Bought a K&N induction kit for £10 today from Halfords. Not for a 172, but it looked like itd fit, so I gave it a go. Went on okay, so took the car out for some AP22 testing. On the same bit of road, the car was 0.5 slower to 60mph and 1.5 seconds slower to 100mph. Ah well, just goes to show that the hot air theory isnt just, erm, hot air.
Rhys