Chris - as you know my new class 5 engine was down on power from what was expected. I am investigating every option. Talking to Steve at Track and Road, airboxes can have a major effect, expecially with cams that have a large overlap. It is usually pulse interference effects and the big car manufacturers spend millions on developing the right length inlet tracts to eliminate these effects. Just ask any Duratec R500 owner what effect the "quiet" airbox has on power! My plan is, as you guessed, to have a swappable system, mainly so I can prove on the rolling road if the airbox is a problem or not. If it is then I will continue with the swappable system, if not I'll just leave the airbox on. Anyway my existing airbox is very close to the 90mm trumpets so I would like to use one that sits further away - I was looking at your airbox at Gurston and it looked to be nearer the outside of the car so would hopefully give more clearance. If I can find my missing 20 horses I will be a happy man.