You may have noticed that we’ve discontinued our 991.1 Carrera Valved Exhaust and a new system is available in its place. We’d like to share the development process behind our new and improved Valved Performance Exhaust system!
Resonators can reduce annoying drone and provide a smoother exhaust note without sacrificing volume and aggression. While the resonators we used were effective – we wanted to keep the aggression of the exhaust but refine it to have even less drone and in cabin intrusion. Effectively, our aim was to refine the level of daily driving comfort without sacrificing the race inspired tone and straight-through exhaust design. A larger resonator would not yield the results we are looking for while requiring some revisions for clearances – this could compromise the high flow design principles of our exhaust. Another thing to consider is that adding higher flowing aftermarket headers – like our Long Tube Street Headers – to an aggressive rear system without proper sound attenuating features could result in a overly loud, possibly unpleasant driving experience. Nearly 40% of our customers paired their rear exhaust with upgraded headers making it imperative that we consider such a configuration and engineer the exhaust appropriately. We set out to experiment with both factory and aftermarket headers to find the perfect recipe.
Helmholtz resonators (also known as anti-drone tubes) are an effective way to reduce undesirable frequencies when engineered and utilized correctly. We have years of experience incorporating them into our exhaust systems, such as our 996-997 Turbo Competition Exhausts (pictured below) to cut down on the in-cabin presence that is well known to arise in these vehicles with modified exhausts.
Through calculations on factors such as number of cylinders, target RPM, and other factors (Sorry – SOUL Secret Recipe 😉 ) you can determine the appropriate volume necessary to create the Helmholtz resonator. The 991.1 Carrera has an inherent 3,000-3,500 RPM range where drone can present itself when you add higher flowing exhaust components. Our goal was to filter out the undesirable frequencies in that range while smoothing the valves closed to open transition on factory PSE equipped cars.
Back to the R&D table. We had fixtured a stock center muffler to define the area in which we can work, mounting points, and any design restrictions. With our calculations in place, it was time to craft a system and start experimenting with the Helmholtz resonators to get the sound we are looking for.
We began work on the first version of our design. Each system is TIG welded together in a heavy gauge aluminum fixture. Why aluminum? Although it’s more expensive it prevents any potential warping over the life of the fixture – steel can warp over time causing possible fitment issues in the future. This ensures our products fit perfectly every time.
We completed the prototype system and mounted it to the vehicle – with and without our catted headers. The exhaust sound was improved and drone mitigated to a noticeable extent – but where some may stop and call it a success, we wanted to do further testing to get the best possible results for our customers. Slight changes were made for Prototype 2 to test the effectiveness of not only the calculations, but the placement of the tubes themselves.
While we were installing the second prototype – we noticed the inner shell on the primary exhaust tip is held on by three small spot welds. Removing this inner tip section effectively increases the inner tip diameter from 1.5″ to 2.5″ to match the 2.5″ outlets of our exhaust perfectly for maximum flow! You simply grind down three small spot welds and the inner shell comes right out.
We highly recommend this modification when using your factory tips with our Valved Performance Exhaust for the greatest efficiency, we’ll even do it for you! Alternatively we will be offering both polished chrome and black chrome tips to achieve the same effect.
For the final prototype we relocated the anti-drone tubes to the exhaust inlets, right off the main pipes instead of the T’ed off design shown above. This design has proved to offer the very best results on this application and achieved our high standards for sound quality and drivability. The math can be done to create the Helmholtz resonators – but how you incorporate them into your design makes a big difference.
The sound is aggressive – a primary benefit of our system is that with valves open there is straight, unrestricted path from the 2.5″ piping to the tips – but we’ve effectively massaged extra refinement into the system to match the premium experience that embodies all things Porsche. With valves both open and closed the X-pipe helps smooth the sound even further. All in all, we’re very happy with the results and we’re sure you will be too!
Now it’s time to wrap up development and start production.
Mandrel bent piping is cut to fit into cast templates – you can see us working on a template here. This allows the fabricator to “kit” the pieces necessary prior to welding.
Here is Max building a system for our first production run. Back purged welds ensure proper penetration and exhaust longevity.
Our proprietary blasted finish not only looks great but reveals any imperfections such as pinholes in welds that are normally hard to detect on raw or polished stainless steel. This along with our back purged welds results in the best possible product and longevity. It also allows us to refinish at any time should you want your exhaust parts freshened up.
Before each system ships we do a final inspection for fit and finish then securely pack it up with hardware, installation guide, and a microfiber towel to wipe any debris off from installation. Expanding foam ensures even coverage all around each component to prevent any potential for damage in shipping. It’s time consuming and expensive, but our mission is to have a perfect product in your hands every time!
Thank you for reading our development post! We’d be happy to answer any questions that you have or point you to your nearest SOUL dealer and installer for a system of your own!
Questions? Comments? Let us know!
– Mike Spock / Marketing Manager