nah, hayabusa engines will easily get 400bhp from a single turbo, check this out...
http://www.zcars.org.uk/mini/specifications.htm
"Hyabusa Turbo Suzuki with ½ tank of fuel, all steel bodyshell, boot bonnet trimmed for road use and ready to drive:
Weight 650 kilos
0 to 60mph 3.4 seconds
Standing quartermile 11.0 seconds 130 mph
BHP at Crank 400
Power to weight ratio 615bhp/tonne
This can be self built from £18000"
Costs "£18000" when they do everything for you, you can cut this down alot depending on your abilities and facilities.
Ive seen a few vids of Hayabusa/R1 minis, some from their site,
Check
THIS one out :thumb:
Quite a few pics and stories of people who also built bike engined minis
here.