rotaryPilot

Hi all,

I have the impression that my cat is broken. Well this impression came from the event of hearing metallic sounds in some specific revs. In addition, a friend of mine which has also broken cat has gone to the dealer and they have checked that his cat is broken and they have ordered a new one. Yesterday I met my friend who has not replaced yet his cat and I certified that the metallic sound I can hear at 1500revs sounds exactly the same as my friend’s car at 1500revs. As a result I suppose that my cat is broken too. I have scheduled a visit to my dealer in order to check it too.

However, my car now that I believe that has broken cat performs better than before that I was NOT able to hear any metallic sounds.

Is this possible?

I mean how is it possible that you may have a broken cat and the car to perform better than when you were with a good cat? If this is the case I believe that the flow around the cat may have been improved which sounds very awkward and in the real case the flow of a broken cat is much worse than the flow of a good cat.

So to complete my description, my car revs very fast till the rev limiter and it feels very powerful having a very good throttle response. It can accelerate very good and satisfactory at any gear.


Any thoughts around this issue?

MrCairo

Anything that reduces the back-pressure of exhaust from your car will improve performance. So, a broken cat that improves the flow will definitely improve performance. I remember a time when friends would remove their cat for this very reason. Of course, its not legal to run a car without a cat these days (or even a broken one) so its good that you are getting it fixed.

rotaryPilot

^ ok, this sounds reasonable BUT if the cat is broken and as a result the back-pressure is reduced ( and you have better performance ) what happens with the pieces of the broken cat??? I guess that a broken piece can get into the flow way and increase a lot your back-pressure and actually reduce your performance. And this is logical where do they go the broken pieces? I think it is impossible to get out from the exhaust muffler.

nate340

a month ago i had a CEL, went to the dealer they said it was a bad cat. took 2 weeks for them to replace it. during the 2 weeks i had my car i noticed worse and worse preformance and gas consumption.

4me2

car without Catalysts,,,,,,,stink.

alnielsen

iTrader: (4)

I have had 4 oem cats go bad on my car so far. They all caused a restriction rather than opening up the exhaust.

rotaryPilot

So as I see from your posts guys it is not possible to have a bad cat and notice a better performance in your car.

As a result either I am the only one the experiences this kind of phenomenon or the metallic sound I am able to hear it is not any piece attached from a bad cat but some other issue with my exhaust or heat shield.

kersh4w

iTrader: (3)

no.

if you want the best performance, just take your entire exhaust off. if your cat is broken in some way that improves air flow out of the engine, your car will have better performance. this train of thought is why ricers ride around with 6" exhausts. although, for a NA engine, you need some back pressure, otherwise you get a loss of hp. for a turbo car however, the bigger the better. the less resistance means more hp.

an rx8 forums for greek owners? rofl, last time i was there gas was crazy expensive. i love greece though, some day i'll build a house in the mountains overlooking the sea. the mountains smell so nice, all the herbs giving the whole place a very aromatic smell. i miss greece.

8 Maniac

iTrader: (1)

Hopefully someone better informed can elaborate on this, but I thought back pressure wasnt an issue with the rotary?

zoom44

no air out= no air in
no air in = no power
more air out = more power
clogged cat=no air out
clogged cat whose catalyst has broken into smaller pieces and is no longer stopping the air from going out=better performance

in an NA or FI rotary 0 back pressure= best power

KeithL

I think there's a thread in the Performance or DIY section about removing part of the catalyst from the stock converter. Apparently there's two sections of catalyst, and removing one of them maintains the functionality of the cat. whilst allowing higher flow....

stuartm

Why does a NA engine NEED back pressure?

rotaryPilot

Very Informative and I guess that rotary needs no back pressure because has no overlap.

rotaryPilot

Yes the gas is kind of expensive hear. The unleaded 95 costs almost 0.72 dollars and the premium unleaded 100 costs almost 0.91 dollars. However 100 octans is a good quality.

I guess if you come again in Greece you can visit me so you can get an idea for your future house. Because my house is built on a mountain that has a view to the sea.

arghx7

So you're hearing a funny noise and you think that you have a bad cat, even though you are not throwing a code? I find that unlikely.

kersh4w

iTrader: (3)

http://www.warnertechnology.com/Cars/backpressure.shtml

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my father has a cabin up in the mountains in northern Peloponnese over looking the sea. he lives in Patras though. i guess i didnt mention im half greek. how is greece holding up right now btw? i've read a half dozen reports of all of southern Peloponnese being up in flames. and even the outskirts of Athens are in danger. i've seen a few pictures on reuters that look like they came from a post apocalyptic nuclear winter. stay safe.

stuartm

You are talking about gas velocity not back pressure. Removing the cat reduces back pressure & increases gas velocity.

alnielsen

iTrader: (4)

That DIY is a little erroneous. There are 2 parts to the cat. The first part is suppose to warm up quick to reduce exhaust gasses when the car is still cold. The second part it the part that does the bulk of the work. The DIY tells you how to break up and remove the second part.

Fanman

If you hollow out your catalytic you would get performance (not to mention check engine light, terrible smell, and louder), but I could not imagine a scenario where you would just blow all of the cat material through your exhaust. A much more likely scenario is that it gets stuck in your exhaust system & clogs up your car causing you to lose hp & eventually get engine failure.

nycgps

iTrader: (1)

I had a broken CAT once, it clogged up my 8 so much that I can barely reach 4K RPM.

After a few days I think everything got burnt off, the exhaust smells horrible, but performance is back, along with a CEL.

Replaced the CAT, Running for 20+K miles, no issues.

I wouldnt run around without a cat, cuz its really bad for the earth.

rotaryPilot

I went to the dealer and checked my exhaust. My cat was ok and the metallic sound was a metallic cover which was loosen a little bit before and above muffler !!!