As we embark on 2012 we have had insurace changes, USLMRA rule changes and the addition of new classes. Really a tough job keeping up with all the information. Over the summer we adopted a RP class to help bring racers onboard that want to go faster than IMOW but could not afford to build a race engine. USLMRA has adopted the new GP class. Very close to the guidelines, we adopted for the RP class. If you have started to build an RP race machine and want to race the national races, use the USLMRA rules.
G/P: ENGINE: Governed engines, 3650-RPM max (No Load) Single-cylinder Over-Head Valve & Valve in block (“L” Head”) Engines must be Factory stock, complete, and not to exceed a factory rating of 17 horsepower 33ci. After market, consumable parts such as air filters and spark plugs may be used as long as they are a direct stock replacement. Twin cylinders engines and Mid Engine frames are not allowed. 42”minimum unaltered wheelbase, 6” minimum front wheels, 8” minimum rear wheels, and there is no gear ratio restriction.
For more info see our link on rules.
http://www.letsmow.com/wp-content/uploads/2009/03/2012-USLMRA-Rule-Book-Dec-2011.pdf