all the bolt on mods work together very well when you have added them all, each one makes a noticeable improvement, and when you have them all it will sound better (not just louder) breath better, better MPG, better torque and around 160-170bhp, it will be sharper and smoother too, go for a quieter resonated system otherwise do some soundproofing to bonnet and boot. Can highly reccommend the Ford Bonnett Soundproofer -best £60 ever spent seeing it does not come with one from factory.