copied from the thread I started on RS246. Chime in with what you know, and correct me if I messed anything up below…
Not looking to discuss which aftermarket catback sounds best, but rather I would like to know what the stock setup is like in order to gauge whether there could be some improvements had by addressing any potential weaknesses.
Interested in the following:
- diameter of downpipes and catback exhaust sections
- is there a crossover (xpipe or hpipe) in the catback section?
- how many catalytic converters are there, and where are they located?
- what is the setup for the manifold…is it a log style manifold, or short headers…or other?
The B7 RS4 had the following setup from the engine back
manifold - tri-y headers
downpipes - 2.5" downpipes that tapered to 2.36" just before it mated up with the catback
catalytic converters - 2 in each downpipes…pre-cat up at the end that mated up with headers and main larger cat down before the mate-up with the catback. Gutting out the pre-cats yielded strong gains for the car while retaining the main cats and their ability to help a car pass sniffer emissions tests. You could also DIY it for free, so this was a great mod. Main cats were very good and flowed well.
catback - no crossover, with a resonated section. 2.36" diameter on the exhaust
As I mentioned above many RS4 owners found gutting the pre-catalytic converters to be a great source for efficiency improvement. The next level of performance gains to be had involved larger diameter exhaust and downpipes. 2.75" was the choice of MTM in EUR and JHM in the US, and we have seen very strong power and performance gains from cars with the 2.75" setups. Other companies went with a repeat of stock size with changes including the relocation of/deletion of catalytic converters or the addition of crossovers or adjusting the flow/shape of the exhaust. These stock sized systems mainly yielded sound gains and modest power gains.