Technical specifications of engines

[ocZio]

Hi, a bit a geeky question here... what are the differences if any between these engines? I have tried to find online but most of the information is around marketing and the overall changes of the car (weight/downforce etc..) rather than the engine differences itself. Thanks.

991.1 GT3RS
991.2 GT3
991.2 GT3 RS
992 GT3
991 Speedster
991 R