Flow testing the full B5 S4 turboback exhaust system and comparing to the results of testing the Autospeed downpipes and 034 Motorsports 3.5″ single (3″ mid-pipes with dual Magnaflow mufflers) exhaust system.

The setup:

The chrome exhaust tips on the stock exhaust are not airtight, so I needed to tape them up and then wrapped the tape in a rubberized band.

The results:

Conclusions:

A well optimized aftermarket exhaust system can substantially outperform the B5 S4’s stock turboback exhaust system.

Update:

The following chart shows the performance of the stock muffler without downpipes.