This looks quite interesting.
http://www.pistonheads.com/news/default.asp?storyId=29075
Ive just written to them to see what costs and options are for getting this fitted to my wives MX5!
A few weeks ago I was taken as a passenger around Donington:
Roddison Motorsport MX5 race car with the BBR Stage 3 Turbo and forged engine, 335bhp. Needless to say on a cold and damp November track, much of the lap was very sideways. Nothing went past it all day, although Paul Roddison does drive like a lunatic
If you are looking at costs then speak to Paul Roddison as well as BBR, he can supply and fit the kits too - based in Sheffield, nice guy to deal with. I'd love the turbo kit but I feel the final price is somewhat high, higher than most who want a turbo Mk3 would be willing to pay.
Myself, I am due to finish my MX5 Mk3 engine mods on 31st January. AEM intake (fitted), Milltek cat back with sports cat (fitted), next up is a Racing Beat manifold and Ecutek remap, should see me to 180-185bhp with a much more fitting soundtrack for a sports car, this is an equivalent set of mods to BBRs own 'Super 180' or Roddisons 'RMS185' packages.
The biggest changes come with drivability rather than outright power, the original throttle maps are very conservative for the 3 lowest gears, this is to save the traction control from kicking in but also provide a greater level of 'safety'. The map removes these so the whole car feels much more urgent, quicker to give you its power, as well as the 20-25 gain in peak bhp and torque.