The Official Blown Catalytic Converter Thread

[RoofRails]

Question about the rattle from exhaust at 1.1-1.2k rpm. Is that cat issues? Also silver speckles in exhaust tips? No real smell. Stage 1 IE for 7k miles 41.5k miles on a 2013 S4.
I’m going to be pissed if that’s happening just added IE downpipes would have done JHM test & catted dp if I thought I was losing them.

The silver dust is definitely a sign that they are starting to break up and a rattle can also be related if a piece of the matrix has come loose.

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[MSq5]

Replied.

For the group: stock cats are still in place. Taking it easy, mostly driving a third vehicle. A good local performance Indy shop is working up a proposal to do test pipes with Vibrant Ultra Quiet resos in downpipes with the remaining cat back kept stock. They do a lot of high horsepower street cars with test pipes. We have no testing here. Given my power increase over stock they think the Red Star catted shielded test pipes may not survive, but they have never actually had any experience with them. Just speculation based on melting the OEM and looking at tbe photos I took through the scope.

I'll see what they want to charge and their plan. Says he may have to cut the cats some to get them out and does not recommend gutting them. Says the sound would be bad, even with resos. The guy is really into high hp street cars - street/dragstrip, and knows how heat melts cats. He wants to go test pipes and resos. I can always fit downstream cats later if I don't like the smell. My last performance car was catless. I got used to the smell. With windows up and a/c on in recirc mode, didn't really cause a problem for passengers.

Update:

Shop says they can do it. They put it up on a lift, let me get under there with them. They showed me how they will proceed. Makes sense. Told me to get the parts coming. They recommended test pipes at my power level to reduce repeat melting. (We have no state inspection or testing) so I ordered:

Red Star Exhaust heat shielded test pipes, gaskets, 02 sensor extenders.

We decided to see how it sounds with the stock exhausts. They can add Vibrant Ultra Quiets if If I'm not happy. If its too stinky, they said there does appear to be room for downstrean cats in the OEM downpipes.

In the meanwhile, I now have low cat efficiency code on both cats, not just driver side. I've not scoped the passenger side. Doesn't matter, but I'm sure its melted too.

For those who have ordered from Red Star: How long between order and delivery? They claim 4-6 business days. Seems very optimistic unless they have a warehouse in USA.

[JayCar]

Update:

Shop says they can do it. They put it up on a lift, let me get under there with them. They showed me how they will proceed. Makes sense. Told me to get the parts coming. They recommended test pipes at my power level to reduce repeat melting. (We have no state inspection or testing) so I ordered:

Red Star Exhaust heat shielded test pipes, gaskets, 02 sensor extenders.

We decided to see how it sounds with the stock exhausts. They can add Vibrant Ultra Quiets if If I'm not happy. If its too stinky, they said there does appear to be room for downstrean cats in the OEM downpipes.

In the meanwhile, I now have low cat efficiency code on both cats, not just driver side. I've not scoped the passenger side. Doesn't matter, but I'm sure its melted too.

For those who have ordered from Red Star: How long between order and delivery? They claim 4-6 business days. Seems very optimistic unless they have a warehouse in USA.

Any updates on your exhaust setup?

[JayCar]

Just pulled these yesterday (engine is out for other reasons). Thoughts/opinions on these? They appear to be ok, but I'm not an expert in this area.

[MSq5]

Any updates on your exhaust setup?

Redstar Exhaust shipment arrived. The shielded test pipes are extremely well made. I'm on the road (in another vehicle) and will take the Q5 in to the exhaust shop that will be doing the work when I get back.

I have a simple question. It looks like the primary O2 sensor screws into the tail of the exhaust manifold (header) on each bank. Is that correct? Each test pipe has only one bung, presumably for the rear O2 sensor.

[MSq5]

Just pulled these yesterday (engine is out for other reasons). Thoughts/opinions on these? They appear to be ok, but I'm not an expert in this area.

There is some slight degraded matrix in a couple photos, but they look generally ok.

[RoofRails]

Redstar Exhaust shipment arrived. The shielded test pipes are extremely well made. I'm on the road (in another vehicle) and will take the Q5 in to the exhaust shop that will be doing the work when I get back.

I have a simple question. It looks like the primary O2 sensor screws into the tail of the exhaust manifold (header) on each bank. Is that correct? Each test pipe has only one bung, presumably for the rear O2 sensor.

You are correct. The test pipes are set up just like the cats with 1 bung for the rear O2.

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[mannes]

hello everybody,

I'm currently comparing various chip tuning options (MTM vs Turboperformance.de vs APR), and somehow I got the hint that the cats somehow like to go bust because of the higher temperatures.
So what's the story? should I expect them to break down if I chip tune my car? Under which circumstances does this happen, only if I drive hard or also by a casual driving style?

My car has currently about 131.000km on the clock

[MSq5]

hello everybody,

I'm currently comparing various chip tuning options (MTM vs Turboperformance.de vs APR), and somehow I got the hint that the cats somehow like to go bust because of the higher temperatures.
So what's the story? should I expect them to break down if I chip tune my car? Under which circumstances does this happen, only if I drive hard or also by a casual driving style?

My car has currently about 131.000km on the clock

What do you mean by "chip tune". There are piggy-back tunes that mostly lie to the ECU to force it to raise boost or alter sensor values to manipulate their signals. Then, there are real ECU tunes. They are programming file maps that are flashed directly to the ECU, replacing the OEM file. APR is among the latter. There are others here in the US, such as 034 and EPL, among others. For the most part we are using these flash tunes. They completely retune the ECU, altering boost, timing, fuel, under all different engine load, throttle position, rpm and even gear selection.

The problem with cat failures is believed to be multi-factorial. Mostly, it is related to the location of the cats being directly attached to the engine exhaust manifold/headers. Yes, its heat that usually kills them and aftermarket tunes do produce higher exhaust gas temperatures. Its a necessary byproduct of raising horsepower. The more power, especially if air-to-fuel ratio is not richened under high load.

Having said that, if you are worried about saving your cats, options are a bit limited if your government requires emission testing. A stage 1 tune is the safest aftermarket tune. It does not change supercharger speed in relation to crank speed. Stage 2 with a pulley ratio less than 3:1 is fairly safe. That is a smaller supercharger pulley alone, or a larger crank pulley alone in the range of 179mm to about 187-189mm or so.

Go higher and the risk increases proportionally. Ratios above 3:1 definitely require a larger air-to-water heat exchanger (intercoolers) to better cool the supercharger cores and the air going to the intake valves. Even stage 1 tunes benefit from better cooling, although not "necessary." Cooling is marginal even for the stock tune.

I mention cooling because higher boost above stock levels and the resultant increase in intake air temperature is associated with supercharger water intercooler leaks. When they leak, the water leaks into the cylinder head combustion chamber through the intake valves. That water vapor and the antifreeze and water pump lubricant end up as a part of the exhaust gas. It can be harmful to the matrix in the catalytic converters. This is a secondary or contributing cause of cat failure. It is typically evidenced by slow loss of coolant in the coolant reservoir and a whit-ish deposit on one or more spark plugs.

Executive summary: Higher heat and coolant loss = shorter cat life. As boost goes up heat goes up. Conservative tunes pose less risk, but no tune is 100% safe. Yes, conservative driving keeps exhaust gas temperatures lower and helps with cat life. Long full throttle runs can contribute to cat failure, especially with aggressive tunes.

A good relatively safe upgrade with a nuce power bump would be a "single pulley" stage 2 tune (179-187mm) crank pulley cimbined with a heat exchanger upgrade.

[mannes]

firstly thanks for the info!

it doesn't matter whether piggy-back or re-programmed ECUs. MTM offers both, which makes it quite appealing to me, since it means I can install it myself. it's a busy period for me right now, meaning that I don't quite have the time to go to a tuner to spend a whole day there. Turboperformance takes a different approach for tune-at-home. They will send you a device that connects to the car via OBDII, will gather various info, then you send the gathered information back to the tuner, and you'll get the new "tuned" mapping that you flash to your car using the same device. Also a nice approach for people with a busy schedule or living far away from the tuner's location.

I do want to get a performance increase, I also have the budget reserved for it since quite a while, but it's also important not to bust the cats. I'm waiting for a new born :) and I don't to end up pumping 2000€ in a pair of new catalytic converters and other parts instead of providing for the family. After all, it's the family station wagon / estate / Combi we're talking about. Yep, in Europe S4 came mostly in this shape, much like the current RS line.

I was looking anyway to stage 1 tuning alone, without any increase of the boost. which perhaps will come at some later time.

What would you consider an aggresive tune vs a conservative one? How would the torque curve look like in the lower RPM range vs in the higher, and where would you expect to have the max. torque? After analysing many torque curves, I would categorise APR as conservative, wheras MTM's 440PS (BHP) would be somehow more aggressive, since the torque curve goes up early very abruptly.

Currently I consider the following tuners: APR, MTM, SKN, and turboperformance[dot]de.

[mannes]

So let's talk numbers:

- APR stage 1 tuning torque curve: https://www.goapr.com/products/softw...0T-EA837-SIM84
BTW, how da' hell it costs just 600$ in US, whereas in Germany the same tuning costs 1600€???

- MTM 440BHP
presentation: https://www.mtm-online.de/en/configu...ning/S4B8A245Q
diagram: https://media.mtm-online.de/media/Ki...-b-333-440.pdf

- MTM 430BHP with M-Cantronic piggy-back
presentation: https://www.mtm-online.de/en/configu...ning/S4B8A245Q
diagram: https://media.mtm-online.de/media/Ki...-b-333-430.pdf

- Turboperformance torque curve. it's stage 2 (Stufe 2) that I'm after. apparently they offer a gearbox optimisation for this tune, but I drive a manual. good luck optimising me! even if it's in German, you should get the point...
https://www.turboperformance.de/chip...-tfsi-s4-333PS

annoyingly SKN don't offer a performance diagram. they said it's under data protection. haaa???
https://skn-tuning.de/shop/de/chiptu...333-ps-stufe-1
https://skn-tuning.de/shop/de/chiptu...333-ps-stufe-2

well lads, please welcome German prices for chip tuning...

[MSq5]

firstly thanks for the info!

it doesn't matter whether piggy-back or re-programmed ECUs. MTM offers both, which makes it quite appealing to me, since it means I can install it myself. it's a busy period for me right now, meaning that I don't quite have the time to go to a tuner to spend a whole day there. Turboperformance takes a different approach for tune-at-home. They will send you a device that connects to the car via OBDII, will gather various info, then you send the gathered information back to the tuner, and you'll get the new "tuned" mapping that you flash to your car using the same device. Also a nice approach for people with a busy schedule or living far away from the tuner's location.

I do want to get a performance increase, I also have the budget reserved for it since quite a while, but it's also important not to bust the cats. I'm waiting for a new born :) and I don't to end up pumping 2000€ in a pair of new catalytic converters and other parts instead of providing for the family. After all, it's the family station wagon / estate / Combi we're talking about. Yep, in Europe S4 came mostly in this shape, much like the current RS line.

I was looking anyway to stage 1 tuning alone, without any increase of the boost. which perhaps will come at some later time.

What would you consider an aggresive tune vs a conservative one? How would the torque curve look like in the lower RPM range vs in the higher, and where would you expect to have the max. torque? After analysing many torque curves, I would categorise APR as conservative, wheras MTM's 440PS (BHP) would be somehow more aggressive, since the torque curve goes up early very abruptly.

Currently I consider the following tuners: APR, MTM, SKN, and turboperformance[dot]de.

Stage 1 does increase boost under most conditions, holding the bypass valve closed longer. It also increases timing and fuel flow. In the US almost all ECU tunes (not APR) are flash-at-home via cloud servers and a laptop. Not familiar with the brands you mention.

[mannes]

Stage 1 does increase boost under most conditions, holding the bypass valve closed longer.

I'm well aware of that.
Pulley upgrade is something I want to avoid for the moment.

[MSq5]

I'm well aware of that.
Pulley upgrade is something I want to avoid for the moment.

You said "I was looking anyway to stage 1 tuning alone, without any increase of the boost. which perhaps will come at some later time."

That's what made me think you were saying Stage 1 tunes do not increase boost. Remapping alone can raise boost several psi without pulleys.

As it cosr, perhaps tbere are differences in the Eurospec ECUs and those in the US mandating a different tune. I don't know. Have you explored whether US based flash at home tuners like 034 or EPL have Euro versions. If so, physical location is not relevant.

[mannes]

the discussion seems to go a bit in a different direction.

to bring it back on track, what should I look for in a tuning that won't lead (at least that easily) to having broken cat converters? what would be a somehow safer torque curve?

because in the end, it seems that many catalytic converter failures are a direct result of a performance tuning.

[M1k3ee]

the discussion seems to go a bit in a different direction.

to bring it back on track, what should I look for in a tuning that won't lead (at least that easily) to having broken cat converters? what would be a somehow safer torque curve?

because in the end, it seems that many catalytic converter failures are a direct result of a performance tuning.

If you live in Germany (autobahn, no speed limit), I wouldn't tune the car if you are afraid of the catalytic converters breaking. Stock exhaust gas temperatures are already borderline safe for the catalytic converters if you drive 100 - 140 mph (~180 kmh - 240 kmh) continuously. Furthermore, the catalytic converters are known to fail on stock power levels on the B8 S4, and the failure rate will increase when you tune them. The only possible (custom) ECU tuning that I can think of which will not increase the failure rate, is if you leave the boost as is and only add some ignition timing as this will likely decrease the EGT and add some hp (although not much and not worth it imo compared to the cost).

If you decide to tune your car anyway, I would opt for 034 Motorsport or Integrated Engineering for the B8 S4 (both have flash at home capabilities, have higher quality files for your car and are cheaper than the tuning firms you mentioned).

[MSq5]

the discussion seems to go a bit in a different direction.

to bring it back on track, what should I look for in a tuning that won't lead (at least that easily) to having broken cat converters? what would be a somehow safer torque curve?

because in the end, it seems that many catalytic converter failures are a direct result of a performance tuning.

Not sure why the emphasis on torque curve if you stay at stage 1. This is a supercharger engine, not a turbo. Torque is immediate, even on stock tune. However, all stage 1 tunes will mostly raise power at the top end under full throttle, above 4,000 rpm. You may not notice much change in torque at lower rpm or part throttle. That's the nature of how the engine makes power on stock pulley tunes.

Marketing hype on power should be taken with a grain of salt. All stage 1 tunes, at least on US spec cars, will be very close in actual performance. If you want to go the flash-at-home route, 034 or IE produce maybe 5 more hp on top end over EPL, while EPL is a bit more conservative with timing and perhaps a bit richer in AFR to stay safer. But, at that power level they are all about the same.

Expect power to be about 420-430 crank horsepower SAE gross for any of these Stage 1 tunes and regardless of whether the engine was OEM tuned for 272 or 354 hp.

The torque curve does get more aggressive with Stage 2 single and dual pulley tunes, very noticeably so, because the supercharger turns faster and makes more available boost everywhere. This is apparent (and welcome for many of us) even in daily driving, as the torque comes in earlier and greater at lower rpm and lower throttle position.

I have the 272 hp Q5 (US spec) 3.0T which was purposefully detuned by Audi as not to pull sales from the SQ5 which has an otherwise identical engine, just tuned to 354 hp. So, the jump from 272 to 430 or so on stage 1 EPL was far more dramatic than if I started with 354. Stage 1 equaluzes the power at about 430.

Now, Stage 2 single pulley and double pulley tunes do not increase absolute power very much - maybe 40-50 hp. While not insignificant, their real benefit is the huge bump up in low and midrange torque. Everywhere, not just up top as with Stage 1 tunes.

If your goal is a reasonable bump up in power while staying as safe as possible, consider EPL stage 1, if they have an Euro box code tune. I have progressed from stock to Chipwerke Pro (piggy back when in warranty) to EPL stage 1, then EPL stage 2 to now EPL stage 2 dual pulley. I like the slightly more conservative tuning approach and its superb customer support.

Shorter answer: Get any reputable flash-at-home stage 1 tune. They are all within 95% of each other. Seek a more conservative one if cat life is paramount. That would be EPL in the US.

Since you have a manual transmission, you might want to try tbe Chipwerke Pro Stage 1 piggy back. It works well with manual transmission cars, a bit less so with dual clutch or automatic transmission cars. Its much less expensive. It does not change timing or fuel, but merely alters the manifold pressure sensors signal to permit tbe bypass valve to stay closed longer. I actually liked it. Power level is about the same as true stage 2 tunes. My ZF8 automatic transmission did not like it. The transmission's computer still thought the engine was stock, so part throttle upshifts were too quick and abrupt. With a manual that would not matter. It would be safest, as it does not alter any of the ECU's safety features and does not affect anything other than bypass valve operation. You just insert it to the manifold pressure sensor plugs. Takes 5 minutes and is fully reversible.
I hope this was of some use.

[Ahsan421]

Hey guys,

So I have a 2015 b8.5 S4 at 50k miles. I recently got a code P0420. I was wondering if you were able to get your cats replaced under warranty. I'm stage 1. I do have 1185 magna flow & tips on the exhaust. Do you have any recommendations on how to get the dealer to cover it under the 80k/ 8 Year warranty. Does anyone have any experience with this ?

Thank you

[AerotusX]

Hey guys,

So I have a 2015 b8.5 S4 at 50k miles. I recently got a code P0420. I was wondering if you were able to get your cats replaced under warranty. I'm stage 1. I do have 1185 magna flow & tips on the exhaust. Do you have any recommendations on how to get the dealer to cover it under the 80k/ 8 Year warranty. Does anyone have any experience with this ?

Thank you

My case exactly. My cat failed at around 68K this past April. I called the dealer and mentioned the federal warranty. They checked and said it's covered at no cost. I have APR Stage II, flashed back to stock. I also have the 11385, resonator delete, and 4" tips. No issue. Make sure you mention the federal warranty upfront, otherwise, they may try to charge you.

[Ahsan421]

My case exactly. My cat failed at around 68K this past April. I called the dealer and mentioned the federal warranty. They checked and said it's covered at no cost. I have APR Stage II, flashed back to stock. I also have the 11385, resonator delete, and 4" tips. No issue. Make sure you mention the federal warranty upfront, otherwise, they may try to charge you.

Did you have to pay diagnostic fee? They are charging me to see first.

Thank you


Sent from my iPhone using Tapatalk

[AerotusX]

I didn't need to pay anything, No diagnostic fee.

[850tgul]

I didn't need to pay anything, No diagnostic fee.

How did you know, for sure, that it was a bad car without having a shop look at it first?

[850tgul]

I didn't need to pay anything, No diagnostic fee.

How did you know, for sure, that it was a bad cat without having a shop look at it first?

[MSq5]

How did you know, for sure, that it was a bad cat without having a shop look at it first?

I don't know how he knew. But, if curious, you can stress test the cats with a diagnostic test in RossTech VCDS. Also, You usually first get a soft code of cat low efficiency for bank 1 or bank 2 or both. This will eventually throw a hard code and a check engine light.

If in doubt, you can scope each cat in place with an inexpensive bore/inspection cable mounted camera. They are only about $30 or so on Amazon and connect to your laptop, tablet or some cell phones. You remove the primary (front) O2 sensor and drop it in the hole and look at the front of the cat's substrate or matrix for cracks or melting. That sensor is actually in the tail of the exhaust manifold.

[AerotusX]

In my case while driving one day, I heard a loud pop noise. Then my car suddenly sound like a loud lawn mower. I went under the car and could see one of the cats have a crack at the flange.

I just called the dealer and told them that one of the cats was cracked. They told me to bring it in and they will look at it to make sure. They did not mention any diagnostic fee. I mentioned to them about the federal warranty ahead of time.

[Audibellybutton]

Just here to tell a story about how I gutted my failing cats on my 3.0t Audi A7

I want to give the disclaimer that this is not advice, could even be a bad idea. It was a risky move on my part but i had no fucks to give at the moment, and it worked. worked well actually.



So anyways I was dual pulley and started to get codes, cat efficiency and what not.

I had a fairly straight through exhaust, suitcase and muffler deleted

I was reading old posts on the forums and I saw a few people make a joke about gutting the cats using a plumbing snake, or by putting water into the cat lol i think it was ntsantos or something, either way it was obviously a joke. but seemed plausible. I have had gutted cats on my other boosted car before and had left over 02 spacers so i thought... WHY TF NOT

Anyways, cut to the chase, I first opened up and pulled the rear o2 sensor and put water from a water bottle in there, just a little bit then I capped it and started it. Well, nothing happened.

Then i removed the front o2 sensor and did the same thing. When I revved the car I saw pieces of cat fly out, so I took the car for a couple pulls with my brother following me to make sure it was working. Sure enough, the exhaust blew out a ton of cat material, big chunks, small chunks, dust, all of it. After that, with the spacers on I had no codes and i noticed an increase in performance, increase in fuel smell (catless) but i still wasnt 100% confident with my decision, what if there was still chunks of cat in there that I didnt know about? so I bought a mechanic camera off of amazon, (borescope) and I inserted it into the front o2 hole on both sides to inspect, there was no more cat material at all, so the trick was successful

now in hindsight, would I do it again if i had a failing 3.0t cats? Yes.
Would I advise other people to try this? No, I dont want to be responsible for any damage.

Would I do this on my c7 4.0t cats? No, Ive heard these cats are much more robust, plus i feel like theres much more on the line and the turbo engine might work differently, either way I dont think i would gut cats in this way, on this car, but I would definitely still run gutted cats on this car if the cat ever started failing. Easy to pass smog with gutted cats.

Anyways hope you guys enjoy this story. Do what you want with this info, but I DID NOT TELL YOU TO GUT YOUR CATS WITH WATER
just telling you my experience. thats all

good luck to everyone

[RoofRails]

Just here to tell a story about how I gutted my failing cats on my 3.0t Audi A7

I want to give the disclaimer that this is not advice, could even be a bad idea. It was a risky move on my part but i had no fucks to give at the moment, and it worked. worked well actually.



So anyways I was dual pulley and started to get codes, cat efficiency and what not.

I had a fairly straight through exhaust, suitcase and muffler deleted

I was reading old posts on the forums and I saw a few people make a joke about gutting the cats using a plumbing snake, or by putting water into the cat lol i think it was ntsantos or something, either way it was obviously a joke. but seemed plausible. I have had gutted cats on my other boosted car before and had left over 02 spacers so i thought... WHY TF NOT

Anyways, cut to the chase, I first opened up and pulled the rear o2 sensor and put water from a water bottle in there, just a little bit then I capped it and started it. Well, nothing happened.

Then i removed the front o2 sensor and did the same thing. When I revved the car I saw pieces of cat fly out, so I took the car for a couple pulls with my brother following me to make sure it was working. Sure enough, the exhaust blew out a ton of cat material, big chunks, small chunks, dust, all of it. After that, with the spacers on I had no codes and i noticed an increase in performance, increase in fuel smell (catless) but i still wasnt 100% confident with my decision, what if there was still chunks of cat in there that I didnt know about? so I bought a mechanic camera off of amazon, (borescope) and I inserted it into the front o2 hole on both sides to inspect, there was no more cat material at all, so the trick was successful

now in hindsight, would I do it again if i had a failing 3.0t cats? Yes.
Would I advise other people to try this? No, I dont want to be responsible for any damage.

Would I do this on my c7 4.0t cats? No, Ive heard these cats are much more robust, plus i feel like theres much more on the line and the turbo engine might work differently, either way I dont think i would gut cats in this way, on this car, but I would definitely still run gutted cats on this car if the cat ever started failing. Easy to pass smog with gutted cats.

Anyways hope you guys enjoy this story. Do what you want with this info, but I DID NOT TELL YOU TO GUT YOUR CATS WITH WATER
just telling you my experience. thats all

good luck to everyone

If I'm thinking about this correctly the water creates a hydraulic blockage that uses your exhaust back pressure to push / blow the cat material out or is it somehow breaking the ceramic catalyst material down ? If Its my initial thought of using back pressure then yes what you did was extremely risky and you may if nothing else have damaged the exhaust valve seals with the back pressure.

If you cant be without the vehicle for a while have a back up plan in place for a flange weld failure. Its become the excepted practice now to reinforce the flange welds when using gutted cats to avoid having to remove them for a failed weld.

[Audibellybutton]

If I'm thinking about this correctly the water creates a hydraulic blockage that uses your exhaust back pressure to push / blow the cat material out or is it somehow breaking the ceramic catalyst material down ? If Its my initial thought of using back pressure then yes what you did was extremely risky and you may if nothing else have damaged the exhaust valve seals with the back pressure.

If you cant be without the vehicle for a while have a back up plan in place for a flange weld failure. Its become the excepted practice now to reinforce the flange welds when using gutted cats to avoid having to remove them for a failed weld.

My cat was failing due to clogging/possibly melting from heat due to pulley upgrade, it was really choking it up. My fears stemmed from horror stories of cats melting and clogging completely and seizing the engine. I didn’t have any flange issues in my case

Not defending the method at all, again it’s not advice but my logic was that since the engine and exhaust want to blow everything outward, a little assistance would dislodge the remaining cat material. I’m not sure how or why the water worked, or why someone suggested it but it definitely did in my case lol. It’s crazy but it gave me a lot of relief

I don’t have the car anymore, but after doing this I ended up going higher PR and adding meth and e85 and tb upgrades and was getting healthy logs out of the motor since then. The car was running much better with the gutted cat

But yeah results could have been different and caused damage that was a gamble I took that most ppl wouldn’t take

[RoofRails]

My cat was failing due to clogging/possibly melting from heat due to pulley upgrade, it was really choking it up. My fears stemmed from horror stories of cats melting and clogging completely and seizing the engine. I didn’t have any flange issues in my case

Not defending the method at all, again it’s not advice but my logic was that since the engine and exhaust want to blow everything outward, a little assistance would dislodge the remaining cat material. I’m not sure how or why the water worked, or why someone suggested it but it definitely did in my case lol. It’s crazy but it gave me a lot of relief

I don’t have the car anymore, but after doing this I ended up going higher PR and adding meth and e85 and tb upgrades and was getting healthy logs out of the motor since then. The car was running much better with the gutted cat

But yeah results could have been different and caused damage that was a gamble I took that most ppl wouldn’t take

I didn't realize this was written about a car you use to have. Well it sounds like luck was on your side.

Sent from my SHT-W09 using Audizine mobile app

[Audibellybutton]

I didn't realize this was written about a car you use to have. Well it sounds like luck was on your side.

Sent from my SHT-W09 using Audizine mobile app

Yeah car is gone now but to elaborate I did some research. Apparently the cat material is magnesium and it reacts with the water and heat. In my case it blew the cat pieces directly out of my exhaust that was pretty free flowing. It seems the potential for damage could come if the cat did not blow the pieces outward, but the back pressure helps with that. If your exhaust was not free flowing the pieces could get stuck in a muffler or resonator or something. So I would be cautious of that.

[tpivette89]

Just scoped the drivers side cat. Does this look good?

Audi cat1.jpgAudi cat2.jpg

[Fresh.S4]

yup. no cracks or elevated areas. if you want to go an extra mile, scope the other end.

[MSq5]

Looks ok to me.

If the cat is failing the matrix will start to melt and fuse together, blocking flow. Here's what my failed driver side cat looked like through a acope.

[ubernoob]

Anyone selling stock/oem cats in good condition for my B8.5 Q5 3.0T?

Thanks!

[egebhardt]

You could go to the Wanted section. Maybe see some for sale in the Classifieds.
https://www.audizine.com/forum/forum...isc-Automotive

Also, "good" condition is a subjective word. One guy might say it's good and they fail in 1,000 miles.
Instead of spending your money twice, new might be the least-risky option.

[egebhardt]

After reading 90% of this thread, I've determined the following:
1 - the cats often fail because the engine is getting more fuel (per a tune) and/or more boost (via 1 or 2 pulleys). The extra engine heat burns the magnesium honeycomb material and the cats start to crumble and clog that pipe or eventually blow out the back with a P0420 code.
2 - one reasonable fix is to buy cat-less downpipes (the exhaust pipe section just after the headers) and put a Vibrant 1141 muffler in the mid-pipe (section of exhaust after the downpipe). The Vibrant 1141 is out of stock as of today from that Chicago company.

I thought this was a good diagram so everyone could understand what part is what. We can all be on the same page this way.

Full-Exhaust-Diagram.jpg

[MSq5]

After reading 90% of this thread, I've determined the following:
1 - the cats often fail because the engine is getting more fuel (per a tune) and/or more boost (via 1 or 2 pulleys). The extra engine heat burns the magnesium honeycomb material and the cats start to crumble and clog that pipe or eventually blow out the back with a P0420 code.
2 - one reasonable fix is to buy cat-less downpipes (the exhaust pipe section just after the headers) and put a Vibrant 1141 muffler in the mid-pipe (section of exhaust after the downpipe). The Vibrant 1141 is out of stock as of today from that Chicago company.

I thought this was a good diagram so everyone could understand what part of the exhaust is what. It's safe to assume some people don't know.

Full-Exhaust-Diagram.jpg

My fix was go with catless downpipes followed by small bottle cats, then Vibrant Ultra Quiet resos in place of the OEM ones. That is Vibrant 1141. Remainder is OEM exhaust. The bottle cats are ceramic core, high flow, and just to kill the smell. They are not emission compliant. Note: the Flowmaster cats in the photo are steel core. They failed. I replaced them with ceramic core Magnaflow bottle cats, the same size. Flow just as well and are better constructed.

[Fresh.S4]

IMG_20241130_122422.jpg

I went with catless downpipes to magnaflow cats to vibrant 17930. I bought the UQs as well but when doing research, i felt it was just as important to have longer resonators so sound has more to get absorbed. The UQs also are a lil trickier to mount under an s4 because of space.

[MSq5]

IMG_20241130_122422.jpg

I went with catless downpipes to magnaflow cats to vibrant 17930. I bought the UQs as well but when doing research, i felt it was just as important to have longer resonators so sound has more to get absorbed. The UQs also are a lil trickier to mount under an s4 because of space.

Well done! Yes, the S4 is a bit more cramped than my Q5. I went with the Ultra Quiet resos for rasp control because they had worked well in several other catless cars I have owned. They are oval shaped and had to be turned a little sideways to fit. Maybe 17930 might be better. Dunno. All I can say is that the Ultra Quiet resos and the magnaflow bottle cats really work to kill both drone and rasp.

[Twi7ch]

My fix was go with catless downpipes followed by small bottle cats, then Vibrant Ultra Quiet resos in place of the OEM ones. That is Vibrant 1141. Remainder is OEM exhaust. The bottle cats are ceramic core, high flow, and just to kill the smell. They are not emission compliant. Note: the Flowmaster cats in the photo are steel core. They failed. I replaced them with ceramic core Magnaflow bottle cats, the same size. Flow just as well and are better constructed.

What symptoms did you get when your flowmaster cats failed? I currently have Flowmaster 200 cells near the transmission and I just did a long road trip (1500 miles) and I noticed my exhaust note has changed. I'm a bit concerned as I have 1500 miles to go to get back home...

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