Originally Posted by Andrew@IND
Akrapovic is a great option, however, if you are looking for the loudest option it may not be the best choice. Akrapovic is known for a quality that is quite simply second to none. The only concern is that it does not have the same presence as a say a race performance exhaust. This is primarily due to TÜV homologation and the strict requirements the said governing body has on exhaust manufacturers.
Have you checked out Eisenmann?
Eisenmann is another option out there that you might be interested in. As an OEM manufacturer for both Porsche and AMG, Eisenmann has access to a plethora of TUV approved testing equipment, including frequency analasys equipment, enabling Eisenmann engineers to design a system that produces a loud exhaust volume while also maintaining a focus on the appropriate M5 tone.
While it's true that in many cases it's TÜV that is responsible for the testing of equipment etc to confirm compliance with standards, TÜV is NOT a governing body. They are a independent laboratory/technical service that does several varieties of compliance testing in many areas.
There are today 4 different TÜV companies based in Germany, TÜV Süd, TÜV Nord, TÜV Rheinland and TÜV Saarland.
Today companies like DEKRA also offer the same services as TÜV.
The German governing body for cars are the KBA (Kraftfahrt BundesAmt - Federal Motor Transport Authority). 99% of auto related legislation is issued by the EC and implemented in national legislation throughout Europe, giving a harmonized legislation in many areas.