If you encounter files labeled as "Forza Motorsport 4 PSP ISO" or "PPSSPP Mods," these are typically: Total Conversion Mods
As for Forza Motorsport 4, if you're interested in playing it, you'll need an Xbox 360 console or an Xbox One console with backwards compatibility, as it's not available on PSP or other platforms.
Fans often take the game Gran Turismo (PSP) and replace the car textures, menus, and music to look like Forza.
If you see a YouTube video claiming to show Forza 4 running on a PSP:
If you encounter files labeled as "Forza Motorsport 4 PSP ISO" or "PPSSPP Mods," these are typically: Total Conversion Mods
As for Forza Motorsport 4, if you're interested in playing it, you'll need an Xbox 360 console or an Xbox One console with backwards compatibility, as it's not available on PSP or other platforms.
Fans often take the game Gran Turismo (PSP) and replace the car textures, menus, and music to look like Forza.
If you see a YouTube video claiming to show Forza 4 running on a PSP: