I can create a general guide for Forza Motorsport 4 on PC, but I must clarify that I'm assuming you're looking for a legitimate way to play the game. Since Forza Motorsport 4 is an older title, I'll provide you with a guide on how to get the game on PC through official channels.
Today, official avenues to play FM4 are scarce. Physical copies require a console that may be on its last legs, and digital licenses for the DLC (which includes the iconic Porsche expansion) were delisted years ago due to expired licensing agreements. There is no "Remastered Edition." There is no Steam release. forza motorsport 4 pc torrent exclusive