The Wunderlich exhaust deflector »GONZZOO«
The phenomenon and its cause
During test rides, we were able to identify the resonance chamber, which is roughly formed by the inside of the cases and the entire rear wheel arch, as the source of the noise. The right mounted silencer also protrudes into this space. The resonance chamber turns out to be the sound source because of its geometry, volume and the materials (and their acoustic reflection behavior) that bound it. Accordingly, it is not primarily mechanical vibrations but rather the sound pressure escaping directly from the exhaust that stimulates the described chamber to resonate. This resonance chamber acts like a mechanical amplifier. It is the cause of the droning noise.
After this realization, it was also clear why the noise was particularly noticeable in the partial-load and full-load ranges: these are the operating conditions in which the sound pressure level of the exhaust is physically at its highest.
The aim was therefore to eliminate the resonance chamber described above as the source of the noise. This could only be achieved if the sound pressure and the exhaust gas flow from the silencer were diverted or deflected. We have ruled out a conventional sound insulation - because it was not practicable.
Wunderlich exhaust deflector »GONZZOO«
With this knowledge in mind, our developers considered a deflector solution right from the start. The deflector had to be designed to deflect or shield the sound pressure in a targeted manner so that it would not reach the resonance chamber at all and cause it to drone. This defined the primary requirements of the specifications:
- The redirection of the sound pressure was to ensure significant noise reduction at head height of the rider and passenger.
- The shielding upwards and to the side was to have the additional positive effect that the sound waves are radiated downwards and to the rear and are therefore perceived as less loud.
- In the subjective perception when passing the GS, a significant noise reduction should be achieved - depending on the free field conditions.
- The deflector should shield the heat radiation of the exhaust gas stream in such a way that the heating of the right-hand case and the case contents is noticeably reduced.
In addition to the challenges posed by the demanding primary requirements, our developers paid particular attention to further general conditions. After all, only those who unprofessionally manipulate the exhaust system risk invalidating the operating permit. For this reason, the specifications included further technical requirements of essential importance:
- The exhaust deflector should recieve a type approval certificate (EEC).
- The solution should not affect the engine performance, especially not negatively, i.e. it should not change the backpressure in the exhaust system compared to the series production.
- The solution should be simple and effective, especially when riding with mounted cases.
- The solution should be flexible and small in terms of geometry.
With our now presented exhaust deflector »GONZZOO« we have fulfilled all mentioned requirements. It is model specific designed, to fit the BMW R 1250 GS + Adventure as well as the BMW R 1200 GS LC + Adventure.