Well it was really your comments in the carbon fibre poll thread regarding an aero kit that set me thinking. I had assumed that the marketing hype about the rear diffuser and spoiler etc. was just that - hype. But looking around under the car as I have been for the last few days while it has been up on stands it is obvious that DC has paid quite a bit of attention to airflow underneath. Sure, the diffuser may well be mostly there for aesthetics, but they have taken the trouble to put fairings on the lower suspension arms to smooth the airflow in this area, kept the floor flat and free from protuberances, added a smooth engine under tray and small 'splitters' in front of the front wheels on the front arch liners to isolate the turbulent air around the wheels. Car manufactures don't spend money on fitting bits you can't see if they don't do anything. Admittedly these bits are probably only there in improve high speed stability and counter the lift generated by the cars shape, rather than any generating extra grip but that's not to say they can't be used as the basis of a 'kit' that does! As I see it a proper full width splitter and lower side skirts to completely separate the airflow above and below the car may give some genuine ground effect - its just an educated guess as I am not a professional aerodynamicist!
I have just put my Spider back on the road for summer so I now have the opportunity to have the Crossfire off the road for a week or so and remove the skirts and bumper to take moulds - until now the xfire was my daily driver so I have never really had the time to pursue any of the more ambitious projects I have been dreaming up. Watch this space.

Simon