We are thrilled to get started on exhaust development for the new 992 GT3! Let’s dive right into what’s going on in this car. More photos and videos will be forthcoming as we progress with development.
EXHAUST LAYOUT SUMMARY
The new GT3 as shown here now has two modular exhaust sections compared to the previous 997 and 991 generations that had three. Starting at the front, we have the headers and primary cat assemblies. The exhaust then bolts to a massive single muffler assembly which houses the exhaust valves. These valves are now electronically actuated instead of vacuum actuated.
The factory headers are now an assembly with the cats and newly added particulate filters, weighing in at 31.1lbs for the pair. Some of the immediate low hanging fruit that pops out are shorter primary tubes into a rather short hydroformed merge collector. The rest of the header is taken up by large and dense catalytic converters, which then proceeds into equally restrictive particulate filters. Only the cat sections are monitored by O2 sensors, which means there is a potential for performance improvement in deleting the particulate filters in a header design utilizing higher flow cats that scrub enough to reduce the chance of a CEL coming on. The exhaust then exits the headers and into the muffler assembly via a connection point with a massive 7 ⅝” diameter flange. This is a notable restriction point as the design of the exhaust goes from 7 ⅝” into a shallow bowl in the factory muffler. This means a complete system replacement with an optimized merge collector using a longer and smoother diameter reduction is another option for performance improvement. We will be making Competition Headers that eliminate this massive flange and concentrate on maximizing the runner length and merge collector into a full 3” race system in a catless and high flow catted configuration. This will offer the most weight loss and sound gain possible as we want the option for something that screams pure unadulterated RSR race car! We also plan on making a set of high flow catted headers that are modular to the factory rear muffler system while eliminating the unmonitored GPFs. This is ideal for those that want to maximize the potential of the factory muffler system. With the superb new rear aero improvements, clearances are TIGHT from the headers to the underbody panel, so we may have to get creative with R&D in this section.
Porsche has been using the same side mufflers and center muffler on the GT3 platform for the 997.1, 997.2, 991.1, and 991.2 with negligible changes save for tip assembly size and length – that’s over 15 years! For those that don’t want to opt for the full system replacement (our Race Exhaust System) with either catted or catless headers we have plans for the muffler section to kick things up as well.
Let’s talk about this massive and complex factory PSE muffler. It weighs in at 37.2lbs with the tip assemblies, and with valves closed it significantly cuts down on sound and resonant frequencies through the muffler body via a 1.75” flowpath and six perforated walled chambers. With valves open it essentially bypasses the entire muffler assembly through a 2.5” entry that expands to approximately 3” internally on the muffler before necking down again at the tip connection to 2.75” where it exits the muffler.
If you’re looking to stay emissions compliant in more restrictive areas like California and Europe, the muffler is a logical choice to start with an upgrade. We intend on offering several different versions of muffler replacements on this car – a non valved, wild, and cost effective option for those that want to drop as much weight as they can with the most aggressive sound. We’re also building a valved system to have a similar wild factor with valves open but with a more comfortable cabin presence in the 2k-3k rpm range and the ability to close the valves and fly under the radar. The space constraints with the diffuser will make this even more complicated than the header development, but we’re up for the challenge and will start playing with the rear exhaust configurations once we overcome the most complicated part of the development…designing and implementing a smooth and efficient diameter reduction off the 7 ⅝” header flange. We are well on our way with 3D printed prototypes and networking with a number of companies that specialize in hydroforming these types of shapes for exhaust systems.
European sound restrictions have been getting more and more strict over the last decade or so. Every time a new car is released from Porsche, the PSE programming becomes more and more invasive in controlling the sound level of the car. On previous gen Porsches with the PSE button pushed the programming will override what you want and close the valves until you reach a higher rpm range. The 992 GT3 is no different, and in fact it’s now worse. Now more than ever the most inexpensive mod on sound you can perform on a GT car is eliminating the factory valves and/or overriding the valve control. It’s much more complicated now in this platform because the valves are no longer vacuum actuated and simply 100% open / closed – they are now electronically actuated. Even with the PSE button pressed the valves don’t start opening gradually until right around 4k rpm on heavy throttle input. The valves then follow the rpms at that point slowly opening, and it’s not until about 5k rpm that the valves fully open…
This leaves any valved exhaust system with low hanging fruit to fully tap into the sound potential in the low end and mid range of the power curve. The challenging part now is that if you try to unplug the valves to stop them from closing, the car will set a CEL and not allow the car to rev over 6k rpm. If you remove the electronic valve actuators from the system you cannot use the existing valved exhaust you took the actuators off of as they hold the tension on the valves themselves and they would simply flap around at that point. That all said there are a few ways to upgrade the sound experience on this car around these new electronic valves, which you’ll find available from us in the near future:
- Valved exhaust options that retain the use of the electronic valve actuators.
- ECU tuning to have the valves stay open right away and fully once the PSE is turned on.
- Non valved exhaust options with separately mounted valve simulators for the existing electronic valve actuators.
- Using separately mounted valve simulators and a bolt-on retainer to hold the existing factory or aftermarket valves in the exhaust in the valves open mode without valve rattle.
Stay tuned as we continue development and release our suite of exhaust components!
Questions? Comments? Let us know!
Mike Spock | Marketing Manager | John Gaydos | Performance Specialist