only 2 ways to make them faster is loose as much weight as possible (gives you more bhp/ton which is whats most important, and get plenty miles on it.
my old engine on 140k would have murdered my new one with 50k on the clock if i hadn't blown it lol
dont bother wasting money on performance mods just not worth it at all, ive been there done that.
sort out the suspension to make it handle, upgrade the brakes to make it stop, put a stainless exhaust on it so it sounds the part (the 1.2 engines pop like mad with a stainless on them!)