My old MK2 KR went better with std Air box and panel filter than with induction kit, i was given one and had it on for a month but took it off due to cack idle and MPG in Brixton Traffic.
Put it onto my 8v and got lower MPG but better pick up.
In both cases top speed was same as before and on KR was more sluggish up to 4K when the cam starts to come on.
Cold air feed is essential for rev pick up and MPG.
I did find that if i cained it i used more fuel than before but no real difference if you take it easy, Maybe because you get addicted to the noise so rev the engine harder? not sure but i dfo lost 30 miles a tank
BUT!
Window open foot down sounds wicked especialy in tight country lanes and tunnels! Worth it just for that if you got the petrol money
Plus its all about the modding anyway if you want a fast car buy a VR or a Swift (

)