Where once we used to develop an exhaust primarily for improving performance, we are now increasingly looking at ways of enhancing the character of the exhaust note. The latest 718 Porsche GTS & GT4 models are a prime example of a stunning engine that loses much of its character and excitement through its’ muted exhaust. In models that are as dynamically impressive as the GTS & GT4 the drama from the engine should match the ability of the chassis.
We received our own Porsche GT4 for development the week before we went into lockdown back in March 2020. So, this gave us plenty of time to get to know the car in standard form and decide upon what upgrades we would make. The latest GT4, like the new GTS, features an all new 4 litre normally aspirated engine. However, it also has to run large particulate filters to compile with the latest European emission standard. These dense exhaust filters stifle both the exhaust flow and most importantly the sound waves coming from the engine.
It became clear that the exhaust was the first port of call for our upgrades. As the GTS & GT4 are such new models we believed that most customers would be looking for a catalytic converter back exhaust system that wouldn’t impinge on their factory warranty. The primary goals were to produce a characterful and measured engine noise, reduced weight, increased performance and all at a sensible price.
We would utilise dual OE grade exhaust valves to control the sound via both the engine ECU and the Sports Exhaust override button within the cabin.
We produced four main designs for an improved exhaust system which were expertly fabricated here in the UK. Included was an extreme example that features a blown rear diffuser where we bought an additional central diffuser to modify to see what the sound and performance will be like.
Initial testing on our Maha Dyno show that all designs would provide a significant power increase when the exhaust valve is open thanks to its free flowing path. Our dyno testing showed a 20 bhp improvement over stock with just a change to the rear silencer and useable gains in to torque from as little as 4,000rpm (14.5lbft @5,000rpm) with power is also increasing higher up the rev range where the engine spins more freely as it accelerated to the redline. However each of the exhaust designs had a mark change in exhaust note and sound level both in and out of the cabin.
With Lock down measures eased we were able to get back out on the road and do more subjective testing. Here it became obvious why the factory had to use such a substantial rear silencing system as the mid-engine layout made the car very susceptible to droning when cruising. During our design process our Engineering team of Jim and Scott worked closely with our exhaust company to produce multiple different silencer configurations and designs which utilised Holtz resonators to remove this unwanted drone. We have designed the new systems to retain the standard tail trims which both look great, retain the OE appearance and reduce the cost of the system. The weight has been reduced by 7kg compared to the OE system. Eventually we settled upon two systems that sounded superb on the road but we also wanted to double check them on track.
The final development stage saw us hire Castle Combe race circuit where we could test the noise volumes for both drive-by and cabin sound under sustained load and high-speed speed. With so many GTS and GT4 customers using their vehicles on track it was important that they would stay within circuit limits without reducing the excitement that a good engine note should provide.
Accompanied by Motoring Journalists and TV presenter Paul Cowland we set about signing off our final design by swapping between the standard system and our revised exhaust while trackside.
Watch the video below for Paul’s thoughts on both systems.
Our Litchfield exhaust system is now available to order for your 981 GTS and GT4.