LIMITED MODIFIED RULES
download or printing - Limited Modified Rules
- Rules apply at all times car is on track. Snell-rated SA2000, SA2005, or SA2010 helmet required. Roll bar padding required in driver compartment (Fire retardant recommended). SFI-approved full fire suit required. Fire retardant gloves, shoes and neck brace (or head and neck restraint) required.
- Right and left seat head supports required if using head restraint system with no neck collar. Recommended: Fire retardant head sock and underwear.
- Driver-side window net required, minimum 16 inch by 20 inch ribbon or mesh style, and must be mounted to roll cage so latch is at top front of window.
- Minimum three inch (two-inch with head restraint system) wide SFI-approved five point safety belt assembly required (Y-type shoulder harness not allowed), must be mounted securely to roll cage, and must be no more than three years old. Kill switch required within easy reach of driver and must be clearly marked “OFF” and “ON”.
- It is recommended that each racecar have built-in fire extinguishing equipment, but cannot be of the dry powder type (must be Halon 1211 or equivalent).
- Drivers should have in their pit area as part of their equipment, at all times, a fully charged dry chemical, Halon (or its equivalent) fire extinguisher. Ten (10) or thirteen (13) pound fire extinguishers are highly recommended.
- OPTION 1 - (southern sportmod or hot mod chassis) 1978-1987 OEM mid-size metric frame a) Wheelbase must be a minimum 107” and maximum 109”.
b) Frame may not be altered anywhere by any means except for the following:
c) Front upper control arm brackets may be relocated
d) Frame may be notched for radiator clearance
e) Frame may be notched for seat clearance
f) Transmission crossmember mounts may be removed no further forward than factory mounts
g) Rear of frame behind upper shock mounts may be replaced with round, square, or rectangular tubing.
h) Frame horns may be removed in front of steering box.
i) Weight jacks are not allowed.
j) Frame must not be lower than 5” from level ground except for front crossmember.
OPTION 2 - (B-mod chassis)
Any 1960 or newer parallel American passenger car frame
a) Wheelbase must be a minimum 108” and maximum 112”
b) Frame must be complete except rear of frame may be cut at a point no further than 36” from the center of the rear end.
c) Frame may only be altered for installation of springs and shocks.
d) Frame may be notched for radiator clearance
e) Frame may not be narrowed or widened and must support the cage on both sides.
f) Must have a minimum 4” ground clearance and weigh 2500 lbs.
- All frame bolt holes must be in original location.
- Tubular front clips are not allowed.
- Jeep, Bronco, or similar four wheel drive frames are not allowed. Front wheel drive frames are not allowed.
- Must have a 360 degree driveshaft loop no more than 6” behind the front u-joint. Must be minimum 0.250” x 2 “ steel strap or 1” tubing.
- Round steel tubing minimum 1.5” x 0.090” required for the main cage. No soft materials. Cage must be properly welded, must be accepted by Southern Oklahoma Speedway officials. Installation and workmanship must also be accepted by Southern Oklahoma Speedway officials.
- Roll bars within the drivers reach must be padded with an accepted material, preferably fire retardant.
- Cage must be mounted to the frame in at least 6 places.
- Cage must consist of front and rear bent hoops connected by tubing on the sides or side hoops.
- With driver securely belted in the driver seat with full gear, driver’s head must not protrude above the bottom of the roll over bar or hoop.
- Must have a minimum of 3 windshield bars in front of the driver.
- Braces forward of the roll cage must not be higher than the hood.
- A minimum of 3 driver side door bars must be parallel to the ground and located perpendicular to the driver so as to provide maximum protection for the driver. Side bars must be welded to the front of the rear of the roll cage members. A minimum 1.5” x 0.083” steel tubing required for all door bars. Driver side door bars are required to have at least 2 uprights not counting the roll over bars.
- A steel door plate minimum 18 gauge or 0.049” thick must be installed and visible for inspection. Plate must be even with front and rear of driver seat.
- Passenger side must have a minimum of two door bars with at least 1 brace horizontal or angled.
- All three link cars must follow cage guidelines as stated in USRA modified rules.
- No composite body panels except for hood scoop and roof rock guard.
- Body must remain the same width front to rear and must be within 1” parallel to the OEM frame.
- Nose piece may have maximum 2.5” side fins on aluminum nose, no scoops, cooling holes are permitted. Nose piece must be no wider than 2” of the factory frame horns. Nose piece must remain inside the front bumper. May be aluminum or MD3 pn 020-410.
- Original roof line must be retained with a maximum 5” rake front to rear.
- No panels are allowed on either side of the engine compartment.
- Excluding hood and nosepiece the body may extend no further forward than 6” of the rear of the engine block.
- Hood must be level or rake down toward the front. Reverse hood rake is not allowed. Rear of hood must be enclosed.
- Panels from the passenger door to the engine compartment are not allowed. No inner panels.
- Front and rear roof supports are mandatory.
- Side windows must have an opening at least 12” wide and 12” tall and large enough for the driver to get in and out easily.
- Roof must be aluminum or fiberglass. Dished roofs are not allowed. Driver roof hatch is permitted.
- Maximum 1.5” rock guard is allowed at the front of the roof. Maximum 4” wide “A” pillars allowed. Maximum 1” raised ridge allowed on the sides of the roof and must run front to rear only, no side to side. Maximum 1” rear roof stiffener allowed and must point down.
- Sail panels must be matching shape side to side, must not extend forward of the rear of the driver seat. A maximum of 4” bow allowed on the sail panels.
- Rear deck lid and trunk area must be covered.
- Overall width of the racecar must not exceed 78”. Width shall be measured at the widest points of the race car. Body panels may not be wider than the tires.
- Rear spoiler is permitted but not mandatory
a) may be a minimum 1” tall or (maximum 8” tall for southern sportmod or hot modified chassis and maximum 5” for B-mod chassis) and must not exceed 67” wide.
b) may have stiffener but must be minimum 1” below the top of the spoiler.
c) a maximum of 3 spoiler braces are allowed and must be mounted parallel to the sides of the body. Braces cannot be more than 1” taller than the spoiler.
d) spoiler must not extend beyond the outside spoiler braces.
e) fins, lips, and wings are not allowed
a) both front and rear bumpers required. Must not have any sharp edges. Front bumper must be mounted frame end to frame end and bottom loop must be parallel to the ground.
b) bumpers must be a minimum 1.25” and maximum 1.75” round or square tubing with a minimum 0.090” minimum and 0.125” maximum thickness.
c) rear bumpers may not extend beyond the outside the width of the rear tires. May extend a maximum 2” wider than the body and must be capped. If the rear bumper extends beyond the body panels it must wrap around and connect to the rear rub rails.
d) Bumpers must be a minimum 16” and maximum 20” from the ground.
e) Rear bumper must not be more than 6” behind the rear of the quarter panels.
f) Single bar rub rails are allowed on each side from front to rear tires and behind the rear tires to the back bumper. No center supports are allowed. Maximum 1.25” x 0.095” allowed and must mount to the cage or frame at the front and rear of the rub rail.
a) all racecars must be numbered with large legible numbers on both sides, on the roof, the nosepiece, and on the right side of the rear valance panel. Numbers should be contrasting in color to the rest of the car. Side numbers must be a minimum 4” width and 18” tall. Top numbers must be a minimum 4” wide and 24” tall. Nose piece and rear valance numbers must be a minimum 1” wide and 4” tall.
b) Officials reserve the right to approve or disapprove any image of lettering or sponsorship on any racecar or pit vehicle entering race surface. Keep in mind this is intended to be a family fun facility.
a) must have a minimum 3 windshield bars in front of the driver
b) Lexan or aluminum panel in front of the driver must not be wider than the cockpit and must not extend rear of the steering wheel.
c) Floor pan must be metal or aluminum and must cover the complete cockpit.
d) Bottom of the seat must not be lower than the bottom of the frame rail at any point.
e) Driver must be sealed off from the track, driveline, engine, fuel cell, canisters, and pumps.
f) Driver must not be within reach of anything that can alter wheelbase or vehicle height while in competition.
g) Rear view mirror devices of any kind are not allowed.
h) Loose objects and/or ballasts are not allowed in the cockpit.
i) Air bags are not allowed
j) Factory-manufactured high back racing seats are mandatory, and must be acceptable to officials. Homemade aluminum, plastic or fiberglass seats are not allowed. Full containment seats are recommended.
- One 12 volt battery allowed. Must be sufficiently protected and securely mounted.
- Battery must have non-conductive rubber or plastic over battery posts.
- One starter OEM or aftermarket allowed. Must be mounted in OEM position/location.
- Vehicle must be capable of leaving the staging area on demand, under it’s own power, unaided or go to the rear of the race.
- No unapproved cameras, transmitting, recording, or transmitting devices allowed in the driver compartment; exceptions are one-way RACE-ciever and analog recall tach.
- One OEM HEI distributor or factory style distributor only. Ford/Mopar may use HEI distributor (Ford and Mopar may use factory unaltered external spark control boxes and OEM style external coils).
- No external components allowed (coils, modules, ignition boxes, or crank triggers).
- Any module that will fit inside the distributor without any alteration is allowed.
- May use MSD pn 8728 rev-control with any rpm chip. Box must be mounted with rev limiter facing upward in an easy access area and out of reach of the driver.
- One OEM type alternator with internal regular is allowed and must me mounted to be belt driven off the front engine pulleys.
- Electronic traction control is not allowed.
- Must have one ignition kill switch mounted within easy reach of the driver and must be clearly marked “ON” and “OFF”
- ALL WIRING MUST BE EASILY ACCESSIBLE FOR INSPECTION.
- Must be steel OEM minimum at least 3 wheel brake system (disc/disc or disc/drum). Only right front may be omitted.
- No drilling, milling, or scalloped rotors allowed. No drums allowed with any holes other than OEM. Front rotors must be OEM or OEM replacement vented rotors. Rear rotors or drums must be minimum 0.810” width and 12” O.D.
- Single or dual aftermarket master cylinders and pedals allowed. Brake bias adjustment allowed within the reach of the driver. One proportioning valve may be installed on the right front and cannot be within the reach of the driver. Brake brackets must be welded to the housing.
- All components must be steel unaltered OEM in OEM location and match frame (steering shafts must have a joint every 5 ft., collapsible steering shafts highly recommended). Steel knuckles only. May be modified to suit the driver but must remain on the left side of the vehicle (no center steering)
- Steering wheel and quick release required may be aluminum.
- All components must be steel OEM, except for front upper control arms may be replaced with aftermarket, steel or aluminum cross shafts allowed. All components must mount in the OEM location except front upper control arm mounts may be modified and relocated. No aftermarket control arm mounts allowed.
- Adjustable spring buckets and spring spacers allowed. No jack bolts allowed on southern sportmod or hot mod chassis. Springs must mount in OEM location.
- No offset or bearing type bushings are allowed.
- Front ball joints may be replaced with OEM or OEM replacement only and may be tacked or welded in place.
- Sway bars are permitted, only OEM brackets may be used.
- OPTION 1 - (Southern sportmod or hot mod chassis)
- Control arms, upper and lower, must be made of steel OEM or fabricated. Fabricated arms must be made of square tubing and must be OEM mounting measurements. All control arms must be mounted in OEM mounts. Bolt holes may not be oversize or slotted.
- Jack bolts are not allowed, adjustable spring buckets are allowed. Spring buckets may be dropped but must be mounted in OEM location.
- Lower spring cups must be mounted in the center of the rear end housing.
- All suspension parts except for control arms must not be modified or altered. All suspension components must be steel (a magnet will be used to check components).
- No chains or cables allowed.
OPTION 2 - B-Mod chassis
- All components must be steel. No covers allowed
- All mounts and brackets must be welded or bolted solid.
- Coil springs must remain vertical and over center line of rear-end housing. No coil over eliminators allowed. No chains, cables or tethers.
- Rear shocks cannot be mounted on control arms. All rear control arms and panhard bars must be straight.
- Must utilized one of the follwing designs:
- Aftermarket three link design requrements: Must use 16" minimum 24" maximum lower control arms.
- 3rd link - Must use one upper control arm, solid tube only, located at top center of rear end housing and remain centered (one inch tolerance) on housing over drive shaft.
- Must use minimum 23" panhard bar located behind rear end housing.
- Lower spring perch must be welded to rear-end housing. BOTTOM OF REAR SPRING MUST REMAIN WITHIN 0.75 INCH OF THE AXLE TUBE.
- Must use steel upper weight jack. No floating or bearing rear spring perches/cups allowed, top or bottom.
- No suspension stops of any kind are allowed.
Shocks and Springs
- Only one steel shock allowed per each wheel. OEM mounted or heim joint shocks are allowed. Shocks on the rear must be mounted as close to OEM as possible. Rear shocks must mount on rear of the bottom control arm bracket and must mount in OEM location at the top.
- Front shocks must be in OEM location using factory mounts, except for Option 2 B Mods shocks must be mounted to lower control arm.
- No adjustable shock mounts allowed, mounts must be steel.
- Steel shock bolts or pins only, no aluminum or titanium.
- Coil over shocks are not allowed.
- Steel springs only. Springs must be at least 4.5” wide and one piece.
- No progressive springs allowed.
- OEM GM 7.5” rear ends, Ford 9” rear ends, and Ford 9”/Floater rear ends allowed.
- Housing must be mounted centered to the frame. No adjustable or floating mounts. All mounts must be securely welded and in factory OEM location. NO floating rear brakes.
- GM 7.5” rear end may be modified to accept Ford 9” axles. C-clip eliminators allowed.
- Rear axle must be locked. Gears may be welded, mini spools and full spools allowed. No lightweight spools allowed. Torque dividing differentials are not allowed.
- Housings must have a minimum 1” inspection hole in the back.
- Pinion angle may not be changed.
- No gun drilled axles.
- All rear end components must be steel, no aluminum or titanium.
Tires and Wheels
- Must use unaltered Hoosier 500 “IMCA” or Hoosier “H500” tires only. May use 27x8x15 or 26.5x8x15 tires only. No grooving allowed. Grinding and/or siping allowed only on tread contact area. Absolutely no chemical softening or and other alterations allowed.
- 15 x 8 steel racing wheels only. Beadlock allowed on the right rear only. Addition of the beadlock cannot add more than 0.750” to the overall width of the wheel. Homemade mud caps not allowed. Wheel covers or mudplugs allowed on the right side only. No bleeder valves. No wide 5 adapters.
- May use steel or aluminum wheel spacers with aftermarket racing studs but must keep overall width within 78”. Must use minimum 1” steel lugnuts. 0.625 studs recommended. Drilling rotors or hubs for lug pattern allowed.
- A 360 degree driveshaft loop (minimum 2” x 0.250”) is required and must be securely mounted no more than 6” rear of the front tube weld. Driveshaft must be painted white and labeled with your vehicle number.
- Engine must be mount a minimum 70” forward from center of the rear axle. Must be a minimum 11” from level ground to the crankshaft center.
- OEM or 45 degree solid engine mounts only. Must be made of steel.
- Steel or aluminum mid plate allowed.
- No vacuum/evac pumps allowed.
- Engine must be able to be used in a conventional car without modifications.
- Maximum of 368 cubic inches (370 C.I. for Mopar) is permitted. Note: Cubic inches will be checked. Maximum 3.484 stroke for GM.
- Maximum 175 lbs. compression ratio allowed.
- CRATE ENGINE: Must use unaltered sealed GM #88958602 or #19258602 crate engine. Upon inspection, any different, altered or missing GM seal bolts wil reslt in disqualification. GM seal bolt exception is IMCA approved and issued Cable-Lok rebuild system, and oil pan may be replaced by IMCA certified repair center with Kevko pan #1090NRHw/ISP and Kevko pick-up #1003-3/4. Must utilized required spacers, distributor, pushrods, valve springs or rocker arms.
- OEM steel passenger vehicle production block only. No GM Bowtie, Ford SVO or Chrysler W components allowed. GM approved block numbers are: 3892657, 3914660, 3914678, 3932388, 3932386, 3956618, 3970000, 3970006, 3970010, 3970014, 10066033, 10066036, 10243880, 14010207, 14010209, 14010287, 14016376, 14016379, 10054727, 14088528, 14088548, 14088552, 14093638, and 14101148. Stroke must match block. No 400 or larger cubic inch parts allowed. Steel only. Absolutely no machining allowed on the exterior of the block.
- Flat top or dish pistons only, no gas ported pistons. OEM or OEM appearing replacement steel crankshaft only – cannot be lightened no arrow wings, bull nose, knife edge or undercutting of 2nd or 3rd rod throws allowed. GM 5.7 or 6-inch stock appearing rod allowed only. All others must have stock rod configurations with stock appearing rods. Cap screws allowed. Aftermarket Rod bolts allowed.
- Must be unaltered approved OEM Head. Only GM OEM approved head numbers are: 14079267, 3986336, 3986339, 3986339X, 3986388, 3932441, 376445, 3928454, 3932454, 3876487, 3973487, 3973487X, 3973493, 3951598, 468642, 330862, 333882, 3998920, 3998991, 3998993, 3998997, 3970126. Maximum size valves on these heads are 2.02” intake and 1.60” exhaust. Valve springs must be stock diameter, no beehive springs allowed. Maximum 125 lb. seat spring pressure allowed. Screw-in studs, guide plates and poly-locks are permitted. Stud girdles are not allowed. May use Engine Quest (EQ) Stock Replacement (SR) cylinder head, part number CH350I, head must remain as produced, seat angles and valve sizes can not be changed: three angle valve job only (absolutely no casting removal in valve pocket of EQ head, for any reason); Ford – no aftermarket or SVO heads; Chrysler – no after market or W-2 heads, 360 cubic inch heads only 2.04” intake and 1.70” exhaust valves max for Ford and Chrysler. Bowl hog 80 degree maximum and may not be any deeper than 1.50” into pocket measured from chamber floor, not valve seat. Porting, polishing or alterations of any kind to heads block or intake is strictly forbidden.
- Full roller rocker arms allowed. No pedestal or shaft mount rockers allowed unless OEM for that engine.
- Conventional flat tappet cam/lifters only, cannot alter lifter bores. OEM firing order cannot be changed (GM: 1-8-4-3-6-5-7-2). NO VACUUM RULE.
- Cam must be chain driven, no belt/gear drives.
- Aftermarket performance harmonic balancers allowed.
- Intakes: Edelbrock (2701, 2176, 3721, or 2181), Weiand (7547-1, 7515, 7516, 7545, or 8323), any low rise stock cast iron 4 bbl intake (no marine, no porting or polishing, webbing on top may be removed up to 1” down)..
- A minimum (1) 1” plug above the oil level in the side of the oil pan is recommended. If not utilizing a plug, oil pan will have to be removed at time of inspection.
- Only 1 maximum 19” x 27” radiator allowed and must be mounted in front of the engine. Overflow tubes must be directed toward ground. Steel or aluminum V-belt pulleys only. Electric fans allowed. Aluminum water pumps allowed.
- Automatic transmission
a) Must be OE automatic with torque converter. All OE forward and reverse gears must be operational.
b) Torque converter must be a minimum 10” and must have a minimum one-eighth (1/8) inch plug, and contain three (3) quarts of transmission fluid. Must be able to hold brake while running and car will not die.
c) Must have approved scatter shield constructed of minimum 0.125 inch by three inch steel, 270 degrees around flexplate. Flexplate must be full, unaltered OEM, or OEM replacement. No manual bump starts allowed.
- Standard transmission
a) 3 or 4 speed transmissions. All OE forward and reverse gears must be operational.
b) Must have functioning 10.5" minimum diameter clutch and pressure plate bolted directly to steel flywheel. these components must rotate, consistent with engine rpm while car is in any gear.
c) Must have approved scatter shield constructed of minimum 0.125” by three inch steel, 270 degrees around flywheel. Flywheel must be full, unaltered OEM, or OEM replacement.
- Racing fuel cell required, maximum 32 gallons capacity. Must be mounted in a minimum 20 gage steel container. Must be mounted with two solid steel straps around the entire cell. Minimum 2” x 0.125”, behind the rear end and between the frame rails.
- Fuel cell must have a check valve in all vents including cap. Must have a aircraft style positive seal filler neck/cap system. A filler rollover check valve or flapper is required.
- Fuel cell must not be lower than the protective cage or tubing.
- NO regulators, bypass, pressurized, or return systems allowed.
- 1 fuel pump allowed. Must be pushrod/diaphragm style pump only and mounted in OEM location. No piston style, electric, or belt driven pumps allowed.
- One fuel filter allowed between the fuel cell and the carburetor. Must not be mounted in the driver compartment.
- Any air cleaner allowed. No ductwork, cool cans, or cold air boxes allowed.
- Carburetor: One 500cfm Holley carburetor allowed mounted with the fuel bowl facing forward only. May use Holley pn 4412 or Dorton 0-80583-1. Holley 4412 may be altered to meet the 0-80583-1 only. Aftermarket billet metering blocks without external jet adjustments and aftermarket billet baseplates may be used. Aftermarket baseplates must pass with go-no-go gage. Aftermarket floats allowed. No aerosol carburetors allowed. ABSOLUTELY NO GRINDING OR POLISHING ALLOWED ANYWHERE ON CARBURETOR. FACTORY CAST PART NUMBERS MUST NOT BE REMOVED. NO OTHER ALTERATIONS ALLOWED.
- May use one carburetor spacer no more than 1” thick. No adjustable throttle bore spacers. Carburetor gaskets and adapter cannot exceed 1.250”
- Gasoline only. Racing fuel allowed. No E85. No fuel additives or any other chemicals allowed in fuel at any time. Fuel may be subject to testing. Fuel will be tested with NO TOLERANCE!
- Zoomies, crossovers, tri-Y and 180 headers not allowed.
- Exhaust system must be mounted as to direct all fumes away from the driver/cockpit area.
- Aftermarket headers allowed (maximum 1.625 tubes, 3” collector). Maximum 9” collector allowed. Turn-downs allowed (maximum 10”). No alterations allowed to headers. Sensors, merge collectors, balance tubes, and extensions not allowed.
- Mufflers required. May be 3-ring, cone, perforated, or IMCA609 allowed.
- The overall weight of the racecar shall be measured at the conclusion of the event with the driver in the cockpit in full apparel. Minimum weight is 2,350 lbs. (B-Mod 2500 lbs)
- May use ballast. Must not be mounted in the driver compartment, outside the engine compartment or body, or on the rear bumper. Ballasts must be mounted with minimum (2) 0.500” steel fasteners only. No titanium, magnesium, stainless, or carbon fiber components allowed.
- All ballasts must be painted white and labeled with the car number.
- Any driver that finishes on lead lap and have competed in the prior two weeks competition may protest another driver that finishes in front of him or her. All protests must be submitted in writing within 15 minutes after completion of race. Once the protest has been initiated the protest cannot be recalled. All protests must be made in cash only and must be given to the appointed track official. All protesting drivers may be accompanied by one additional person. Protested drivers are allowed two additional people to aid with removing of protested parts. Teams are allowed 1 hour for removing any components except in the case a rod and piston need be removed in which 1 hour 30 minutes will be allowed. All teams are responsible for having tools necessary for disassembly. If components cannot be removed within allotted time the protested driver will be disqualified.
- Section protest – $250.00, $25.00 goes to track – Driver may protest suspension, engine, transmission, or fuel. If fuel is protested laboratory fees will be taken from protest fee. Protests may be anonymous, however, only protesting driver may be present.
- Complete protest - $425.00, $50.00 goes to track – Complete vehicle may be inspected, only one head may be removed, protesting driver chooses which side. If fuel is protested laboratory fees will be taken from protest fee. Protests may be anonymous, however, only protesting driver may be present.
- If protested driver is found legal, protest monies will be issued to protested driver less fees.
- If protested driver is found illegal, protest monies will be returned to protesting driver less fees and penalties will apply.
- Violations – First offense, Loss of points and winnings for current night. Second offense loss of points year to date and suspension up to four weeks in which decision will be made by track director.
- Any driver may protest a total of 2 times per season. A driver may only be protested by another driver a total of 2 times per season.
- SOS has the right to protest any driver at any time in which a $50.00 teardown fee will be given to protested driver if found legal.
- All decisions will be made by SOS officials and all decisions are FINAL.
- Any top four finishing driver may have their carburetor claimed by another driver finishing on the lead lap behind them for a fee of $500.00 or swap. Claimed driver has decision for cash or swap. Claiming driver must have competed for the prior two weeks of competition at SOS without disqualification. Claim must be submitted before leaving the race surface to an SOS official. Claimed driver is responsible for removing own components and must not leave the tech area until claim is complete. Drivers may be claimed a total of three times per season. If claim is denied penalty will be loss of points year to date and loss of current night winnings and will not be able to claim the remainder of the season. SOS has the right to claim after the third claim has been met.
- Claiming drivers will not be eligible to claim again for a minimum of two weeks and must compete a minimum of two consecutive events at SOS in class claiming, and achieving a top four finish in an “A” Feature main event.