B5 S4 & RS4 Exhaust Options

[DavidT]

There has been plenty of discussion on these lateley, so I wondered if there are any objective figures about the gains.

My car is stage 3 and I have milltek downpipes with 100 cell cats with a milltek dual. Works well but it booms a bit at low rpm's (below 2.5k) but is very quiet at motorway speeds. The noise in the car at high revs is superb, everyone has commented on it. I had a single with these downpipes before and thought it was a bit too quiet (I know, it seems a mad thing to say about an Audi!) I also think that the dual has freed the car at higher revs, I noticed immediately it was fitted, but this could be my imagination.

So please post up any options you have details of with comparative info if possible.

[Nige_RS4]

I had an APR cat-back on my old S4 and it sounded far superior IMHO to the Miltek equivalent - not quite as noisy, but no booming = a more mature sound.

[DavidT]

I had an APR cat-back on my old S4 and it sounded far superior IMHO to the Miltek equivalent - not quite as noisy, but no booming = a more mature sound.

Ta Nige, was it a single or dual pipe ? (the milltek single does not boom)

[DavidT]

Options I am aware of:

S4 Downpipes - gutted pre-cats, 400cell main cats

RS4 Downpipes - gutted pre-cats, 200cell main cats

Milltek Downpipes - no pre-cats, 100 or 200 cell main cats (are the downpipes larger diameter?)

APR Downpipes - what is the spec?

Milltek S4 single & dual cat-back

RS4 cat back - standard item - an upgrade for the S4 ?

Other suppliers, including tuner specific - please list.

No custom one-off systems please, thread is for off the shelf systems.

[s4woody]

i have S4 dwn pipes no pre-cats no main-cats and milltek duel cat back..i love the boom..

[fletchie55]

I dont think you can attach an RS4 cat back to S4 downpipes as they're different lengths. You have to change both downpipes and cat back to std RS4 or nothing.

[PhilT]

The Sportec turbo back system on the RS4 is lovely. They gut the standard cats, refill, and reseal. Not too boomy, and as it is just stainless steel (not chrome) it has the rough and ready look. I love it.

[quattrosteph]

with my milltek non resonated the boomy sound(wish is a real pain ) was gone when my precats were removed !!!????How strange is that!! But the way it is fit is important too.

[ZeroK66]

Hi Guys,

Well my setup is standard S4 downs with no pre-cats and 400cel cats + a miltek 3" single. Estimated power anywhere between 430 & 460 with the MRC500 parts and a 3.6sec FATS. Seems the Standard exhaust setup and a miltek catback is not that restrictive, but I have found the point where it must be upgraded.

Off the shelf items - MRC offer 3" downpipes with dual 2.75" exaust. This costs £1.2k and does not include CATS. I suppose you could call this an off the shelf item.

I will try and rolling road before and after whatever I choose to install... this should show exactly how much of a restricter my setup is.

[QuantumJohn]

I dont think you can attach an RS4 cat back to S4 downpipes as they're different lengths. You have to change both downpipes and cat back to std RS4 or nothing.

Joe is right. You can't attach an RS4 cat back to the S4 downpipes because they are different lengths i.e. they join in different places.
Additionally the wider oval shapped tips on the RS4 exhuast don't fit within the cut out on the rear bumper of the S4. This is also affected by the fact the RS4 tailpipes are spaced wider than the S4 ones to accomoodate the oval tips.
However, it does fit if you cut the tips off and weld on the ones from a Gold R32

John

[DavidT]

I dont think you can attach an RS4 cat back to S4 downpipes as they're different lengths. You have to change both downpipes and cat back to std RS4 or nothing.

Joe is right. You can't attach an RS4 cat back to the S4 downpipes because they are different lengths i.e. they join in different places.
Additionally the wider oval shapped tips on the RS4 exhuast don't fit within the cut out on the rear bumper of the S4. This is also affected by the fact the RS4 tailpipes are spaced wider than the S4 ones to accomoodate the oval tips.
However, it does fit if you cut the tips off and weld on the ones from a Gold R32

John

CliveH - how did you fit yours then

[MarkB]

Clives hangs lower than the bumper.

[Nige_RS4]

APR DP's come with test pipes too! £/$ exchange rate is great at the moment.

Here's some more data ... http://forums.audiworld.com/s4/msgs/2424387.phtml

MRC also do a large bore full system, but I haven't heard it yet - not sure I want any boom or too much noise. I've still to put the Milltek twin on my car - it's been in my garage for 6 months!!

[rolskii]

I dont think you can attach an RS4 cat back to S4 downpipes as they're different lengths. You have to change both downpipes and cat back to std RS4 or nothing.

Also different dia. too ... about .25" larger,

I have rs4 pre-gutted d/pipes, 200 cell main cats, onto 3" single milltek, twin s/tip..
I made the conversion by modding the Y-pipe on the milltek, can now use my spare rs4 system if the milltek fails ...
so I got 3 boxes on it(well 4)... 2 cats, centre & back box .... wouldnt mind freeing it up a bit more, but dont want to get any noisier ....
Sounds good and not boomy at all

[Nige_RS4]

Ta Nige, was it a single or dual pipe ? (the milltek single does not boom)

Single!