Originally Posted by tshih

The new 991 GT3 engine is not based on the 997.2 DFI engine and only share a few fasteners according to AP. Porsche has done the opposite in releasing a street version engine before they raced it in competition. The Mezger engine soldiered on for last year's races because they got some kind of relief with more competitive rules exemption. The current RSR has the same motorsports engine as the 991 GT3 engine and Cup car engine.