apparently ECS tuning is selling them now (or will be shortly). In all my experience w/ exhausts Corsa's quality seemed top notch (loved it on my Viper) and ECS has a group buy going on now.<ul><li><a href="http://www.ecstuning.com/stage/edpd/pagebuild_v2.cgi?make=Audi&amp;engine=V8&amp;model=B7%20S4 &amp;submodel=&amp;category=Exhaust&amp;subcategory=Corsa">ECS - Corsa exhaust</a></li></ul>

shows the inside cruising volume. 6th gear at 60 mph. NICE! I'm just wondering if there will be a loss in torque since it's a 2.5" pipe.<ul><li><a href="http://youtube.com/watch?v=B31EAii2bYA">Clicky!</a></li></ul>

personally, I like an exhaust to be a little louder so I would add downpipes to any exhaust that was put on an S4 but I don't think you would lose any torque with just the cat back... you wouldn't gain any but you probably wouldn't lose either.

Here's link to my Viper w/ a Corsa exhaust...<ul><li><a href="http://youtube.com/watch?v=u6WF8NCOHyI">Viper w/ Corsa</a></li></ul>

thus leading to a slight decrease in the torque around 3-4k rpm. It's better to go 2.25" That's what I hear, could totally be wrong.

how more back pressure gives you more torque.

so, if the stock pipe is 2 inches, you don't want to go higher than 2.25 inches to keep power similar. I've heard you will get more upper end power with 2.5 inch piping, but you lose some lower end power.

"A car like the S4 has a pretty well tuned exhaust with the correct back pressure etc, so you might actually loose power with these systems."

"If you think of the pipe as a river - the narrower the river gets, the faster the water flows. However, water may spill over the banks if it gets too narrow. The wider the river gets, the more water it can handle but the slower the river flows. Its all about matching the correct diameter to the volume of air flowing through the pipes..."

Like I said in the previous post, "That's what I hear, could totally be wrong."

The headers are a resonant system. In some exhaust systems, the amount of back pressure used can change the resonance point and RPM at which the torque peak is reached. It can also cause torque loss. In the case of the S4 V8, it appears, based on evidence from people using downpipes, that the headers do not require significant back pressure. Both the S4 and RS4 engines seem to benefit in the midrange from reduction in exhaust restrictions.