2019 S4 DP, high flow v. Catless

[kakahoms]

Hi, I’m sure this has been a post in the past but with options being limited (sold out or discontinued) I was wondering what you guys have done for your downpipe? And why you went high flow v. Catless? I have the AWE Tuning switchpath and the IE intake already. also, I’ve read that catless may require more maintenance in the future?? I’m rather new to Audi’s and car mods so any input is appreciated!

[SHCKR]

Hi, I’m sure this has been a post in the past but with options being limited (sold out or discontinued) I was wondering what you guys have done for your downpipe? And why you went high flow v. Catless? I have the AWE Tuning switchpath and the IE intake already. also, I’ve read that catless may require more maintenance in the future?? I’m rather new to Audi’s and car mods so any input is appreciated!

Catless will result in louder exhaust tone, less restricted airflow, and a fairly unpleasant smell out of the exhaust, all at a decent price. High flow catted will be slightly less louder, somewhat restricted, no smell, and about triple the price.

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[JacobR]

Catless is 100% illegal, while a high flow still retains some sort of catalyst which may or may not pass emissions depending on it's quality.

If you're tuned on a stock turbo, there are a number of posts indicating no gain with any downpipe.

[jdel]

Catless is 100% illegal, while a high flow still retains some sort of catalyst which may or may not pass emissions depending on it's quality.

If you're tuned on a stock turbo, there are a number of posts indicating no gain with any downpipe.

Catless is not "100% illegal". Pay attention to your local state laws to determine if you can go catless without any issues.

[Jetta03]

Catless is illegal everywhere. Whether it is actually enforced or checked is the real question.
If you are going to bother with a downpipe mod at all, go catless. Otherwise it really isn't good value per horsepower.

[leozip]

if you are in fl, you can run Catless with zero problems. and yes the smell comes with it. but agree with above, go catless or don't bother at all.

[JacobR]

Catless is not "100% illegal". Pay attention to your local state laws to determine if you can go catless without any issues.

Nope. Federal emissions laws are in effect for all states, with the exception of California which can only go more strict in it's emission laws.

States all have different emission inspection requirements, so that's why people think it may be legal to go catless.

if you are in fl, you can run Catless with zero problems. and yes the smell comes with it. but agree with above, go catless or don't bother at all.

It's still illegal in FL: http://www.leg.state.fl.us/Statutes/...0316.2935.html

Whether anyone checks regularly is another story since FL stopped smog testing in 2000.


Emissions violations aside, if you're tuned on a stock turbo, any downpipe has proven to have no or extremely minimal performance gains.

[brilliant_black]

I had catless on for a week. My friends could smell me 4 cars behind that's how bad it was. If you want to run catless then you have to go e85 to make it bearable. It will stink way too much with regular gas.

I have a high flow cat now, and the car only slightly smells under hard acceleration.
I wish someone would make cat pipes to relocate them downstream instead.

The biggest restriction on sound is the cat being right behind the turbo. Catless sounded way more aggressive, but highflow cat still is a huge difference from stock.
I feel if we had a test pipe behind the turbo, then relocated cats further downstream, then that would be beneficial for sound and performance.

[INS4NE_B9]

If you are running the stock turbo, a downpipe will only net you more sound. Power gains aren't there until you outflow the stock cat, which the stock turbo is not capable of doing.

[Jadar]

If you are running the stock turbo, a downpipe will only net you more sound. Power gains aren't there until you outflow the stock cat, which the stock turbo is not capable of doing.

Can anyone explain in detail as to why this is on this platform? I’ve had 5 turbo cars from BMW’s to Ford Fiesta st to s3, they all net huge gains when going catless or 200cel and tune. I’ve seen this numerous times on the b9 s4/5 that a down pipe doesn’t do anything, why is that?


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[SHCKR]

Can anyone explain in detail as to why this is on this platform? I’ve had 5 turbo cars from BMW’s to Ford Fiesta st to s3, they all net huge gains when going catless or 200cel and tune. I’ve seen this numerous times on the b9 s4/5 that a down pipe doesn’t do anything, why is that?


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The factory is not that restricting, that's all there is to it.

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[Jadar]

The factory is not that restricting, that's all there is to it.

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I see. Thanks.


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[brilliant_black]

The factory is not that restricting, that's all there is to it.

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I don’t believe that to be honest. My 0-60 went down to 4.1 vs 4.3 when I put on the high flow cat on the stock tune.

Besides that these cars exhaust sound is incredibly weak without a high flow or catless pipe.


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[SHCKR]

I don’t believe that to be honest. My 0-60 went down to 4.1 vs 4.3 when I put on the high flow cat on the stock tune.

Besides that these cars exhaust sound is incredibly weak without a high flow or catless pipe.


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I'm not gonna lie, I love my catless sound!

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[JacobR]

I don’t believe that to be honest. My 0-60 went down to 4.1 vs 4.3 when I put on the high flow cat on the stock tune.

On stock software, think of it this way:
When you changed the downpipe, you changed the hardware model the factory software was created with.
This allows the turbo to end up spinning a little faster than software model intended, and you've gained some pressure/power.

Now with a tune, the turbo is being pushed harder and really has no more room. The stock pipe flows well enough for all the stock turbo can do.

This is why a downpipe makes no difference on a tune.

[Jadar]

On stock software, think of it this way:
When you changed the downpipe, you changed the hardware model the factory software was created with.
This allows the turbo to end up spinning a little faster than software model intended, and you've gained some pressure/power.

Now with a tune, the turbo is being pushed harder and really has no more room. The stock pipe flows well enough for all the stock turbo can do.

This is why a downpipe makes no difference on a tune.

Thanks that was a great explanation.


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[RogosMcGee]

On stock software, think of it this way:
When you changed the downpipe, you changed the hardware model the factory software was created with.
This allows the turbo to end up spinning a little faster than software model intended, and you've gained some pressure/power.

Now with a tune, the turbo is being pushed harder and really has no more room. The stock pipe flows well enough for all the stock turbo can do.

This is why a downpipe makes no difference on a tune.

I realize I’m resurrecting an old thread but I can’t be the first one reading through this as they research downpipes for the platform.

I don’t get the logic of this post. By the same token, you could argue that the downpipe allows the tune to take advantage of the increased turbo outflow and so you get a bump to performance.

Both 034 and IE insist you have to have a downpipe before they’ll take you to stage 2. The guys at 034 seem to actively dislike seeing owners swap the stock pipe (especially to go catless) for emissions reasons so if they’re insisting you need to swap before they’ll bring you to stage 2 there has to be a reason, right?

[oesman]

As I understand it 034 says there is more power to be had from a downpipe and it is also for catalyst protection. Here are some recent posts:

https://www.audizine.com/forum/showt...1#post14771160

Our Stage 2 file requires a downpipe as we found gains can be had with the increased flow from a downpipe.

https://www.audizine.com/forum/showt...1#post14771800

By running Stage 2 on a factory catalyst with our software, you are ultimately putting your cat at risk.

[FromS60toB61.8t]

I realize I’m resurrecting an old thread but I can’t be the first one reading through this as they research downpipes for the platform.

I don’t get the logic of this post. By the same token, you could argue that the downpipe allows the tune to take advantage of the increased turbo outflow and so you get a bump to performance.

Both 034 and IE insist you have to have a downpipe before they’ll take you to stage 2. The guys at 034 seem to actively dislike seeing owners swap the stock pipe (especially to go catless) for emissions reasons so if they’re insisting you need to swap before they’ll bring you to stage 2 there has to be a reason, right?

If you ran the stage 2 tune on a stock downpipe, you'd probably eventually burn out the internals over time.
From everything I've seen, you gain like 2-3 hp, but 20-30 ftlbs of torque between downpipe and no downpipe. I think it's more of preserving the stock cat vs possibly burning out the cells so they just cover themselves by requiring a downpipe on the stage 2.

[oesman]

From everything I've seen, you gain like 2-3 hp, but 20-30 ftlbs of torque between downpipe and no downpipe.

One thing to consider horsepower wise is that torque is the measured power and horsepower is derived mathematically as the amount of work being done. So if you added 20 to 30lb-ft of torque at say even as low as 1,000 rpm it would be at least 3.8 to 5.7hp, but the higher RPM the more horsepower you make. So if the torques are being added at say 4,000 RPM then you're talking 15.2 to 22.8hp. The math is just TQ x RPM / 5252, it's why all dyno charts intersect at 5,252 RPM, and why fake dyno charts are sometimes funny to look at.

So if you're making the torque before or after the peak powerband that gives you the highest overall horsepower number, it may mean the peak horsepower number only goes up a few horsepower. However, you may be adding well above 2-3hp off-peak and still making noticeable gains in the work being done (i.e. accelerating your vehicle forward). If the RPM range with the gains falls within your power band when accelerating of course (1,000 RPM would be much less useful than 4,000 rpm).

[RogosMcGee]

"By running Stage 2 on a factory catalyst with our software, you are ultimately putting your cat at risk."

I just ran this scenario by my buddy and he was like "I don't see what the problem is: go stage 2 and get a catless downpipe for free" lol. But there's some truth to what he's saying, right? If 034 and IE are mainly insisting on putting in an aftermarket downpipe to avoid people complaining that their stock cat was fried over time, why not just go stage 2 on the stock cat and let what happens happen, 10,000 miles later, congrats, you have a catless downpipe in an OEM housing -- I know 034's tune blanks the CEL anyway. I'm sort of joking not joking on this. I've been investigating RedStar downpipes which seem by every indication like great products but they're also expensive as hell for what seems like negligible gains.

[oesman]

The stock pipe is expensive, will be pricey if you want to sell the car as an on-road vehicle to a non-enthusiast. The cat is like $4k new. When it melts it won't become a free catless downpipe. It will be some combination of clogged and broken chunks of catalyst core bouncing around after your turbo. Also 034's tune only removes the CEL it does NOT bypass the readiness state for any sort of emissions testing.

[RogosMcGee]

The stock pipe is expensive, will be pricey if you want to sell the car as an on-road vehicle to a non-enthusiast. The cat is like $4k new. When it melts it won't become a free catless downpipe. It will be some combination of clogged and broken chunks of catalyst core bouncing around after your turbo. Also 034's tune only removes the CEL it does NOT bypass the readiness state for any sort of emissions testing.

*crosses crazy idea off list*

[S4UCE]

*crosses crazy idea off list*

Piggies were a pretty common mod for the B5 S4 before cheap knockoff downpipes were widely available. Remove downpipe, use a drill and wire wheel to break up and clear out the pre-cat, replace downpipe. Free horsepower!

[oesman]

Piggies were a pretty common mod for the B5 S4 before cheap knockoff downpipes were widely available. Remove downpipe, use a drill and wire wheel to break up and clear out the pre-cat, replace downpipe. Free horsepower!

Yep and it's still practice people do where they get visual parts inspections (i.e. I know someone in Switzerland who does this). You can definitely knock the core out of the down pipe, just don't recommend letting it happen "naturally" or really wasting the $4k part :-) especially if you go stock to sell.

[FromS60toB61.8t]

Piggies were a pretty common mod for the B5 S4 before cheap knockoff downpipes were widely available. Remove downpipe, use a drill and wire wheel to break up and clear out the pre-cat, replace downpipe. Free horsepower!

The thing is, a CTS catless downpipe cost $470, while you can sell the stock cat for $700-800. So if you were to already be taking the cat out to gut it, to me, it would only make sense to swap it out with a catless pipe and profit off of the stock cat if going that route.

Unless as mentioned above, you're worried about visual emissions inspections that is.

[RogosMcGee]

The thing is, a CTS catless downpipe cost $470, while you can sell the stock cat for $700-800. So if you were to already be taking the cat out to gut it, to me, it would only make sense to swap it out with a catless pipe and profit off of the stock cat if going that route.

Unless as mentioned above, you're worried about visual emissions inspections that is.

One of the reasons I'm considering the RedStar (https://redstarexhaustusa.com/audi-b9-s4-s5-downpipe) is because they actually make a B9 downpipe that is US emissions compliant (400 cpsi), although you sure pay for it. I'm thinking down the road about resale when the B10 platform comes out and I feel like that might make it a selling point, even if I end up selling the car to the community.

[SHCKR]

One of the reasons I'm considering the RedStar (https://redstarexhaustusa.com/audi-b9-s4-s5-downpipe) is because they actually make a B9 downpipe that is US emissions compliant (400 cpsi), although you sure pay for it. I'm thinking down the road about resale when the B10 platform comes out and I feel like that might make it a selling point, even if I end up selling the car to the community.

Redstar is heavily discussed in the DP thread on this forum, you might wanna check that out (search)

[oesman]

Also the whole russian thing

[Kedawerx]

Which thread is The Downpipe Thread? I searched on the term and there are pages of results.

Based on reading some of these results, there is only one AZ user who was able to achieve demonstrable emissions readiness and that was with a 400cell Redstar. However, there are other posts describing long-term reliability issues with the RS cat.

Has anyone else been able to achieve full emissions readiness?


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[SHCKR]

Which thread is The Downpipe Thread? I searched on the term and there are pages of results.

Based on reading some of these results, there is only one AZ user who was able to achieve demonstrable emissions readiness and that was with a 400cell Redstar. However, there are other posts describing long-term reliability issues with the RS cat.

Has anyone else been able to achieve full emissions readiness?


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I'm guessing the main two I'm referring to are:

https://r.tapatalk.com/shareLink/top...ink_source=app

https://r.tapatalk.com/shareLink/top...ink_source=app

First one should provide some insight on your Redstar purchase decision making process

[RogosMcGee]

I'm guessing the main two I'm referring to are:

https://r.tapatalk.com/shareLink/top...ink_source=app

https://r.tapatalk.com/shareLink/top...ink_source=app

First one should provide some insight on your Redstar purchase decision making process

I'll have to read those two threads. I've been trying to do diligence on Redstar because some people recommend them very strongly and they're basically your only option if you want an aftermarket downpipe and still want to be US emission compliants. So far from my own research here I've only found one "bad" experience (user 4-ring-sleepers), it was on an SQ5, but as he would be the first to acknowledge he was running stage 3 with an e-blend and pushing a lot of things -- his cat ended up deteriorating. I've been in communication with Redstar. At least for the 400 cell they're sourced in Canada and it sounds like they're assembling in the US. Lead time right now is 3-4 weeks. Again, I'll check out those threads.

[Kedawerx]

Thanks. I saw the first one.

Here is the thread in which a guy posts screen shots of readiness with a RS 400:

https://r.tapatalk.com/shareLink/top...ink_source=app

This is the only mention I’ve seen of someone actually meeting emissions testing requirements.


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[Daaavid]

I just ran this scenario by my buddy and he was like "I don't see what the problem is: go stage 2 and get a catless downpipe for free" lol. But there's some truth to what he's saying, right? If 034 and IE are mainly insisting on putting in an aftermarket downpipe to avoid people complaining that their stock cat was fried over time, why not just go stage 2 on the stock cat and let what happens happen, 10,000 miles later, congrats, you have a catless downpipe in an OEM housing -- I know 034's tune blanks the CEL anyway. I'm sort of joking not joking on this. I've been investigating RedStar downpipes which seem by every indication like great products but they're also expensive as hell for what seems like negligible gains.

I know you've crossed the whole "run the stock cat until it implodes" idea off your list, but do you actually know what happens when a cat clogs?

Just imagine yourself drinking a nice glass of water, now imagine you stop for a quick second to catch your breath, and then someone shoves a handful of dry paper towels into your mouth, and then you resume drinking water without chewing. That's basically what a deteriorating/failed cat is. You're choking the motor, increasing exhaust gas temps, and exponentially raise the risk of you blowing up the motor/turbo. You'll get flashing CELs, misfires, and inconsistent or no acceleration at all. Not a fun time. Oh yeah, the failed cat material has to go downstream still, so you might get a rattling exhaust/muffler if you were pushing it hard and it happened to implode at speed.

BTW, ITT, are we looking to be compliant to the federal government or looking to pass emissions? Because if we're looking to pass emission inspections, then there are other routes you can take to run catted/catless downpipes with a mini-cat and still pass. Either way you look at it, you'll still need to flash back to stock or stage 1 so the emission system in the car will have a chance to "ready" or "fail" for that matter.

[RogosMcGee]

BTW, ITT, are we looking to be compliant to the federal government or looking to pass emissions? Because if we're looking to pass emission inspections, then there are other routes you can take to run catted/catless downpipes with a mini-cat and still pass. Either way you look at it, you'll still need to flash back to stock or stage 1 so the emission system in the car will have a chance to "ready" or "fail" for that matter.

I have a ‘21 B9.5. I am one of what I’m assuming is many people here who were running EPL stage 2 with just an intercooler (I put on APR) and intake (ditto) because EPL didn’t require an aftermarket downpipe to go stage 2. With all the drama going on with EPL (and some reports of blown OEM cats) I’m leaning toward switching over to 034 stage 2, especially since they just released their B9.5 TCU too, but I need a downpipe to do it.

I’d like to put in a HFC rather than going catless because I don’t want the smell or noise—I’m interested in the performance but don’t want the car to get crazy loud. Ideally I’d like to install something that will let the car PASS an OBD emissions check (I’m in a Midwest state); I don’t care whether it’s actually emissions compliant but I want to be able to roll in to the testing center and pass versus going through the hassle of having to swap back the stock pipe every couple years. I don’t know if I’ll still have the car when it’s time to start testing (4 years from model year) but I figure it’ll help with resale regardless. The only option I’ve found that fits that is the Redstar 400 cell (and I like that they have heat shielding) but if there are other options I’m all ears, especially given what appears to be Redstar’s very mixed reputation here (and frankly there are even reports of Redstar 400 cells still throwing CELs).

Any advice is appreciated; the number of downpipe options for this platform is significant and it can be a little overwhelming.

[oesman]

Any advice is appreciated; the number of downpipe options for this platform is significant and it can be a little overwhelming.

AFAIK the Redstar unit you referenced is the only one known to be able to pass emissions while maintaining an actual catalyst. All the other cat-ed options I've seen don't pass. The emissions self testing seems to be quite sensitive on this platform. Many other cars I've owned, including a newer one than the B9, were fine with aftermarket racing/non-CARB compliant cats. Not sure if this is VAG/Audi's response to emissions scandals or if this is coming to other newer cars or maybe it's just a scheme to sell $4,000 OEM replacement catalysts. I used to always tell people to just get an aftemarket cat when their cat started to fail, no need to spend thousands of dollars on your old car, won't work on this car though.

[S4UCE]

Aside from smell and emissions concerns, does anyone have opinions or videos of catless on a fully stock exhaust? I’ve seen a couple with resonator delete but never full-on factory catback

[oesman]

Aside from smell and emissions concerns, does anyone have opinions or videos of catless on a fully stock exhaust? I’ve seen a couple with resonator delete but never full-on factory catback

Hmmmmm, I literally typed in "B9 downpipe stock exhaust" into youtube and this was the first result:

https://www.youtube.com/watch?v=GFknFQdUyvk

:-) Youtube works in weird ways though, their search algorithm and UI is getting progressively worse. It clearly weighs your recent viewing patterns and interest over the exact search term itself. So the results you get are sometimes total crap. After a few popular results they just start showing you other content that it thinks you might want to see. So unless you scroll all the way to the bottom it won't show you all the other results that match your query. You have to wade through all the "for you" and "related" recommendations first.

Also found this guy, but he titled his video poorly: https://www.youtube.com/watch?v=1NmEYXClJ50

Overall I think its def going to be louder, but not as bad with the stock resonators in. The mid resonator is pretty big.

[S4UCE]

You can say that again! I just scrolled down my search history and repeated the exact search term. The video you posted was the second result amongst a bunch of videos I’ve already viewed. Refreshed the results and that video disappeared into the abyss.