There can only be two valves per cylinder. The heads are machined from aluminum billet and have no water jackets, as the high latent heat of the methanol in the fuel coupled with the brevity of the run precludes the need. Superchargers are restricted to a basic Roots type and only single camshafts are allowed. The 3/4 stroker is the most common combination used today and equals 496 CID (8.1 L)