When racing at Maxton, the class you run is based on displacement. I, at present, own E/F CC where 'E' goes from just less to just more than four litres. It's possible to get factory engines as large as a full five litres, but that would put me into 'D' or possibly even 'C'. But one of the factory displacements is right on four litres, so when I went looking for a core from which to work, the engine I got was right on the money.
KS