SmokinS4™

1. Inner Diameter
2. Removal of Pre-Cats?
3. O2 sensor location fore and after cat? (if cats are doing their job, you won't get a CEL. Some tuners also will reprogram the chip to ignore this code too - ie test-pipe option-chips)
4. Test-Pipe Option?
5. Flex Joints?
6. Cat Type
7. Cost?

So now how does each option (that I'm aware of) stack up?

<b>Stock System</b>
Diameter = &lt;2.25" (I believe)
Pre-Cats = YES
O2 Sensor location fore and aft of cats = YES
Test Pipes = NO
Flex Joints = YES (metal mesh/bellows-type)
Cat Type = Pre = Metal, Main = Ceramic 400cel
Cost = Nothing, you already have them.

&lt;b&gt; Piggie Pipes - OEM with gutted precats&lt;/b&gt;
&lt;a href="http://www.vastperformance.com/products/exhaust.php"&gt;Piggie Pipes&lt;/a&gt;
Diameter = &lt;2.25" (I believe)
Pre-Cats = Not anymore
O2 Sensor location fore and aft of cats = YES, often relocated 2nd O2 sensor to behind main cat
Test Pipes = NO
Flex Joints = YES (metal mesh/bellows-type)
Cat Type = Main = Ceramic 400cel
Cost = stockers plus labor.
&lt;img src="http://www.vastperformance.com/images/piggies_web.jpg"&gt;


<b>APR</b>
Diameter = 3.0"
Pre-Cats = NO
O2 Sensor location fore and aft of cats = YES
Test Pipes = YES
Flex Joints = YES (metal mesh/bellows-type)
Cat Type = ?
Cost = $1499
<img src="http://ctny.audiworld.com/mark/s4/downpipes/DSC04667.JPG">

<b>AWE</b>
Diameter = taper from 3" to 2.5"
Pre-Cats = NO
02 Sensor location fore and aft of cats = YES
Test Pipes = YES
Flex Joints = YES (ball/socket joint)
Cat Type = 400 cell per inch Ceramic Matrix
Cost = $1595
<img src="http://www.awe-tuning.com/media/products/awe/awe_s4dp_sm.jpg">

<b>JP Engineering</b>
Diameter = taper from 3" to 2.5"
Pre-Cats = NO
O2 Sensor location fore and aft of cats = YES
Test Pipes = NO
Flex Joints = YES (metal mesh/bellows-type)
Cat Type = Carsound (400cpi Ceramic)
Cost = $1350
<b>ANYONE HAVE A PIC?</b>


<b>Milltek</b>
Diameter = 2.3" (60mm)
Pre-Cats = NO
O2 Sensor Location fore and aft of cats = YES
Test Pipes = NO
Flex Joints = YES (metal mesh/bellows-type)
Cat Type = continuous stainless steel cores 200cel
Cost = $1865
<img src="http://www.stratmosphere.com/milltek_s4_dpandcats_fullset_320.jpg">

<b>MTM</b>
Diameter = ?
Pre-Cats = NO
O2 Sensor location fore and aft of cats = YES
Test Pipes = ?
Flex Joints = YES (not sure what type)
Cat Type = ?
Cost = $6900 (part of there Stage 3 package)
<img src="http://www.avalonmotorsports.com/store/uploads/dpipes_s4_mtm.jpg">

<b>RS4</b>
Diameter = 2.3inch inner diameter
Pre-Cats = YES
O2 Sensor location fore and aft of cats = YES
Test Pipes = NO
Flex Joints = YES (metal mesh/bellows-type)
Cat Type = Precat-precious metal, main cat=ceramic 400cel
Cost = $3000 or $1200 used.
<img src="http://65.182.219.254/smokin_s4/RS4_DPs/images/DSCN1391.jpg">

<b>Tantrumwerks Split Downpipes</b>
Diameter = merge into a 2.5" pipe
Pre-Cats = NO
O2 Sensor location fore and aft of cats = YES
Test Pipes = yes
Flex Joints = YES (metal mesh/bellows-type)
Cat Type = ???
Cost = $1550 for stainless w/cats (other options available)
other note: divorced wastegate downpipes
<img src="http://www.tantrumwerks.com/images/s4dpt4.jpg">

<b>Autospeed</b>
Diameter = 3.0inch, tapers to 2.5 for most aftermarket cat-back exhausts
Pre-Cats = NO
O2 Sensor location fore and aft of cats = YES
Test Pipes = YES
Flex Joints = 3" Stainless Steel Braided Flex Joint.
Cat Type = 400cel ceramic cats
Cost = $1549.
<img src="http://www.autospeedperformance.com/Exhaust/dp.jpg">

<b>GHL Downpipes</b>
Diameter = 2.5
Pre-Cats = NO
O2 Sensor location fore and aft of cats = YES
Test Pipes = YES
Flex Joints = 3" Stainless Steel Braided Flex Joint.
Cat Type = ???
Cost = $1279
<img src="http://www.ecstuning.com/stage/images/product/iadmin/570_x450.jpg"><ul><li><a href="https://forums.audiworld.com/s4/msgs/718930.phtml">https://forums.audiworld.com/s4/msgs/718930.phtml</a</li></ul>

LCP

Autospeed DPs have ceramic cats

SmokinS4™

Thanks, updated. I would like confirmation on APRs, since I think they've gone thru some revision.

Chaka

Even if you have the sensors located before and after you can still get a check engine light if your cats are inefficient.

SmokinS4™

I edited the wording a little....better?

S4mig@PEB tuning

<img src="http://pictureposter.audiworld.com/54947/dplower.jpg">
and
<img src="http://pictureposter.audiworld.com/54947/dpupper.jpg">

by the looks its a 1 1/2 and a 1 3/4 that dumps into a 3 inch pipe.

DAP@EPL

and a 3" inlet. Check out Mark P's pictures.

-Dave Pramanik<ul><li><a href="http://ctny.audiworld.com/mark/s4/downpipes/">http://ctny.audiworld.com/mark/s4/downpipes/</a</li></ul>

Mike@VAST

stock main cats are 400 cpi too.

SmokinS4™

thanks - updated

SmokinS4™

thanks - updated