class updated for 2010, changed to 4250 rpm limit so open rpm safety equipment removed
1. Single cylinder four cycle flathead engines only and must be Kohler, Wisconsin, Tecumseh or Briggs.
2. Engine blocks must be OEM stock factory productions with factory deck height. No reproductions or Woolam or J2 blocks allowed.
3. Stock Head bolt pattern, location and size. Stock head gasket must fit over studs or bolts.
4. Stock stroke only with a maximum 32 cubic inch displacement (allows for .030" overbore of 14 hp block).
5. Engines must use stock lift cams and stock diameter valves.
6. Maximum carburetor venturi size 1.00", no air entering after 1.00" restriction. Venturi must be round in shape. Note, this is referring to the venturi, not the throttle or choke bore.
updated for 2010
7. Carburetor must be OEM carburetors for the models listed in rule #1 with no spacers allowed. No carb body inserts allowed. No recast carbs allowed. No turbos or pressurized intakes.
8. No reverse port engines allowed, carburetor must go to the original stock intake port.
9. Stock or stock appearing heads required. No Billet heads allowed.
10. Porting and polishing allowed
11. No external welding except for crankcase area of the block for repair. But no other external modifications allowed.
class updated for 2010
12. Engine RPM must be governor controlled. Maximum rpm limit 4,250 rpm. No tolerance allowed.
13. Engines must run gasoline, E10, E85 only; service station pumped gasoline, no additives. Racing gas is allowed.
14. Straight pipes and chrome air cleaners allowed.
15. Must run a factory appearing hood and grill, use garden tractor rear-ends and stock garden tractor frames that are factory length with a maximum wheelbase length of 52 inches.
16. May strengthen drive train to prevent breakage. (Reared, driveshaft, clutch, etc.) Altering gear ratios is allowed.
17. Bar tires are allowed; but no professionally made pulling tires such as Cepeks, Pit Bulls, Lawntecs, etc. Tires must be ag type bars. No double cutting of tires, no adding bars, but can single cut the bars in any fashion. No cut turf tires allowed.
18. Rear tire size: 26 x 12 x 12 maximum.
19. Aluminum wheels are allowed.
20. Clutch covers and flywheel shields are required. Minimum thickness 1/8 inch steel or 3/16 inch aluminum.