Basics are a performance panel filter (induction kits suck in too much hot air on the mk3) and an exhaust. If you want to go further than that then you're looking at a stainless manifold. Next steps up would be head polished and ported, fast cams. A step further is having it supercharged for around £1500 all in. If you want more than that then there's the turbo route. If you want to take it stupidly further then it's bored out block and oversize pistons with lightweight pulleys, lighetened and balanced flywheel etc etc
