60 cubic inches with a maximum .040 inch over stock. Steel or aluminum rim width will not exceed the tread width of the tire. No tires may be over 26x12.0x12 inches in size. Rim width is not to exceed the width of the tire. Garden tractor type tires.
Stock means a stock motor on a stock frame.
No intake modification. Milled heads are allowed however, see the diagram for specifications. 1 factory type head gasket installed, in the proper location. Camshaft can be any cam grind. Factory stock valve size intake and exhaust valves need to be O.E.M. stock.