AMERICAN
BIG BLOCK MODIFIED RAILS
9-2-2023 in effect till 2027
Updated 3-25-2023
Verification of Rule 5 – L 10-14-23
1. Weight
a. 5500
2. Driver
a. 16 years or older
3. Tires
a. whether U.S. or metric numbering system - can be no larger than 18.4 X 38
b. any cut
c. rear rims must be steel
d. bias or radial
e. no duals
f. no out of mold double cut tires allowed
4. Fuel
a. commercial pump gas
b. race gas
c. aviation fuel
d. no alcohol
e. no nitrous oxide
f. no pressurized fuel tank
5. Engine
a. American made big blocks
b. 500 cubic inches or less
c. must be cast iron block, heads, and single two barrel or four barrel cast iron intake manifold – with visible factory casting numbers – all must be same manufacturer
d. 2 valves per cylinder
e. 1 sparkplug per cylinder
f. no overhead cams
g. must be naturally aspirated on carburetion
h. headers must exhaust in upward direction
i. flat tappet or roller lifter camshaft
j. stamped steel rockers or roller rockers allowed – stud or shaft mounted – must be factory ratio or smaller than stock ratio for the motor - laser etched or tech checked to be approved - tech officials may pull valve cover at any time
k. all tractors must use a Holly model 4777 carburetor – No modification to carburetor except for tuning. Tuning includes accelerator pumps, jets, power valves, and sight glass fuel bowls. Choke plate can be removed but the choke airhorn must remain intact. Spacer plate, if needed between carburetor and intake 1 inch maximum thickness
l. all tractors must run club supplied restrictor plate. Plate must be installed so as ABBMR logo and the plate numbers are visible. No modification to this plate will be allowed TO THE BORE – Plates may be inspected at any time by club officials. Any plate found to be bore altered will result in immediate disqualification for remainder of the season.
m. distributors – Any factory or after market distributor O. E.M
n. ignition - M.S.D. #6AL-6420 or #6ALN-6430 – rev limiter box with 6000 chip - Tech committee will check RPM’s with a 2500 chip at pulls, also 6000 chips may be randomly traded by tech committee at each pull.
o. crank triggers or any other type of electronic spark trigger not contained within the O.E.M. distributor will not be permitted
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6. Tractor
a. 2 wheel drive farm type tractors only – with original transmission housing attached to the rear end – must have at least one forward and one reverse operable gear – no planetaries – no extra transmission or gearing of any kind outside of the tractor’s transmission housing other than the automatic transmission on the engine - Tractor gearing can be changed
b. maximum length 14’ from center of rear axel to furthest point forward including weights
c. must have wide front end – Front tires must track inside rear wheel tread
d. must have working brakes
7. Hitch
a. 20” maximum height
b. hitch point 18” minimum behind centerline of rear axel – the distance behind hitch hole may not exceed more than 1 1/2 “
c. must be rigid in all directions
d. minimum opening 3 ½”
e. minimum 1” thick maximum 1 ¼”
f. turn buckles or hitch adjustor cannot be higher than the center of the rear axle
g. no obstruction 5” wide and 24” directly above hitch hole
8. Wheelie Bars
a. must support weight of tractor in its heaviest class
b. must extend a minimum of 32” behind the center of the rear axel
c. pads must be a minimum of 5” inches square with trimmed corners optional and not more than 10” off the ground
d. wheelie bars are to be mounted separate from hitch
9. Miscellaneous
a. there will be a required driver safety enclosure made from a minimum of 2” tubing or larger, – enclosure will not be approved until strength tested by having a loader tractor tie on to the top of the enclosure and pulled sideways to lift rear tire off the ground – refer to attached diagram for minimum building specifications – Tubing must be steel and a minimum of ninety thousandth l of a inch wall thickness. The ultimate responsibility of safety of the roll cage lies with the driver/owner.
b. deadman throttle required – spring at carburetor return to idle c. ignition kill switch required – must stop fuel pump and ignition – must be
mounted above hitch plate – must run electric fuel pump – easily
accessible and visible to hitchman on boat
d. electric fan required - absolutely no fan blades on engine
e. fire extinguisher - mounted within driver’s reach – must be readily
accessible and a minimum of two pounds
f. all belts must be 360 degree shrouded with 1/16” steel or 1/8” or thicker aluminum
- Harmonic balancer (SFI preferred) must be surrounded 360 degrees by a
min. 3/16” thick steel – also a metal strap over the center of the balancer . must be a min. of 3/16” thick and 3” wide, with a max. 1 1/8” hole for
access to the crank center bolt. Max. ½” hole is allowed at the
timing indicator marks to allow for engine tuning. Entire enclosure must
mounted in at least 3 solid points.
g. universal joints, chain couplers and/or drive shaft must be surrounded 360
degree by ¼” or thicker steel (entire shaft length) Round drive shaft cylinder required
h. automatic transmission must be surrounded by a SFI 4.1 or 4.2 rated transmission blanket at least 18” in length. Blanket must be mounted to the block with no more than a 4” gap between the block and the blanket and have at least 3 straps encompassing the transmission. ¼ steel may be used instead with same dimensions applying.
i. automatic transmission must have park and neutral start safety switch
j. everyone must run an automatic transmission with a torque
converter - mounted directly to the back of the engine
k. side shields – must be made from 1/8” or thicker steel or ¼” or thicker aluminum – must cover from front to rear of block and cover from the bottom of the head to 2” below crankshaft center line – must be secured at all four corners
l. tractors are to be driven on all occasions – the only exceptions are pull offs
or mechanical breakage
m. a catch can of at least 28 ounces installed or volume according to need to
to prevent liquid from spilling onto pulling track.
10. Driver Safety Equipment
a. single layer fireproof driving suit
b. helmet – D.O.T. approved
c. high back molded vinyl, fiberglass or aluminum race seat
d. minimum 4/5-way safety & restraint harness
e. neck brace
f. automatic shifter activated reverse clear lens back up light – with unobstructed view to hitchman on the boat
g. all non-barbed fittings (cooling or fuel)must be double clamped