Jo, I'm rather surprised by your remark - "I can think of many people who were cheating (not just top 3 finishers)". Wouldn't a fairly simply answer here be to dyno the bikes. As peak torque represents maximum airflow efficiency of an engine, a good dyno guy should be able to tell more or less at a glance if an engine was significantly oversize? If the torque was substantially up, the capacity would be suspect. BHP is torque x revs so it's relatively easy to figure out how far oversize an engine is at any particular engine speed compared to a known legal motor...