Question about gutting out the pre cats?

[Ben@SpeedBarn]

Ok. I think I would like to do this. Any links to the directions on this? What benefits in power, spoolup, and sound would i get with stock exhaust? Thanks!

[cj-S4]

I did a small write up in our tech section. It should sound nice. Spool up will be quicker, and you will have some nice torque gains. Generally aftermarket DPs are a bigger pipe yielding higher HP gains, staying with the stock smaller pipes will give more torque. But all and all the end result will be close to that of an aftermarket pipe.

[EricPA]

Commonly referred to "piggie pipes" on AW. Just stock DP's with gutted pre-cats and relocated 02 sensors. I'll be installing some soon on my car. "Word" is they yield roughly 90% of the gains vs. typical aftermarket DP's but are half the price.

[Ben@SpeedBarn]

Do you guys think this is a worth while mod keeping the stock exhaust? I'm tired of loud cars. As much as I love the sound I love the quietness of driving the S. Wouldn't mind being able to hear it a little more...especialy at WOT. Has anyone done piggie pipes with the stock exhaust with no plans of larger exhaust ever?

[Ben@SpeedBarn]

CJ i get a message that I don't have the rights to view that page when I click on your link...???

[XpondS4]

Me too CJ.....hows the car comin along BTW?

[EricPA]

Like you I'm not a fan on loud exhausts. My Borla sounds very nice and it's not very loud at all. DP's are not suppose to make exhausts that much louder so you'll be ok with the stock exhaust and I'll be ok with the Borla. You can take a listen to my car anytime you want. I saw your sweet ride twice last weekend in your work parking lot. I'll be cruising through the SS this weekend as well so let me know if/when you'll be around.

[cj-S4]

Sorry, I keep forgetting that I see things you guys don't. Seems we haven't launched that section public yet? Anyway,,, heres a copy&paste

Things needed
- Nice Vise hard mounted with some room to move around it
- Drill with a 3/4 inch Spade Bit (the bits are for wood) and a Metal HoleSaw (I think it was 3/4" but measure the O2 sensor nub to be sure before you drill)
- Hammer and a Punch
- Long large straight Flat Head Screw Driver (that you don't care about damaging)
- Patience, and maybe a few bandaids

Parts
- O2 Sensor Nubs (small threaded nubs you weld into the pipe to accept an O2 sensor)
- Pipe Plugs (same thread as O2 sensor to screw into then weld to plug the old hole)

Before removing the Downpipes (DPs), look at where the main cat O2 sensor is. Now pick a spot about 1 inch behind the main cat that you will be able to have the O2 sensor located to with no interference with the body of the car or anything else. Mark the spot with a punch.

Step 1
Remove Downpipes.

Step 2
Clamp one of the pipes into a vise so it is held with the main cat up in the air, so pieces of the pre cat don't fall into it.

Step 3
Use screw driver and hammer, pound the screw driver in between the precat and pipe inner, get it in an inch or so and wiggle it up and down to break the precat away from the inner pipe, keep working around the precat and deeper into it. Eventually it will become kinda loose.

Step 4
Use drill and spade bit to drill into the precat, the chunks will start falling out (make sure you have the main cat up in the air at this point).

Step 5
Keep working with the drill and screw driver till you get it all out.

Step 6
Repeat on other pipe.

Step 7
O2 sensor relocation. The sensor before the precat stays where it is. The sensor infront of the Main cat is the one to move, plug and weld its old location.

Step 8
Drill with the hole saw at the locating you marked before removing the DPs.

Step 9
Weld the new O2 sensor nub into the new hole behind the Main Cat, make sure it is sealed completely around the hole.

Step 10
Repeat on other DP.

Step 11
Reinstall, you will have to untie the sensor wires to get enough slack to move them to the new location, then retie them up.

[Ben@SpeedBarn]

Ok a couple questions.

There are only 4 O2 Sensors? From the origional locations it would seem you could remove the main cats and not recieve a check engine light then?

Wouldn't that be easier than the removing the precats then? Are the pre cats more restrictive? Why do we have them? MOst cars don't do they? I know my cousins 3k VR4 had them. Is it a turbo thing?

The directions you described will not throw a code correct?

Where do you get the plug and new bung? Autoparts store? Audi?

Are the downpipes stainless? Just wondering cause I have never welded with stainless before.

I've gutted out regular cats in older trucks this way so I understand what you're talkin about.

Good write up Chris

Thanks.

[quicksilver_S]

Will gutting the dp cause a problem passing emission testing?

[cj-S4]

Originally posted by quicksilver_S
Will gutting the dp cause a problem passing emission testing?

No

[cj-S4]

Originally posted by Ben@SpeedBarn
Ok a couple questions.

There are only 4 O2 Sensors? From the origional locations it would seem you could remove the main cats and not recieve a check engine light then?

Perhaps, but I never tried it.

Wouldn't that be easier than the removing the precats then? Are the pre cats more restrictive? Why do we have them? MOst cars don't do they? I know my cousins 3k VR4 had them. Is it a turbo thing?

Not really, you would have to cut them out, then weld new pipes in. Also,, yes the precats are more restrictive, when you take it apart and get to see the "precat" you will wonder how anything makes it through there.

We have precats to aid in emisions. The precat makes the car warm up faster, thus burning clean sooner. I do believe it is a turbo car thing only,, and used by the manufactures to pass certain EPA tests. It wouldn't surprise me if the Euro versions have no precats,, but I don't know.

The directions you described will not throw a code correct?

No codes, as long as you relocate the O2 sensor.

Where do you get the plug and new bung? Autoparts store? Audi?

Autoparts store, I got mine at CarQuest (formerly Beacon Auto parts) You may have to call around because it won't be a normal item. Most any parts supplier that deals with exhaust and mechanic shops directly,, will have them. I paid 5 bucks each for them.

Are the downpipes stainless? Just wondering cause I have never welded with stainless before.

No. Mine had some rust on them, welded fine with a Mig welder.

[XpondS4]

Do you know how emissions tests compare between the UK and the US. Like ....do you think its gonna cause me problems on emmisions whereas it would not on your DOT testing....is it less strict,more or the same???

[Ben@SpeedBarn]

Thank's Chris!

You just seem to know everything!

I'm guessing the dealer probably won't like this and it would void the warranty of the cats at least. Maybe I will wait till next spring to do this after my warranty is over and audi assured kicks in.

How is your car coming by the way?

[cj-S4]

Originally posted by XpondS4
Do you know how emissions tests compare between the UK and the US. Like ....do you think its gonna cause me problems on emmisions whereas it would not on your DOT testing....is it less strict,more or the same???

I don't know what your procedures are over in the UK. But I do know that generally they are less strict than US standards.

[cj-S4]

Originally posted by Ben@SpeedBarn
Thank's Chris!

You just seem to know everything!

I'm guessing the dealer probably won't like this and it would void the warranty of the cats at least. Maybe I will wait till next spring to do this after my warranty is over and audi assured kicks in.

How is your car coming by the way?

Nah, nowhere near everything,, but thanks.

Yes they wouldn't like it, but they would also probably not even know. Unless they had to get in there for something, which would be unlikely. Since they will avoid that job till the thing is dead.

My car, it has alot of dust on it. My intrests as far as money spending have swayed toward more 2 wheel things. But I have been saving and,, hopefully will have the engine at least back in by the end of summer. But I really am starting to miss my S4. Plus I have some big bids out,, if they go through,, well then,, but I won't count on them till I actually get the jobs.