We found in our exhaust development and testing of the 991 GT3 and RS that they are intake limited both through the factory air filter box and through the 82mm Throttle body. A bit of history. The Bosch 82mm Throttle body is the largest Bosch makes and was used as far back as the 996 GT3 which made 380hp. The Air filter box used on the 991.1/.2 GT3 and the 991.1/.2 GT3RS originally showed up on the 2013 991 Carrera S which makes 350hp. Your 991 GT3 is rated at 500hp, so you can see just from these numbers that the intake side of things is a constriction.
In our testing we found the the stock airbox to be about a 0.2-0.3psi pressure loss and the 82mm throttle body to be about 0.3-0.4psi of pressure loss. Naturally aspirated engines make power from the force of the atmosphere pushing air into the engine, so every 0.1 psi helps! Our combo of 93mm Throttle Body and Dual Cone Airbox reduces the losses to under 0.1psi.
