High Flow Cat vs Test Pipe on B9 S5

[18B9S5]

Hello all, from what I’ve gathered, this is a common topic in these forums.

Thus, my question may come off slightly on the ‘stupider’ side…

Is the High Flow Cat and Test Pipe considered a downpipe?

I am looking on CTS Turbo website for a downpipe, and I dont know which is which because nothing is labeled ‘downpipe’ for my model year.

Any help is appreciated as I am not thoroughly knowledgable on car parts, I just like backfires and crackles :)

[ToroTheShibe]

My buddy with a b9 s4 calls it a test pipe where I would have called it a catless downpipe.

If you’re looking for the piping that is between the engine and your exhaust, it’ll be the product that has two pipe leading into a giant opening. Looks like a funky Y

[sbruno624]

Yes they’re the same thing. A test pipe will 100% throw a CEL, and will fail emissions. CTS uses cheap cats however so those will also throw a CEL but will not smell as bad. If you want a replacement downpipe that won’t throw a CEL and will pass emissions you’re going to need either the 6” GESI cat or the 300 cell HJS. I’m sure people will tell you you can use spacers to pass emissions but that’s never a given.
Personally for my S4 I just ordered a Redstar Downpipe with the 6” GESI CAT because dealing with emissions wasn’t worth it. It will still fart, and may honestly drone less as well


Sent from my iPhone using Audizine

[18B9S5]

Thank you for this explanation.

Now I am stuck between the CTS High Flow Cat and the Redstar Downpipe.
What made you choose Redstar over CTS?

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Thank you for this explanation!

[QuickHandCam]

Thank you for this explanation.

Now I am stuck between the CTS High Flow Cat and the Redstar Downpipe.
What made you choose Redstar over CTS?

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Thank you for this explanation!

As stated, CTS uses a cheap Catalytic Converter. It'll do the job, but the design of them is poor in reducing emissions. Also, it will eventually start falling out years down the road due to the construction of the Cat.
This downpipe does not use OEM style heat-shielding and will affect performance due to heat. (Problematic on a "Hot"-V engine setup as the B9 S4/S5's have. Turbo in the V, on-top.)

With Redstar you have the option of whichever Cat you want, sizing, etc. The cats used with Redstar are actually "top-of-the-line". HJS having a "slightly" better design shape of the catalytic converter, but using just as good as materials as GESI. Also, you have the option to install OEM style heat-shielding (GET THIS, NO QUESTIONS ASKED).

If you wanna be cheap, buy cheap parts; nothing wrong with saving money, but I would "highly" recommend going the Redstar downpipe route and really configuring it out how you want it to be.

[torinalth]

figured i'd tag on to the redstar question. If i was reading it right its asking for 2-3k for a catted downpipe depending on options selected. I've never been one to shy away from spending money on my cars, but I'm not sure how i could justify this much for a catted pipe.

EDIT: Guess I'm missing something in general, but why the hell is the downpipe for this platform 2-3x more expensive than any other platform i've owned so far. Redstar i suppose is slightly on the pricier side compared to its direct competitors, but within the range..... so what's so different with the B9? my bmw one was ~950 msrp and was ceramic coated with a high end 200cell cat, and people thought that was expensive for the pipe.... so the platform change sticker shock has me a bit out of sorts, insight?

[BrisAudi]

figured i'd tag on to the redstar question. If i was reading it right its asking for 2-3k for a catted downpipe depending on options selected. I've never been one to shy away from spending money on my cars, but I'm not sure how i could justify this much for a catted pipe.

EDIT: Guess I'm missing something in general, but why the hell is the downpipe for this platform 2-3x more expensive than any other platform i've owned so far. Redstar i suppose is slightly on the pricier side compared to its direct competitors, but within the range..... so what's so different with the B9? my bmw one was ~950 msrp and was ceramic coated with a high end 200cell cat, and people thought that was expensive for the pipe.... so the platform change sticker shock has me a bit out of sorts, insight?

Totally agree, $2-3k is too high. I also have a B58 and yes we have a lot to choose from when it comes to downpipe on that platform. Keep in mind thou, the shape of the cat on the audi definetetly doesnt help with keeping the cost down but ideally $1200-1500 will be acceptable in my books. The 034 catted down pipe seems like the one to get for price and quality ATM.

[PuxedoTopato]

Thank you for this explanation.

Now I am stuck between the CTS High Flow Cat and the Redstar Downpipe.
What made you choose Redstar over CTS?

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Thank you for this explanation!

Take a look at the 034 Motorsport high flow cat! It’s cheaper than the Redstar, heat shielded, and man does it make the car sound good and drive even better! 034 puts in a ridiculous amount of research and engineering into their products and they don’t skimp on anything. Just please don’t put a CTS down pipe in your Audi… The cat will give you the biggest performance gain out of any bolt on, so don’t get a cheap one

[SHCKR]

Take a look at the 034 Motorsport high flow cat! It’s cheaper than the Redstar, heat shielded, and man does it make the car sound good and drive even better! 034 puts in a ridiculous amount of research and engineering into their products and they don’t skimp on anything. Just please don’t put a CTS down pipe in your Audi… The cat will give you the biggest performance gain out of any bolt on, so don’t get a cheap one

Idk man, I think the consensus is, and this is coming from the tuners, that the DP really doesn't do much on this platform except add noise.

[Deezbluballz]

Does the 034 Motorsport high flow cat trip a MIL light? Or is that hit or miss with those?
B9 RS5

[QuickHandCam]

Does the 034 Motorsport high flow cat trip a MIL light? Or is that hit or miss with those?
B9 RS5

It does! I'm sure you could buy a spacer for it, but I'm pretty sure 034MS doesn't condone that.

[PuxedoTopato]

Idk man, I think the consensus is, and this is coming from the tuners, that the DP really doesn't do much on this platform except add noise.

Idk what tuner reps you’re talking to, but a high flow cat yields excellent hp gains. I held the stock and 034 HFC side by side, and you can literally see how much more flow you have. I drove it just before, and after the install, and I could absolutely feel the gains. The stock cat on the B9 platform is highly restrictive. Take a look at the dyno chart on the 034 HFC, it speaks for itself!

[SHCKR]

Idk what tuner reps you’re talking to, but a high flow cat yields excellent hp gains. I held the stock and 034 HFC side by side, and you can literally see how much more flow you have. I drove it just before, and after the install, and I could absolutely feel the gains. The stock cat on the B9 platform is highly restrictive. Take a look at the dyno chart on the 034 HFC, it speaks for itself!

Just relating what I've seen on the forms over the last few years for this platform. I personally run a DECAT, so I don't necessarily disagree, but so far the data I've seen proves otherwise. Something to do with stock DP not being restrictive enough for stock turbo.

[PuxedoTopato]

Just relating what I've seen on the forms over the last few years for this platform. I personally run a DECAT, so I don't necessarily disagree, but so far the data I've seen proves otherwise. Something to do with stock DP not being restrictive enough for stock turbo.

From a stock perspective, I can see how the gains would be less. But I’ve had a JB4 and intercooler since a couple weeks after I got my car, and the 034 E85 tune before I installed the cat. When you are putting out more power than stock, then the gains from a high flow down pipe are much more pronounced. I guess if you’re blowing air lightly through a tight screen vs high flow/no screen, it’s only a bit better flow than the tight one. But if you have a leaf blower (tune) blowing the air, then you start to really see the difference an HFC or catless down pipe makes. If that makes sense.

[QuickHandCam]

Just relating what I've seen on the forms over the last few years for this platform. I personally run a DECAT, so I don't necessarily disagree, but so far the data I've seen proves otherwise. Something to do with stock DP not being restrictive enough for stock turbo.

Do you have the catless downpipe mated to the stock cat-back?

Curious to hear what this sounds like and if there is any drone in D and/or S. Wife HATES drone and I don't feel like listening to her bitching for the next X miles until we get to the destination.

[SHCKR]

Do you have the catless downpipe mated to the stock cat-back?

Curious to hear what this sounds like and if there is any drone in D and/or S. Wife HATES drone and I don't feel like listening to her bitching for the next X miles until we get to the destination.

Check out the VPS thread, I have sound clips in there. If you read the thread you'll also see my progression with sound/drone, etc

[QuickHandCam]

Check out the VPS thread, I have sound clips in there. If you read the thread you'll also see my progression with sound/drone, etc

I just checked it out. Seems like you were on stock exhaust with VPS front res delete.
Was wondering if you were catless at the time of the VPS or before, but I didn't see the information there. Maybe I overlooked it, however.

[SHCKR]

I just checked it out. Seems like you were on stock exhaust with VPS front res delete.
Was wondering if you were catless at the time of the VPS or before, but I didn't see the information there. Maybe I overlooked it, however.

VPS was first, all good, no drone. Added DP, drone galore regardless of drive mode. Got rid of VPS, kept the DP, deeper, sportier sound, minor done in dynamic only (keep individual exhaust setting in auto for daily hwy driving). No drone in this setting: