Good point Graham, top end speed and frontal area all things being equal there would for example not be much difference in the CD of my black Mk3 Camaro than your BMW infact I would say the Camaro was slipperier so in that case it would hit the higher speeds than you lighter car but there are not many tracks where you can do speeds like 170mph plus and even then you have to stop the thing so I would say the smaller lighter vehicle would win hands down on the majority of UK circuits which would not be a problem apart form the fact that with this form of classification (power/weight) we may well end up in the same class and the highest capacity class does not always win overall in fact in the ModProds several years ago rarely did.
Also a good point GTPolo, torque is very important for a good lap time, I once built a 400cu engine that had over 400 ft ibs of torque at 2000 rpm (dynoed not make believe
) it was crazy shame it did not live long.