2. Engine blocks must have an OEM stock appearance and must be factory productions or their OEM replacement with factory deck height. No Woolam or J2 blocks allowed
3. Stock Head bolt pattern, location and size. Stock head gasket must fit over studs or bolts.
4. Maximum crankshaft stroke 3.25" and engine bore 3.780". Maximum 0.010" measuring tolerance, must not exceed 36.5000 cubic inch limit.
5. Maximum engine valve size 1.380 with maximum 0.001" measuring tolerance and maximum engine valve lift .330" with maximum 0.003" measuring tolerance.
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.
7. Carburetor must be a stock appearing Kohler-type and must be mounted to the engine with no more than 1" long spacer. No turbos or pressurized intakes.
8. No reverse port engines allowed, carburetor must go to the original stock intake port.
9. Billet heads permitted with minimum one (1) inch thickness.
10. Porting and polishing allowed
11. No rpm limit but steel flywheels are REQUIRED.
added for 2008
12. No starter-generators allowed. Must use ring gear starter or starter-cart.
13. No external welding except for crankcase area of the block for repair. But no other external modifications allowed.
updated for 2008
14. Engines must run gasoline, E10, E85 only; service station pumped gasoline, no additives. Racing gas and methanol is allowed. Driver must wear full fire suit if tractor is on methanol.
15. Straight pipes and chrome air cleaners allowed.
16. 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.
17. May strengthen drive train to prevent breakage. (Reared, driveshaft, clutch, etc.) Altering gear ratios is allowed.
18. Bar tires and professionally made pulling tires such as Cepeks, Pit Bulls, Lawntecs, etc are allowed. May sharpen bars tires. Adding of bars, such as double cutting, is allowed.
19. Rear tire size: 26 x 12 x 12 maximum.
20. Aluminum wheels are allowed.
21. Clutch covers and flywheel shields are required. Minimum thickness 1/8 inch steel or 3/16 inch aluminum.
22. Driveshafts must have a support bearing in the center or driveshaft loop.
23. Engines must have a scatter shield opposite the cam side of the motor. Minimum thickness 1/8 inch steel or 3/16 inch aluminum. It must cover the full height and width of block and be attached in a secure manner to the frame and head.
24. Engines must have a hold down restraint installed to prevent the cylinder and head from separating from the block.
25. Bumper bars are required. These are a vertical bar at least 6" long mounted on rear most part of wheelie bars. Vertical bumper bar must be even with or behind back face of wheelie wheel or skid.
26. Tractors must have WORKING kill switch fastened to the rear of the tractor in such a way that it does NOT interfere with weights or sled hitching device. The connector must be fitted with a ring with a minimum of 1.5" inside diameter.
27. A minimum 1 1/2 pound dry chemical working fire extinguisher or equivalent. A gauge on the fire extinguisher is required or an inspection and recharge tag not more than two years old. They can either be dry chemical or CO/2-type extinguishers.
28. Tractors must have deadman throttle with return springs on the pedal and the carburetor.
29. Drivers must wear helmets that meet minimum Snell 95 requirements. No football, baseball or toy helmets.
30. Drivers must wear long pants and boots. No sandals or open toes.