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B6/B7 Audi S4 Piggie Pipes / Downpipes

B7 Audi S4 Piggie Pipes

One of the best, and certainly most cost-effective, ways to add power to your B6/B7 Audi S4 with the 4.2 V8 is the downpipes. The factory system contains two sets of catalytic converters on each downpipe, a pre-cat and a main cat. The pre-cat in particular robs the engine of power because it is very close to the engine and creates turbulance/disruption very early in the exhaust flow out of the engine. This thread on Audizine by Justincredible goes into greater detail as to why the downpipes are so restrictive and why its quite possibly the best “first” performance mod to do to your B6/B7 Audi S4. After some light reading of this thread, I was excited to go about this mod so I recently had my pre-cats removed/turned into piggie pipes by a local shop, Parts Score in Tempe, AZ. The mod definitely opened up a little extra power and increased the exhaust sound, so I wanted to share my experiences & thoughts and research on the mod here for others to enjoy. If you don’t want to read the whole thing – I’ll skip to the point…it’s a great mod and lives up to the hype!

My B7 S4 on the Rack

There are a few options in terms of addressing the restrictive downpipes of the B6/B7 S4:

  • Piggie pipes – taking the OEM downpipes and punching out/removing the catalytic converter material, allowing air to pass through more freely
  • JHM Longtube Headers – these are supposed to be the best option performance wise, but also quite expensive at ~$3,000 and are made to order
  • Aftermarket downpipes – Milltek, Fast Intentions and a custom solution by a fellow named TrexTurk all remove catalytic converters and come in larger pipe diameter for improved exhaust flow and sound, and range in cost from about $500-2000 depending on options and the source

O2 Spacers

Why I went with Piggie Pipes:

One downside to going with a fully catless system (such as JHM and other aftermarket headers) is that your exhaust will be both louder and potentially emit a bit of an odor, as well as a higher cost to purchase the parts. My A4 had a “test pipe” which eliminated the catalytic converter and essentially did the same thing as the downpipe solutions for the 4.2 V8 on the S4; the odor kind of bothered me on my A4, and I wanted an exhaust setup that was pretty tame (both sound and smell wise) for daily driver purposes, hence why I went with a Milltek resonated system to begin with (the quietest system for the B7 S4 I know of).

The other main advantage to using the OEM downpipes was that I could only remove the pre-cats (which rob the most power) while keeping the main cats, maintaining some sound & odor dampening as well as keeping my emissions somewhat reduced. Another advantage was cost – I had my downpipes removed, gutted, and reinstalled for less than $500, which is less than buying even the cheapest downpipes on the market. Lastly, one more perk of going for piggie pieps is the lack of a Check Engine Light as a simple  O2 spacer setup could avoid a CEL warning in this case. The CEL for aftermarket setups can be removed via a tune, but I haven’t tuned my car yet and am I’m delaying a tune a little while longer to keep my warranty in tact. Parts Score, the shop that completed this work for me, found a trick using O2 spacers and a little “secret sauce” to avoid a CEL, and I’ve been running this way for 500+ miles with no issues. Other users report that a CEL occurs about 50% of the time with this method, but various options such as using two sets of 02 spacers or modifying the spacers can increase your likelihood of avoiding a CEL.

OEM Downpipes

Sound & Performance Gains of Piggie Pipes:

The sound is slightly raspier and metallic – in a good way of course. I’d say the exhaust is about 10% louder at normal speeds and maybe 20% louder at wide open throttle. I need to get a video or sound clip, and will update this post when I do. I expected the removal of the pre-cats to make the exhaust louder than it did to be honest – its certainly a little louder, but not dramatic or even noticeable to most people. I didn’t have an opportunity to dyno the car before and after, but I can tell you that it feels faster and more responsive to the throttle, especially when really hammering it.

Overall, I’m really happy with this mod and it lived up to all of the reading & reviews that I found prior to going with it. The improvements in performance and sound at a nominal cost make it tough to beat, especially for a car like the B7 S4 which typically requires a lot of money to make modest improvements in power. I highly recommend this!

Nick Roshon

Nick has been an Audi owner and fanatic for the last 10 years, and started Nick's Car Blog in 2009 to share DIYs and pictures of his A4. Currently he drives a 2012 Audi TT-RS, and has previously owned a B7 S4, B7 A4, and an 82 Audi Coupe (GT) LeMons race car. In his day job, Nick is a digital marketer and lives in San Diego, CA, USA.


  1. Do you get any drone with the Milltek resonated catback and the piggy pipes? I just installed a full FI system (with cats and resonators) but it is droning hard 1500-2000 rpms.

  2. I’m pretty sure the Milltek resonated exhaust is the quietest on the market for our cars – it’s so quiet that it sounds as if it were a (performance oriented) OEM exhaust. Most people actually don’t like the exhaust as it’s too subtle…but to me, it’s drone free, still has some added noise, and is perfect for daily driver use. So no drone whatsoever, it just may be too quiet for some.

  3. i have a question about this topic havin the precats turn into piggie backs you mention something about the o2 sensors needing spacers is this after you have the precats gutted the sensors need some type spacers for the mil light not too come on ?what type of spacers were could i get them if i want to have my pre cats done .thanks

  4. Hi Ruben – yes, the spacers are for the O2 sensors so they get a cleaner reading and don’t through a Check Engine Light. You can do a search for O2 sensor spacers and they’re all pretty much universal fit, or you could find a shop to do it for you. The other option is to get a tune like JHM which removes the warning light, in which case you don’t need to bother with the sensors in the first place…

  5. I was doing some research on this topic too and was curious if you could do a video or something because i was planing on doing this to my audi a4 3.2L.

  6. Nick, did you drill out your double spaced non-foulers like a lot of the write ups show?

  7. I have a 2006 S4 also and i’m strongly considering buying the JHM downpipes by sending mine in for a cheap $245 but i’m wondering about the added costs of removing/shipping/installing to see what it will amount to. About how many mechanic hours did it take you to perform this mod?

  8. It should take less than an hour for a local shop to punch out the cats once they have them off and a few bucks for hazardous material disposal, so very cheap, but the bigger challenge is finding a shop willing to do it – most shops will shy away from doing it given the grey area of doing so from a legality/smog standpoint.

  9. Hey, Nick I recently purchased the JHM piggie downpipes for my B7 S4 automatic, Going to have them installed in June after I’m back from vacation with pair of new rear Bosch O2 sensors (one is faulty). There was no mention about needing O2 spacers and I’m concerned about keeping the car emissions legal for passing routine annual state inspections in Texas. Is this something I should have added when I do the install? I’ve had a check engine light about the smog pump but replaced it and the relay and thinking new rear O2 sensors since one is faulty should clear up those misreading codes but don’t want the upgraded downpipes to interfere in the process. I’m all about upgrades but prefer keeping things simple and as legit as possible for state inspection issues. Thoughts on the spacers, yes/no/maybe?

  10. Maybe it want need spacers after all since I just read on JHM site “Both OEM modified “piggie” downpipes with OEM main cats and relocated rear O2 sensor bungs.” Maybe they relocated them to prevent CEL warnings for the current piggie pipes. Just trying to make darn sure I get it right the first time installed this June.

  11. If you have the JHM tune it will cancel out the CEL for O2 sensors regardless, so you won’t need spacers. I had my piggies installed before the tune, so the spacers were (likely) necessary to eliminate the code on a stock tune. I can’t say for sure if you can’t pass without spacers, but it seems unlikely from what I’ve read.

  12. Well, I’m planning on getting the JHM Tune as well later this summer anyways but was holding off till I get their upgraded manifold & throttle body installed as a finishing touch but I’m sure the tune can be adjusted as I go along the way. Basically, I think your saying the JHM tune either disable the CEL or changes the expected range the 02 sensors see as acceptable as not to throw a CEL? Is that the correct assumption? I just assume that even with the JHM tune that the car will still use the 02 Sensors right or will it just disregard them? ……for me in Texas as long as the ecu shows ready status, emissions are within acceptable levels and no CEL light on dash….than I should be good to go to pass inspection I would think. That’s my end goal

  13. The tune will be the same file regardless of whether you have the IM or not, so I’d just go for the tune now when you do piggies…that will prevent the CEL and keep you kosher for your inspection – Arizona was the same way, they just needed to see ECU ready and no CEL on dash.

  14. Cool, really good to know, I’m almost done with my car mostly and really pleased with it thus far but ridding the CEL and getting my first legal inspection sticker next year (cough, cough) is what I want. Damn smog pump/02 CEL is like driving around with a glaring yellow mosquito constantly in your face. Just the manifold, throttle body and brakes upgrades for the serious upcoming left over work. Like you definitely updating the steering wheel and RNS-E to newer version with brushed knobs. Thanks again ; )

  15. Hello…i recently purchased a 2006 s4 Quattro v8 with 172000miles and the engine light came on reading codes p0431 and p0421 stating the 02sensor and cat what should i do and this happened after putting in the cheaper gas. Someone tod me to add bg44k to help clear it, what do you think?

  16. It’s possible some bad gas could have caused it, but if a fresh tank doesn’t solve the issue I would research those codes more heavily. If the cats are failing you will want to address before they fall apart completely and get sucked into the engine. Piggie Pipes could be a good solution for you then…and 02 Spacers as well 😉

  17. Much quicker way to purge out cheap gas, pick up small 5 gallon of VP racing fuel ms109 or something similar from local supplier or track. The105 octane will help boost the diluted gas you might have. Will definitely clean out the engine flushing out possible bad gas faster. Either way wouldn’t hurt anything with the higher octane if this is not your problem. You said you just purchased this car, like last week, a few months etc? Maybe it already had those codes or issues but they were cleared before purchase? I don’t know, just bouncing ideas for you….

  18. Whats up Nick i enjoy your blog. Im having a bit of a problem. I own a b7 RS4 with JHM tune piggies ECS h pipe. Bought the car with 90k. Idid carbon clean at 94k. Now at 110k i did timing chain service and noticed inside intake i need carbon cleaning again. CEL is on P2234 . process of elimination i plan on changing coil packs and front 02 sensors and plan on another carbon clean again. Any suggestions would be helpful and keep up these posts. You’re a life saver

  19. Oh man, wish I could help more but I’m not super familiar with RS4 carbon issues. I’d start a thread in the Audizine RS4 forum and get some inputs!

  20. Nick would cutting them out and welding another pipe onto the exhaust in place of the secondary cats be at the same ponit in a performance and noise standpoint. I just don’t understand why one would go through all that when they could just remove them lol with a replacement pipe, the old school 2ndary muffler delete for all the AMG fan boys haha

  21. I have a b7 rs4. I gutted my top converters and deleted them with a tune. Youre going to get a growl if yy go this route. Plus i had done ECS h pipe. You can feel less restrictions

  22. Yeah you could just cut and weld in a new piece of pipe, that’s actually slightly better…just typically more expensive and more difficult than just punching out the cats and putting back in place. In California (and some other states) where they do a visual inspection for smog it is nice to have it look OEM like there still might be a cat converter in place 😉

  23. Hey NIck, I have a B7 S4 and I want to gut my precats as well. I dont have plans on getting a JHM tune just yet and I am wondering if you can simply reinstall the O2 sensors with foulers OR do you need to relocate them to after the main cats?

    Also, are the foulers a “plug-n-play” install or do they need to be modified?

  24. You definitely need foulers, and sometimes it works sometimes it doesn’t. My shop did some magic to make it work with just foulers, no tune, and in stock location, but you might need to play with it some.

  25. The Vibrant ‘J’ style O2 Spacers work very well in my experience. Part #11619

  26. i have 2005 audi s4 b6 tip tronic I’m plaining buy the AWE touring catback exhaust, Can i get the JHM downpipe and bolt on together??

  27. You should probably call JHM to confirm (they’re really helpful on the phone, ask for Dru and tell him I sent you) but as long as both are 2.5″ pipes I don’t see why not…even if one is 2.25″ (standard piping diametere) I believe they have an adapter to upsize.

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