Engines must be derived from non-competition motorcycles but the scope for modifications is very open past that. The class capacities are:
- 2 stroke 55-100cc (Under 70cc is allowed forced induction)
- 2 stroke 55-125cc air cooled (Over 104cc restricted to a 20mm Carb)
- 4 stroke 55-150cc (Under 100cc is allowed forced induction)
- 2 stroke 0-50cc
- 4 stroke 0-100cc air cooled (Over 53cc restricted to a 20mm Carb)
There is some further scope for re-bores in the rules.