Using commonsense about 120/150 hp,180 hp maximum,if you want to use higher power use 32x32 x1.6 or larger.Take a look at the Brunton 7 Stalker USA.These space frames are not as strong as everyone thinks,in fact a simple ladder chassis as used in typical US rods is stronger and once cross braced much stronger.Also 120 hp will easily do 0 to100 in under 6 seconds.I believe the limitations of clubman 7 cars is the old fashioned diff (sprung/unsprung weight)but the independent rear suspension of the Haynes Roadster will lift the clubman 7 roadholding to a new level.
David