a cat? Is that a load of hogwash?

My understanding is Some cars have O2 sensors or similar after cats, so if the exhaust gas isn't clean enough it hobbles the car.

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sailaholic wrote:My understanding is Some cars have O2 sensors or similar after cats, so if the exhaust gas isn't clean enough it hobbles the car.

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But not applicable to MX-5's ?

Not na, don't think nb. Can't comment on nc.

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Car should run OK without one (see racecars) but it has all the negative effects for the environment. As long as it's not a restriction in your exhaust I can't see a larger one would be bad unless its not coming up to temperature.

I've always just fitted new ones when changing exhaust and not thought more about it.

The NA has what looks to be a temp sensor in the cat. What are people doing for aftermarket setups?

I think that is jdm cars only. My guess is remove it and the light in the dash :-P

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I just cut one off a stock cat and rewelded it to a custom mid pipe i made.

Dann

NitroDann wrote:I just cut one off a stock cat and rewelded it to a custom mid pipe i made.

Dann

Yes this was for me and it works very well!!

vrmmmpshhh wrote:The NA has what looks to be a temp sensor in the cat. What are people doing for aftermarket setups?

Leave it unplugged. That'll leave the light off on the dash and shouldn't affect performance. (On a '90 Eunos as least..)

Could maybe clean it the way you would a silencer, soak it in fuel, then light it and let it burn

Mr Sexy wrote:Could maybe clean it the way you would a silencer, soak it in fuel, then light it and let it burn

I'm pretty sure one of the things that causes cats to become clogged/collapsed is running too rich which causes the fuel to burn in the cat, and overheats it.


I can easily see soaking it in fuel and burning it to rather exagerrate the above.