PRO 4-Cylinder Rules
Dillon Motor Speedway PRO 4-Cylinder 2021 Rules
A. Minimum age for drivers is fourteen (12) years old.
2. COMPETING MODELS:
A. Any 1960 and later model with a maximum wheelbase length of 102 inches. FWD – TBD
B. Front or rear wheel drive car or truck. No all-wheel drive cars.
C. No two-seaters and convertibles.
3. CHASSIS AND ROLLCAGE:
A. The tech person will have the authority to disallow any car with compromised structural integrity or protruding parts that may be dangerous to a competitor.
B. Any chassis used must have come with a 4 cylinder engine option.
C. Complete 6 point center section and rear down bars must be 1 – 1 ½” minimum diameter and .090 wall thickness minimum. No exhaust tubing, or crimped exhaust pipe bends in main cage.
D. Main 4 points of roll cage must be welded to frame rail, or rocker panel. If welded to floor board, it must be welded onto a 6 x 6 metal patch and must be located no more than 6 inches from factory rocker panel.
E. No offset roll cages allowed. No small halos. Halo must extend to the RS to the middle of the passenger drivers seat would be mounted.
F. Minimum of 4 door bars on driver side, with rec 1/8 metal plate welded to outside of roll bars.
G. Minimum of 3 door bars on passenger side.
H. All perimeter bars and bumper bars must be shaped with safe and reasonably rounded ends to eliminate puncturing other drivers’ doors, tires, fuel cells, etc. No push bars outside of the front bumper cover.
I. All bars within driver’s reach must be padded.
J. All chassis suspension mounting points must be in stock OEM location. No exceptions. All left to right, height, and “x” measurements must be within ¼” of factory.
K. Rocker panels may be removed and replaced with tubing, provided the front and back of tubing are sealed.
L. All frames must be stock. Unibody frames may be tied together parallel end to end half way max on frame rails.
M. Front firewall, floorboard, and all suspension points must remain in factory location. No modifying for any reason. If floorboard has rusted or broke, you may patch weld, but do not remove and replace.
N. Must have full front and rear firewalls with no holes, completely sealed. 22 gauge steel minimum for patched sections, no combustible material allowed to fill holes.
O. Must have factory floor plan from front firewall ventricle section above transmission tunnel behind motor to front mount for back seat.
P. Inner structures of fenders, wheel wells, strut towers, and trunk floor may be removed.
Q. Frame may be notched for oil filter or fuel pump clearance.
If a OEM Chassis has been altered more than the rules above the car will have to run a 1″ restrictor plate! Tech Mans Decision!
A. Stock OEM style suspension that came on your car.
B. No aftermarket front control arms.
C. Front control arms may be interchanged within same make as long as both sides are the same length.
D. May not lengthen or shorten lower control arms on any make.
E. Stock style upper control arms may be lengthened or shortened for camber / caster adjustment.
F. No upper control arms added in place of stock strut designed car.
G. Any bushing allowed.
H. Max Tracking Width Rule 75in measured from outside edge of tire to outside edge of opposite tire.
I. May use any size, type, or arrangement of wheel spacers to make ride width maximum.
J. Wheelbase must be within +/- 1” of stock factory length for car model claimed. Left and right side of car must be within 1” of length of each other.
K. Strut rods on lower control arms such as Pinto and Toyota may be adjustable in length but retain stock mounting points.
L. OEM sway bars only. No splined type. 1 5/16” or 33 MM maximum diameter, mounting optional. End link design optional, may be adjustable on both ends.
M. Heim joints are allowed on sway bar and in place of tie rods for bump steer correction.
N. Any upper strut plate / connection may be used in place of strut tower.
O. Lemans bar between strut towers allowed.
P. Any caster / camber settings allowed.
Q. Adjustable rear shackles and slider blocks allowed on leaf spring cars.
R. Front eye of leaf spring must remain in stock location.
S. Rear pan-hard bars allowed only on cars which came stock with them. May be adjustable from under car only and with positive bolt pattern. (No screw jack)
T. Aftermarket upper and lower trailing arms for the rear is allowed.
U. Rear lower trailing arms cannot be adjustable and must be factory length. No heim joints on lower trailing arms.
V. Solid engine and transmission mounts allowed.
W. Spindles, rotors, and calipers must be OEM but may be interchanged within different year models or versions of your same chassis.
X. No aftermarket spindles. Spindles may be strengthened.
Y. Drum brakes may be interchanged with disc brakes within your same make.
Z. Brake adjusters, flow control, and metering valves allowed but MUST BE OUT OF REACH OF DRIVER and CANNOT BE USED DURING RACE.
AA. Single or double master cylinders allowed. Aftermarket pedals allowed and may be relocated.
BB. Steering box and rack may be interchanged among same make.
CC. Aftermarket power steering pump allowed.
DD. Brake air ducts allowed.
EE. Brake hats allowed.
FF. Drilling of rotor for cooling allowed.
GG. Steering quickner allowed.
HH. Quick release steering wheel highly recommended.
A. Any stock or aftermarket body, including straight sided dirt, fiberglass, aluminum, or steel aluminum. Open wheel type must submit photos for approval and will be allowed for one race maximum if approved.
B. Any car with an aftermarket roof made from fiberglass or aluminum will only be allowed with 54% left side weight.
C. Full windshield required. Rear side and rear optional. No door side glass allowed. Windshield must be lexan or safety glass laminated. NO PLEXIGLASS.
D. Two vertical braces at least 1” wide x 1/8” thick required on windshield.
E. Side view and rear view mirrors allowed.
F. Side vent for driver cooling allowed.
G. Roof escape flags as required by Bowman Gray are allowed.
H. All doors must be bolted, welded, or riveted shut.
I. No hood scoops, holes in hood, or anything else funneling air to the carburetor.
J. At least four (4) positive fasteners must be used to hold hood and trunk. OEM or fabricated hinges may account for two of these four total.
K. Rear spoilers will be a maximum of 5” tall and 54” wide. The highest point of rear spoiler must be at least 10” lower than the highest point on roof. Rear spoilers may have to be shortened or removed to meet the 10” minimum described.
L. Spoilers must be mounted at the back of the trunk area near the tail section.
6. SHOCK, SPRINGS, AND STRUTS:
A. One (1) steel bodied or strut per wheel. At least one end must be mounted in factory location.
B. Aftermarket racing shocks allowed. Heim join ends allowed.
C. No aluminum bodied shocks allowed.
D. No revalveable shocks or struts. No schrader valve type with external reservoir allowed.
E. Strut type can only be adjustable and not revalveable and/or replaceable cartridge in housing type.
F. Any aftermarket coil spring allowed. Rates optional. Spring dimensions are optional.
G. At least one end of spring must be in OEM location.
H. No bump stops.
7. ENGINE LOCATION AND TYPES:
A. Engine must be installed in stock location. There is to be no less than ½” between the back section of the cylinder head and the vertical plane of the stock firewall. No beating firewall back at this location.
B. All engines must use stock OEM parts with the only exceptions stated here. (see engine rules)
C. Four (4) cylinder piston engines only. No rotary engines. You may interchange engines and chassis within your manufacturer line but not across makes. Example: Any Ford in a Ford but no Toyota in a Ford.
D. No turbochargers or superchargers.
8. TRANSMISSION, FLYWHEELS, AND CLUTCHES:
A. Automatic or manual transmissions allowed. All gears must function from driver’s compartment.
B. Automatic (manual shift kits allowed. Reverse shift patterns allowed. Internal modifications for durability only. No trick or lightweight internal parts. OEM factory type only. Torque converter must be stock OEM size. Must be factory OEM stall speed. No stall or hollow converters. No aftermarket high performance converters. No valve or any mechanism to transfer transmission pressure allowed. Neutral safety switch must be functional at all times. Modified transmission pan allowed. Transmission cooler size and placement is optional. Cooling lines must have no more than 12” of high pressure rubber tubing. Aftermarket flex plate allowed.)
C. Manual (All gears must be functional from driver’s compartment. (3), (4), or (5) speed transmissions)
D. No aluminum flywheels permitted.
E. Any stock type flywheel and pressure plate combination with a minimum weight of 23 lbs. Weight will include flywheel, clutch disc, pressure plate, and bolts.
F. No aftermarket high performance clutch packs such as 10,000 RPM, ram, center force, etc. permitted.
G. Reinforcement in area of floorboard for safety is required.
H. No aftermarket transmission. Must be factory standard production only. No lightening of internal rotating components.
A. Standard one (1) piece, minimum diameter of 2 ½”. Steel only.
B. Must be painted white.
C. Driveshaft safety loops front and rear mandatory.
10. REAR ENDS:
A. Any car or truck rear end. Interchanging allowed within the same make.
B. Mounts on interchanged rear ends must match stock rear end to exact OEM measurements.
C. 9” Ford rear ends are allowed.
D. Any differential: open, welded, full spool, mini spool, locker, limited slip, or helical gear types allowed.
E. No quick change rear ends allowed.
F. Any gear ratio allowed.
G. No cambered rear ends. +/- 0.4 degrees maximum deviation.
H. Any aftermarket axle allowed.
A. Must be stock OEM production. No aftermarket blocks.
B. No block is to be coated, polished, or any machine work except what is listed here.
C. No machining to block for aftermarket rod clearance.
D. Blocks cannot be offset bored but may be sleeved with original bore centerline.
E. Stock OEM type rod, camshaft, and crankshaft bearings.
F. No maximum overbore.
G. Aftermarket pulleys and water pump allowed.
H. Crankcase evacuation system to header allowed.
I. Aftermarket oil pan allowed.
A. Must be stock OEM cast or steel, no aftermarket such as scat, lunati, etc. allowed.
B. Stock OEM stroke of crankshaft being used must be maintained within +/- .010”.
C. No lightening or knife edging of throws or counterweights.
D. May polish between #4 rod journal and #5 main journal surface areas for the purpose of identifying cracks more easily and eliminating surface stress risers, not to lighten.
E. Engine balancing allowed. Must be done in standard production manner.
F. Stud girdle kit allowed on main bearings.
G. Crankshafts may be interchanged among blocks within the same make with no machining needed. Direct fit applications only.
H. CC must be posted on hood and must be correct for your bore. Engines will be P&G tested regularly.
I. No 2.5 crankshafts allowed in Fords.
III. CONNECTING RODS:
A. Any steel aftermarket or factory rod allowed.
B. Maximum length for Ford is 5.7 inches.
C. Maximum length for Toyota is 5.2 inches.
D. All others; factory length rod.
E. May polish stock OEM rods.
F. No hollow aftermarket rods.
G. Toyotas may use H-beam rods if no block machining is needed.
H. Minimum 1.950” diameter rod journal for Fords.
I. Any rod bolt allowed.
IV. PISTONS AND RINGS:
A. Any flat top piston with any number of ring glands allowed.
B. Must have zero deck height.
C. No gas porting.
D. Any steel wristpin allowed. No titanium pins.
E. Any OEM dome piston engine may run any dome piston. The flat part of the dome piston may extend 0.010” above deck height.
F. Any style rings allowed. Minimum two (2) rings per piston.
V. BEARINGS, FASTENERS, AND GASKETS:
A. All engine bearings must be stock OEM type sleeve bearing. No roller bearings allowed.
B. No titanium fasteners allowed. Any other fastener allowed.
C. Head and main bearing studs allowed.
D. Any brand gaskets allowed. No O-ring style stealing allowed in place of head gasket.
VI. CYLINDER HEAD:
A. Must be stock OEM casting. No aftermarket heads allowed.
B. Heads may be interchanged on blocks within same make only in direct fit applications. Crossbreeding within same make is allowed. Example: 2300 head allowed on 2000 block
C. Angle milling allowed.
E. Stainless steel OEM configuration valves and swirl type allowed.
F. Valve stems may not be smaller diameter than stock for head being used without weight penalty. If valve stems are smaller than stock diameter, then competitor must drop their left side percentage from 55% to 53%.
G. No titanium valves.
H. Valves may be back cut 30 degrees maximum.
I. Valve stems may not be canted in head.
J. No interior de-burring, polishing, extrude honing, or acid porting allowed.
K. Ports must be stock as cast from OEM.
L. Lifter bore may be machined for solid adjusters.
M. Valves must retain stock diameter head.
N. Any steel or stainless steel retainer / keeper / shims allowed. Any type of valve job allowed. Valve job angles optional.
O. Any valve spring combination or design.
P. Reinforcement on cam boss allowed.
Q. Late Model Stock style bowl cut allowed. One (1) angle under the seat, 1” maximum depth of cut but do not touch the valve guide.
R. No blending of bowl cut to ports or rounding edges that bowl cut creates.
S. No roller cam followers allowed except on GM 151 engines.
T. Cam button allowed.
A. Any aftermarket hydraulic or solid cam allowed.
B. Adjustable cam gear allowed.
C. Stock OEM steel or double roller timing chain and gears with hex adjustment allowed.
D. Anti-pump up hydraulic lifters allowed.
E. No lightweight pushrods.
F. Only stock OEM rocker arms and lifters that came OEM in the head being used.
G. Oil return screens allowed.
H. Lifter valley baffles are allowed.
I. Lifters must be stock size for head being used.
J. Roller rocker arms allowed on GM engine only.
A. Stock OEM factory intakes with factory part number.
B. Fuel injection intake allowed.
C. No high performance or marine aftermarket intake manifolds.
D. No porting, polishing, coating, dipping, port matching, etc.
E. Intake may only be modified to accept carburetors. No other modifications allowed.
F. Carburetor adapter plate must not protrude down in plenum.
G. All parts must be mass produced items available as stock production over the counter parts. No special tests or marine type parts.
H. Only North American distributed intakes on domestic. Asian allowed on Japanese makes only.
12. CARBURETORS, SPACERS, AND ADAPTERS:
A. Holley 350 CFM # 0-7448, # 0-80787-1 OR Holley 500 CFM # 0-4412, # 0-80-583-1. No Holley Ultra XP500 allowed.
B. Choke hardware may be removed.
C. All vacuum ports must be plugged.
D. Two (2) gaskets @ .065 maximum allowed.
E. Any carburetor adapter or spacer, 1 ½” thick maximum.
F. Two (2) circular holes, one (1) oval hole, beveled and or tapered allowed.
G. No modification to carburetor for mounting.
H. 350 CFM or 500CFM must have choke horn.
I. Carburetors will be checked per NASCAR Late Model Stock guidelines.
J. No polishing, grinding, or machine work allowed.
K. No base plate modification.
L. Carb checked per the NASCAR rule book.
M. Boosters may be changed.
N. No booster modification to size or shape.
O. Height and location of the boosters must remain per factory specs only.
P. All boosters must remain OEM outside diameter only.
Q. Venturi area may not be altered or reshaped in any manner.
R. No altered gaskets, base plates, or drilling holes into the carburetor.
S. No butterflies to be thinned or tapered.
T. Idle holes may be drilled in butterflies.
U. Screw ends may be cut even with shaft, but screw heads must remain standard.
V. No shafts to be thinned or cut at all.
W. Accelerator pump discharge nozzle may be changed.
X. Power valves may be changed.
Y. Jets may be changed.
Z. No outside air to be pulled through the carburetor other than through the venturi.
AA. Anything not wrote in rules, will be teched per the NASCAR Late Model Stock carburetor rules.
13. AIR CLEANER:
A. All cars must have a metal air cleaner housing.
B. Aftermarket air cleaner up to 14 inches in diameter x 5 inches tall maximum allowed.
C. Paper element or K&N type allowed.
D. No funneling of any air to the air cleaner or carburetor.
E. Base of air cleaner must be below choke horn.
F. No carburetor hats, baffles, etc.
G. Top and bottom of air cleaner housing must be the same size.
14. FUEL & FUEL SYSTEM:
A. 100% Race Gas or 100% Non Ethanoil pump fuel gas. No mixtures
B. No additives.
C. No fuel cooling devices.
D. Twelve (12) gallon fuel cell maximum.
E. Fuel cell must be mounted in a can made of at least 22 gauge steel.
F. Fuel cell must be mounted in center of trunk area between the frame rails. No more than 2” deviation from center of rear treadwidth.
G. Fuel cell must be protected with a sufficient amount of structure, including a bar below and to the rear of the can.
H. Fuel cell venting high and to the driver’s side recommended.
I. May run high performance mechanical fuel pump or electric. If electric pump is used, you must have roll over valve and safety switch. This must be approved by tech person.
J. Fuel will be checked randomly.
15. ELECTRICAL SYSTEMS:
A. Battery must be securely mounted and enclosed to guard the driver from spills or explosions.
B. Batteries must be mounted in trunk or through floorboard but no lower than frame rails.
C. Only 12 volt electrical system allowed.
D. Standard or electronic distributor may be modified for reliability only.
E. Stock type coils only.
F. MSD, Accell, Mallory, etc. Internal parts, coils, or modules are allowed, stock type only.
G. No magnetos.
H. No multi spark discharge boxes (MSD) allowed.
I. Points type allowed.
J. No full aftermarket distributor allowed.
K. No adjustable timing controls.
L. No traction control devices.
M. All wiring in car must be securely insulated and fastened.
N. Any spark plug wires allowed.
O. Any spark plugs allowed.
P. No dual point distributors allowed.
Q. Mel’s distributors allowed.
16. COOLING SYSTEM:
A. No Antifreeze. See track fine in general rules.
B. Stock cooling system only in stock location.
C. Any radiator allowed.
D. May use water wetter type products.
E. Electric fan allowed.
F. Overflow hose must be mounted to base of windshield passenger side to alert driver in case of overflow or to a sealed catch container in the trunk area.
G. Fabricated mounting for the radiator allowed. Must be mounted between frame rails.
17. EXHAUST SYSTEM:
A. Any stock or aftermarket exhaust manifold or header allowed.
B. 4 into 1 and tri-Y style allowed.
C. Exhaust pipes must route to behind the driver’s seat, and must extend to the outer edge of the car.
D. No exposed pipes in driver’s area.
E. Exhaust may run through the inside of car if totally boxed, sealed, and approved by tech person.
F. No pipes turned down.
G. Mufflers allowed.
H. Crankcase to exhaust evacuation systems is allowed. Only quality check valves will be permitted.
18. OILING SYSTEM:
A. Stock type wet sump only.
B. External oil filter and coolers allowed. Must remain under the hood with steel braided hose and any type fittings. No rubber hose or hose clamps allowed.
C. No dry sump or accu-sump systems allowed.
D. Any aftermarket racing oil pan allowed.
E. Screen kits in oil return system allowed.
F. Oil pan baffles preventing oil from flowing away from the oil pump pickup allowed.
G. Windage trays allowed.
19. GROUND CLEARANCE:
A. All heights are measured with the driver in race trim.
B. Front spoiler minimum of 4 inches.
C. Center of crankshaft bolt to the ground, minimum of ten (10) inches.
D. Frame height minimum of 4 inches, measured at the frame rail or rocker panel.
E. Fuel cell and / or fuel cell frame minimum 8 inches from lowest point to the ground.
F. Oil pan minimum to the ground is 4 inches.
20. WHEEL AND WHEEL SPACERS
A. 8” maximum width
B. 13-14” diameter only.
C. Steel wheel only.
D. Any wheel stud diameter and length allowed.
E. Offsets on all 4 wheels do not have to match.
F. No pressure relief valves allowed.
G. No wheel weights allowed.
H. May use any size, type, or arrangement of wheels spacers to make ride width maximum.
A. All weight and weight percentages are measured with driver in car in race trim.
B. Advertised engine size in CC and left side weight percentage to be located on the hood, so tech person can read it when you roll onto the scales.
C. 5 gallons of fuel can be added for post-race weigh in.
D. 5 gallons regardless of fuel cell size or number of laps run.
E. All cars will weight one pound per CC after race with a minimum of 2050 lbs for Toyota 3TC Car.
F. All Ford engines, minimum weight of 2300 lbs. 1 lb per CC above 2300 CC.
G. Toyota 20R block with 22R head must weigh 1 pound per CC.
H. Ford 2300 head on 2000 block must weigh 2300 lbs.
I. Ford Pinto / Lima style engine with 1.50” intake and 1.75” exhaust valves may compete at 2300 lbs.
J. Maximum left side weight is 55% of the total weight unless told to be less by tech person.
K. No dislodged parts can be added back to the car after race to make weight.
L. All lead must be in blocks and painted white with car number on it. All weight must be securely bolted.
M. Any chassis design or car make that has an obvious advantage over any other may be subject to weight percentage and weight additions for the sake of close competition. This will be determined by tech person.
A. Must have good seat belts. 5 point harness minimum. If no date, then replace.
B. Helmet (Snell SA95 or better required)
C. Flame retardant driving suit with minimum SFI-1 rating required. SFI-5 highly recommended.
D. Flame retardant gloves and shoes highly recommended.
E. Neck collar, or head & neck device highly recommended. Example: R3, Hans, Hutchens, etc.
F. Aluminum racing seats only.
G. Approved window net required.
H. 2 ½ lb fire extinguisher with a dial, must be located within reach of driver or a switch to activate a fire suppression system.
I. Master kill switch must be mounted within easy access of driver and also safety crew members from outside of car.
A. The track approved tire will be the Hoosier 800, Hoosier 790, DOT (300+ TW), or Scuff Goodyear 2714.
B. Tires must be inspected, approved, and recorded prior to race to be eligible for competition.
C. No soaking, grooving, siping, camber cutting, or treating tires in any way. Sniffer, durometer, and black light will be used in pre and post-race inspection.
D. If you are caught soaking or treating your tires in any way, all four of your tires and rims will be confiscated and not returned.
E. Tires are subject to be checked at any time by a track official.
Any Car May Be Allowed To Compete With A Weight And/Or Restrictor Plate At Tech Director Determination. Tech Director Decision Is Final.*** ALL RULES SUBJECT TO CHANGE TO KEEP COMPETITION FAIR FOR EVERYONE *** Front Wheel Driver Cars Please Contact Speedway Before Competition.
A Race Car That Is Legal For The Pure Stock Rules At DMS Is Allowed to Compete In This Class