2021 SK Modified® Rulebook

2021 SK Modified® Rules

For any technical questions, please thoroughly read these rules and any applicable NWMT rules, then email tech@staffordspeedway.com.

2021 SK Modified® Rules Available in PDF format

2021 SK Modified® Rule Changes



The rules herein shall refer to Stafford Motor Speedway as “SMS”. These rules are intended to create safe, affordable and fair competition. While they offer a good outline, every item cannot be covered by a written rule. If you have questions regarding something not detailed in these rules, please consult an SMS Official for clarification before proceeding. These rules are for SMS only with no expressed or implied agreement with any other speedway or series as to their interpretation, implementation and method of inspection by their technical inspectors and officials. No car, component or equipment will be considered as having been approved by reason of having previously passed through inspection unobserved. No car, component or equipment will be considered as having passed inspection for the event until the finish is made official. The request for new or modified parts or components not specifically addressed in the current version of this rule book must be submitted in writing, via email, to tech@staffordspeedway.com for consideration of approval on or prior to August 1, 2020 unless otherwise authorized by SMS to be considered for competition for the 2021 season. 

All equipment is subject to the approval of SMS Officials. You may be assessed penalties including but not limited to: added weight, fines, loss of points, loss of handicapping, or suspension for car parts, components, and/or equipment deemed as not in compliance with these rules. Any car part, component, and/or equipment which does not conform to specifications or tolerances contained in the 2021 rule book or is not otherwise approved by SMS may not be used in competition in 2021.

By engaging in competition at SMS, you hereby agree to have read the 2021 NASCAR Whelen Modified Tour (NWMT) Rulebook, the NASCAR Weekly Racing Series (NWRS) Rulebook, the SMS General Rulebook and the SMS SK Modified® Rulebook.

All 2021 NASCAR Whelen Modified Tour (NWMT) rules and the 2021 NASCAR Weekly Racing Series (NWRS) rules, where applicable, will be enforced for the SMS SK Modifieds®, with the following changes and/or additions (EIRI).

SMS Officials decisions regarding rules are final and non-appealable.

DRIVER ELIGIBILITY – All drivers must have a Stafford Speedway SK Modified® driver’s license. Drivers competing in the SK Modified® division at SMS will not be permitted in the Street Stock, Limited Late Model, or SK Light Modified divisions on the same event date. Drivers must be minimum 16 years of age.

20E- 1.3 APPROVED COMPETITION MODELS– Approved model bodies are listed in the NASCAR Rulebook. Other models both domestic and foreign steel passenger cars may be approved for the SK Modified® division providing they are the same in body configuration and meet the spirit and intent of competitive racing in the SK Modified® division. Detailed chassis, body and interior tin rules can be found in the NWMT rule book. You may not compete without the roof, windshield, hood, and air filter assembly in place. Additionally, the bumpers and all nerf bars must be adequately secured to the chassis at all times. SMS Officials will pass judgment on any body / bumper / nerf bar damage prior to continuing an event. Their decisions are final and non-appealable.

20E- 2.2 OVERALL CAR WEIGHT – All specified weight requirements will be with the driver. The minimum weight at all times will be 2,645 pounds. MOPAR engines over 359 cubic inch displacement must add 6.8 pounds per cubic inch over 359. No car will be allowed to have more than 56% of the total weight as the left side weight. Proper bore & stroke for engine type must be maintained. Any car found to be under the minimum overall car weight allowance will be penalized one position for every pound under the minimum total weight.

20E- 2.3 ADDED CAR WEIGHT – Added weight must be in block form magnetic steel or lead only of no less than five (5) pound blocks (no pellets). Added weight must be securely bolted to the frame rail and painted white with the car number stenciled in black. No added weight will be permitted inside the driver’s compartment. Weight must be welded in a box or attached with two or more “grade 8’ bolts minimum 7/16” diameter.

20E- 2.4 CAR WEIGHTS AFTER RACE – Nothing may be added to or taken from the car to make total or left-side weight. Gas, oil or water may not be added. Wheels and tires cannot be changed, but an amount equal to one half of one percent (.5%) of the gross weight will be added for loss in weight due to race wear (minimum post-race weight of 2632 lbs.). Any car found to be under the minimum overall car weight allowance will be penalized one position for every pound under the minimum total weight.

20E- 3.2.3 SIDE WINDOW GLASS/WINDOW NET – A nylon window net must be installed in the left side door window opening, and it must be positioned to cover the entire window opening. Window net should not be used beyond three (3) years from the date of manufacture. The window net must be rib type, made from minimum ¾ inch, maximum one (1) inch wide nylon material with a minimum one (1) inch and a maximum 2-1/4 inches square opening between the ribs. The minimum window net size must be must be 22 inches wide by 16 inches high. All window net mounts must be a minimum ½ inch diameter solid steel rod on the bottom and a minimum one (1) inch wide by 3/16 inch thick flat steel or a minimum ½ inch diameter solid steel rod on the top, with mounts welded to the roll cage. The window net, when in the closed position, must fit tight and be secured with a lever-type quick release latch acceptable to SMS Officials. The lever must be secured by a detent ball in the lever and may be supplemented by Velcro® fastener only – pins or clips will not be permitted. The latch must be mounted at the top in the front to roof bar (#3) release from the inside.

WINDSHIELD – A flat windshield is mandatory, per the NWMT rulebook, made of a minimum of 1/8” polycarbonate that extends from the left A-pillar to the #4A center windshield bar and from the roof to the cowl. A minimum of three Dzus type fasteners must be used on each of the four sides.

20E- 3.2.5 REAR VIEW MIRROR – One (1) rear view mirror must be mounted at the top of the windshield. If running a head and neck restraint system, you may run a 14″ X 2″ mirror. If not, the mirror must be no larger than 8” X 2”. No multi-image or side mirrors. Oversized mirrors maybe blacked out by the use of paint only, to obtain the 8” X 2” maximum reflective area. Spot mirrors of any size/type are not permitted.

20E- 3.5 DOORS – Door panels may be made of magnetic steel or aluminum. Aluminum crush panels must be installed per the NWMT rulebook.

20E- 3.6 QUARTER PANELS – All quarter panels may be made of aluminum or magnetic steel.

INTERIOR SHEET METAL – The rear center panel (over the fuel cell) must be made of magnetic sheet steel, 22 gauge, .031” thick, with a minimum width of 28”, and must extend from the rear vertical panel forward to the #7 roll bar, per the NWMT rulebook.

20E- 3.8 HOODS / ROOF-
C. All roof panels must be made of magnetic sheet steel, or be an SMS approved manufactured fiberglass roof panel. All cars utilizing an approved fiberglass roof must install the (minimum) 1/8” thick aluminum anti-intrusion plate in the roll cage halo as described in the following diagram. For additional specifications on letters A. B. D. E. and F. see the NWMT rulebook. Cars may not compete without a roof or a hood.

20E- 3.11 IDENTIFICATION – All car number configuration and design is subject to approval by SMS Officials. Only single or double-digit numbers will be permitted. The size, color, and style of numbers must be adequate to permit prompt identification by SMS Officials at all times. Numbers must be solid color, at least 18 inches high, measured vertically, excluding borders and silhouettes, must be neatly attached to or painted on both sides of the car on the center of the door. Door numbers must be a minimum of four (4) inches in width, and slant no more than 30 degrees from vertical. The tops and bottoms of all numbers must be even (not staggered). Two (2) digit numbers must not overlap and must have a minimum of ¾ inch separation. A solid number 18 inches high, excluding borders and silhouettes, must be neatly attached to or painted on the roof, reading from the passenger side. A solid number a minimum of 12 inches high, excluding borders and silhouettes reading from the passenger side neatly attached to or painted at a 45 degree angle on the right front corner of the roof is also acceptable. Solid numbers, as large as possible, must be attached to or painted on the right outer nose and taillight covers. The use of number decals is acceptable if SMS Officials determine that the number is legible. Numbers, lettering, and paint schemes that utilize mirror or foil must be pre-approved. All schemes and colors are subject to SMS approval.


These SMS Spec Engine rules are intended and designed to create a standardized rule package to reduce cost, increase the level of competition, and to promote a better technical atmosphere by involving the engine builders in the process of technical inspection. To help keep the full integrity of the Spec Engine program intact, any published engine builder whose engine finishes in the top three may be involved in the tech process.

20E- 5 GENERAL SPEC ENGINE REQUIREMENTS- The only approved engine for Spec use is the Chevrolet 350. All parts for the Spec Engine must maintain manufacturers overall dimensions and weight. All Spec Engine parts must be installed as supplied, with no machining or modification except where noted. These SMS Spec Engine rules are intended to create a standardized rule package to reduce cost and increase the level of competition. With the exception of engine machined components, all Spec Engine listed parts and components must be used as purchased, with no modifications permitted, unless otherwise noted. We will add a list of Spec Engine component part numbers.


All Spec Engines must use the following parts, approved part numbers are as follows:
GM BLOCK – 10066034, 3970010, 3970014, 14010207, 14010209, 14011064, 14016379 , the DART SHP, or any pre-existing GM Bow-Tie block. PISTONS- Wiseco Pro Tru-PT003H, JE SPR-157076, or Manley 5915 must be used. The ring package used (type and thickness) must be the one designed for the piston used.
RODS- Manley-14101-8, 14050R-8, or Crower Sports Rods- SP3205
OIL PAN – Any pre-approved aluminum pan or Canton 11-196.
VALVES- Manley Intake 11596 or 11864, Manley Exhaust 11543 or 11863
CRANK- Scat Cast or Steel – 9-350-3480-5700, Callies Comp Star Series, or Manley 190190.
INTAKE- Edelbrock 7101
Carb Spacer- Big Haus USA part 002
HARMONIC BALANCER- ATI 917260 or 917320 or BHJ CH-IBS-6-C or Power Bond PB1012-SS.
The maximum decking of the block is 9.00”. Angle milling of block deck is not permitted. Offset dowel pins are not permitted. De-flashing, grinding, welding or painting of any internal area is not permitted. Maximum overbore is .060″. A maximum static compression ratio of 11.0 to 1 is permitted.

20E- 5.5 PISTONS/RODS Wiseco Pro Tru-PT003H, JE SPR- 157076, or Manley-5915 piston must be used. Manley-14104-8 or 14050R-8, or the Crower Sport Rod- SP3205 must be used.
A. The approved piston must retain all its manufactured dimensions and weight. The JE and Manley pistons must maintain a 2.50” pin length. Wiseco pistons must maintain a 3.00” pin length. Additional gas porting of any type is not permitted. All rings must be installed, working and of magnetic steel. Stainless, z-gap, gapless, or Dykes type rings are not permitted. No portion of piston may protrude above the top of the block. The minimum ring thickness permitted is as follows: Compression rings .043″ Oil ring assembly 3mm.
B. Only magnetic steel non-coated piston pins maintaining a minimum diameter of .927” inch are permitted. They must be contained by bushings only (no bearings of any type). Full floating pins are permitted. Wrist pins may not be coated.
C. Piston pin holes must be in a fixed location in the piston and connecting rods.
D. Only two-piece insert style connecting rod bearings are permitted.
E. The approved rod must retain all of its manufactured dimensions and weight. Only normal engine balancing and the use of after-market bolts and nuts are permitted. No de-burring, de-flashing, polishing, grinding or lightening is permitted. Rod length must be 5.700”.
G. Minimum weight for piston, pin, ring, bearing and rod assembly is 1168 grams.

20E- 5.5.4 OIL PAN – Dry sumps, external oil pumps or tanks or accu-sump systems are not permitted. The Canton 11-196 steel pan or any pre-approved existing aluminum oil pan may be used. Oil coolers are permitted. Only OEM in the pan magnetic steel type oil pumps are permitted. No pumps of any type may be used in the evacuation systems.

20E-5.6 HEADS – The Dart 10024266 cylinder head casting must be used. The casting part number must be purchased as completely produced by Dart, custom ordering of partial production/finishing is not permitted. The Dart casting is produced with, and must maintain a 60cc combustion chamber, a 2.02” intake valve and a 1.60” exhaust valve. Machining the valve guide bosses for seals and machining the gasket surfaces is permitted. The addition of screw-in studs, guide plates, valve spring seats, valve seals, poly-locks or jam-nuts is permitted. Coolant lines are permitted on the front/rear ends of the heads. Coolant lines are not permitted on the side of the head. Max Intake port volume is 177cc. Max Exhaust port volume is 71cc. Head gasket surface milling tolerance for SK Modified® is 0.00″ to 0.050″ from true 23.00 degrees of stock valve position. The Intake to pin measurement must be no less than 6.050”. No other machining or modifications of any kind are permitted. The ports/runners, combustion chamber, the valve angle and location must remain as produced by Dart. The EGR port may be blocked off at the intake gasket area only, by use of a metal shim on one surface of the gasket. The exterior of the casting may be painted. A maximum of 2 intake mounting holes may have HeliCoils. Intake and exhaust mounting holes may not be added or relocated. Holes must take standard dimension bolts.

VALVES- The Manley intake valve 11596 (111 grams), Manley intake valve 11864 (114 grams), Manley exhaust valve 11543 (95 grams) or Manley exhaust valve 11863 (102 grams) must be used. Valve stems must have a minimum diameter of 11/32 inch. Valve lifter weight is 85 grams minimum. All parts must maintain production dimension and weight.

VALVE JOB- When cutting the valve seat angles, no stone or grinding marks are permitted above the bottom of the valve guide. All cutting in reference to the valve job must be centered off the centerline of the valve guide. Competition style multi-angle valve job is permitted. The bowl area must pass the 360 degree “ball” check (the appropriate sized ball must not fall into the guide area when rolling around on the valve stem). Intake is a .787” ball. Exhaust is a .531” ball. Surfaces and/or edges where the cutter or stone has touched must not be polished. No hand grinding or polishing is permitted on any part of the head.

VALVE SPRINGS & RETAINERS- OEM Stock type magnetic steel retainers that weigh a minimum of 30 grams (retainer only) must be used. Valve springs may be single or double springs, but must be parallel wound. Barrel wound, conical wound springs, or beehive type springs are not permitted. Double springs must have a diameter between 1.450” and 1.437”. Valve springs must have a height of 1.700” to 1.800”. Retainer locks must be magnetic steel, and must be Machine 7 degree, Super 7 degree, or 10-degree types only.

The Scat Cast or Steel Crank 9-350-3480-5700, Callies Comp Star series crankshaft, or the Manley 190190 may be used. The main and rod journal sizes are .020” under for the main and .030” under for the rod journals. Stroke must be 3.480”. If you are currently converting an existing SK Engine over to the SK Spec Engine, you may use your existing GM cast or forged steel crankshaft, and it must weigh a minimum of 50 pounds and must be 3.480” to 3.495” in stroke. You must contact the SMS Tech Staff to notify them of your intent to run this pre-existing crankshaft.
B. Small journal or Honda pin crankshafts are not permitted.
C. Machining or polishing of the crankshaft counterweights is not permitted. Normal standard engine balancing is the only acceptable modification that can be performed on this component. No painting or Teflon coating. No capping of the counterweight holes. Crankshafts must maintain the manufacturer’s dimensions.
D. Minimum crankshaft weight is 45 lbs for the SCAT, Callies, or Manley crankshaft, and 50 lbs for the old style SK pre-existing crankshaft.
E. The Power Bond PB1012-ss, ATI 917260 , 917320,or the BHJ CH-IBS-6-C harmonic balancer must be used.

20E-5.8.1 CAMSHAFT- K15 or P55 cast core camshafts must be used (Billet steel cores are not permitted). The maximum camshaft bearing journal size is 1.875″ (475mm). Camshaft may not exceed .550” +/- .005” lift at the valve with zero lash.

20E – 5.8.2 VALVE LIFTERS-
An 842” diameter magnetic solid steel valve lifter must be used. Roller tappets, ceramic valve lifters, tool steel solid lifters, mushroom valve lifters, and any type of mechanical assistance exerting a force to assist in closing the valve and/or push rod commonly known as rev-kits are not permitted.

B. Valve lifters can weigh no less than 85 grams.

20E- 5.8.3 ROCKER ARMS- Aluminum or stainless stud mounted roller rocker arms are permitted. 7/16” studs may be used. Steel 5/16” x .080” minimum wall push rods must be used. Chevrolet must run 1.5 ratio rockers. Stud-girdles are permitted, aftermarket shaft rocker systems are not permitted. Competition Cams rocker part number 1604 will be permitted.

20E- 5.9 INTAKE MANIFOLD– A second generation Edelbrock 7101 intake manifold must be used. There are no modifications or alterations permitted to the intake manifold. No porting, polishing, acid dipping, deburring, de-flashing, abrasive cleaning, internal painting, milling, cutting, drilling holes, enlarging bolt holes, matching of ports or welding. An SMS supplied intake manifold must fit your engine complete with stock gaskets. All bolt holes must be in alignment and same size as stock. Coolant lines are only approved from the water neck to the back side of heads. The maximum thickness allowed for the Intake gasket is .064”. Note: SMS Officials reserve the right to swap competitors intake manifolds as part of their routine post-race tech process.

The Big Haus USA 002 spacer must be used. One gasket per side, maximum gasket thickness of .075” permitted. The spacer may not be modified in any way. Additional openings for the induction of air is not permitted. Carb and spacer mounting hardware must be solid and must not permit air to pass through or by.

20E- 15 FUEL SPECIFICATIONS – The only approved fuel is Sunoco Supreme. Sunoco Supreme is available at Stafford Motor Speedway.
A. Icing or cooling of the fuel system is not permitted in the paddock, pit or racing area.
B. Gasoline may be tested and certified at any event through the application of various chemical analyses as considered appropriate by SMS Officials. Gasoline may be checked before, during and after the racing events.
C. Nothing may be placed in the fuel line other than a standard fuel filter. The use of any type of fuel catalyst or other fuel-altering devices is prohibited.

SK Spec Engine must use the following headers:

Flowrite: Troyer 3025, CD 3035, Spafco 3055, Raceworks 3045
Kooks: Troyer SMS1048, CD SMS1438, Spafco SMS1348, Raceworks SMS1253
Beyea Performance: AMSST-23S1-SK
B. Headers must remain as manufactured, no modifications may be made to the headers.
C. The exhaust header flange must mount directly to the cylinder head with no spacers between the flange and the cylinder head. Header flange thickness may not be altered.
D. Inserts are not permitted in any part of the header or collector. Only one (1) collector allowed per side.
E. Turn-downs must be used after the mufflers, on each side. The turn-downs must be installed so that hot exhaust, engine debris, or engine flames are aimed at the ground (from pointing straight down to less than 90 degrees to horizon).
Kooks R35-30-10 or R35-35-10, the Flowrite FR-300 or FR-3500, or the Beyea Performance MUF3.5-SK mufflers must be used. The Muffler must be 3.5” on the inlet and outlet. Mufflers must be removable for inspection.

G. Thermal wrap is not permitted anywhere on exhaust system.
H. Only one muffler and exhaust pipe allowed per side.
Exhaust system subject to approval by SMS Officials.
J. Interior coatings are permitted.

NOTE: The life expectancy for all mufflers are two years. All owners are responsible to make sure their mufflers are in proper working order. If found not to be, the muffler will be deemed illegal (i.e. missing one or more of the internal baffles).

The Quarter Master 298108 or 298158, 7-1/4” two disc V-Drive, with an SFI rated 153 tooth steel OEM type ring gear/flexplate that weighs a minimum of 4.1 pounds may be used with the SK Spec Engine. Optional stock type clutch rule: A Stock OEM dimension 153 tooth steel flywheel and 10” steel clutch and pressure plate may be used. OEM type steel pressure plate and steel disc only. Solid type disc only, no paddle or button type discs. Minimum diameter 10″ clutch and pressure plate. Drilling or lightening of any part is not permitted. Steel bolts only. Flat surface machining allowed only on the face of the flywheel, any cutting on the back side of the flywheel will deem the part illegal. Spec Engine flywheels must weigh a minimum of 9 lbs (without bolts) and be one of the following part numbers:

10,000 RPM 1019-9.5
Magnus MRPBF-95
Ram 851

20E- 5.10 CARBURETOR – A Holley two-barrel model 4412 carburetor must be used.  Only Holley replacement or service parts can be used in any carburetor rework. Carburetors and/or carburetor components machined from billet materials are not permitted. All parts must be a Holley manufactured part for the 4412 model. Polishing, grinding, resizing or reshaping of any part or orifice is not permitted. The body, base plate, metering block, and bowl must be a standard Holley 4412 part, HP parts are not permitted. OEM type gaskets, jets and power valve must be used. The diameter of every hole in carburetor must pass the standard NASCAR /SMS pin and tooling gauges as part of our routine tech process.
(1) Body of carburetor and metering block: No polishing, grinding or reshaping of any part. Drilling of additional holes or plugging holes is not permitted.
(2) The choke may be removed, but all screw holes must be permanently sealed.
(3) Choke Horn: Choke horn may not be removed.
(4) Boosters: Boosters may not be changed. Size or shape must not be altered. Height must remain standard.
(5) Venturi: Venturi area must not be altered in any manner. Casting ring must not be removed.
(6) Alterations to allow additional air to be picked up below the opening of the venturi such as altered gaskets, base plates and drilling holes into the carburetor will not be permitted.
(7) Base Plate: Base plate must not be altered in shape or size.
(8) Butterflies: The stock Holley 4412 or Stainless Steel Holly part #346 butterflies must be used. They may not be thinned or tapered. The Butterflies must remain as manufactured, and must maintain the Holley production tolerance thickness of .0438” to .0398”.  Idle holes may be drilled in butterflies. Screw ends may be cut even with shaft but screw heads must remain standard.
(9) Throttle Shaft: Shaft must remain standard and must not be thinned or cut in any manner.

Only a round dry type paper air filter element maintaining a minimum 12 inches and maximum 14 inches diameter will be permitted. The air filter element must maintain a minimum of 1½” inches, maximum five (5) inches in height. All air must be filtered through the element.

B. Only a round metal filter housing will be permitted. The top and bottom of the air filter housing must be solid with no holes. A maximum of one (1) inch lip will be permitted from the air filter element to the outer edge of the air filter housing top and bottom. The air filter housing carburetor mounting ring must have only one (1) round hole a minimum of five (5) inches in diameter. It is permissible to attach a shield to the front area of the air filter housing up to a maximum of one half of the air filter circumference. The shield must not be higher than the height of the air filter element. The air filter housing metal top and bottom must be of the same diameter. The air filter housing must be centered side to side and set level on the carburetor. No air induction, ducts, baffles, tubes, funnels or anything else which may control the air entering inside of, or between the air filter and carburetor. No plastic air filter housings or parts.
C. The bottom of the air filter element must measure within one (1) inch of the carburetor’s top flange. A spacer may be used between the carburetor and the air cleaner so long as the one (1) inch specification is not exceeded.
D. No portion of the hood may be higher than the bottom of the air cleaner.
You may not compete without the air filter and air filter housing in place.

20E- 6.1 IGNITION SYSTEM – NASCAR approved ignition system must be used. Electronic distributors are permitted. All electronic distributors must be in stock type housings, have stock type controls and modules, be equipped with a magnetic pickup, be gear driven, and be mounted in the stock location. Billet distributor housings are permitted.
B. Single or dual point camshaft driven distributors are permitted.
C. Only one (1) ignition coil is permitted and must be mounted on engine side of the firewall.
D. Electronic firing module amplifier box is not permitted.
E. Computerized, multi-coil, dual electronic firing module box or crank trigger systems are not permitted. Magnetos are not permitted. All ignition systems are subject to approval by SMS Officials.
F. Adjustable timing controls are not permitted.
G. Retard or ignition delay devices will not be permitted.
H. Only MSD 8727CT or 8728 External RPM limiters may be used. The violet wire must be cut back flush to the unit’s housing, with the green and the white wires run directly to the coil negative, mounted on the engine side of the firewall in plain view.
I. Accessories to regulate the power supply are not permitted.
J. The tachometer wire must run from the distributor to the tachometer along the #8 dash bar separate from any other wires and in unobstructed view for inspection. The tachometer wire must be isolated from any other wires, connections or devices. The entire length of the tachometer wire must be visible from distributor to the gauge.
K. The Vacuum advance unit may be replaced with a manual non-electronic timing adjuster that does not extend more than two inches beyond the distributor housing.

20E- 6.3 ALTERNATOR – A functioning 12-volt single alternator system is optional.

20E- 6.4 STARTER – A stock type starter must be used. The starter must be in stock position and operative at all times.

20E- 6.5 BATTERY  One (1) 12-volt Gel or Glass Mat type battery with a minimum weight of 17 lbs is mandatory. The battery must be located between the frame rails under the hood or the floor of the car. If located under the floor, the battery must be completely encased, if located under the hood the battery must have a suitable cover. The battery must not be forward of the radiator or rear of the rear end housing of the car. The battery location must be acceptable to SMS Officials.

20E- 6.7.1 RADIOS
The in-vehicle radio must be analog only and must not be capable of transmitting or receiving in a digitized, encrypted or scrambled format as determined by SMS /NASCAR. Keypad style and/or password protected radios will not be permitted. Scanning and/or channel hopping transmissions to or from the in-vehicle radio will not be permitted. All transmissions to and from the in-vehicle radio must be in the 450.000MHz-470.000MHz UHF range. The in-vehicle radio is not permitted to transmit or receive any type of telemetry (data) signal or information other than audio communications and must remain independent from any electronic system in the vehicle. Teams will not be permitted to rebroadcast transmissions to or from the in-vehicle radio at any time during an Event. It is strongly recommended that all in-vehicle radio frequencies be licensed for use by the Federal Communications Commission (FCC) and meet all applicable regulations and guidelines.
B. Only one (1) SMS / NASCAR-approved, two-way radio and one (1) radio push to talk button will be permitted. It is not permitted to have any frequency of any Competitor installed in the radio at any time. The vehicle is permitted only one (1), approved radio wiring harness.
D. At all times during practice(s), qualifying and the Race the spotter must have radio communications with the driver and must monitor the SMS Race Control frequency. Spotters must be in the designated spotter location at all times during competition. The radio frequency being used will be made available to SMS Officials.
E. Driver to driver radio communications will not be permitted.

20E- 6.7.2 SPOTTERS – Spotters are mandatory. Every car must have a spotter monitoring SMS race control by way of scanner or radio, located in front of SMS Race Control tower with radio communication to their car. Cars that do not follow directives from Race Control via their spotter may be black flagged and removed from the event.

Waddell Communications www.waddellcommunications.com   860-573-8821

20E- 6.7.3 TRANSPONDERS – Transponder are required on the cars at all times. See the SMS General Rules for locating transponders properly. Any car not registering a transponder signal during practice may be black-flagged to be made aware of their scoring transponders failure and is required to remedy it before proceeding further in the event.

Mylaps America
32 Highlands Parkway Suite 104
Smyrna, GA 30082
Tel 678-816-4000

20E- 7 ENGINE COOLING SYSTEM – Only Water or SMS approved coolants or additives may be used in the cooling systems. Ethelyne Glycol or Propolyne Glycol coolants are not permitted. 

. A stock OEM type pump must be used. Electric pumps are not permitted.
D. Any serpentine, cog or V-belt pulley system is permitted.

20E- 8 ENGINE OIL SPECIFICATIONS – The use of combustion enhancing oils or additives is not permitted.

20E- 10 ENGINE DRIVE TRAIN – FLYWHEEL AND CLUTCH – The Quarter Master 298108 or 298158, 7-1/4” two disc V-Drive, with an SFI rated 153 tooth steel OEM type ring gear/flexplate that weighs a minimum of 4.1 pounds may be used in with the SK Spec Engine. Optional stock type clutch rule: A Stock OEM dimension 153 tooth steel flywheel and 10” steel clutch and pressure plate may be used. OEM type steel pressure plate and steel disc only. Solid type disc only, no paddle or button type discs. Minimum10″ clutch and pressure plate. Drilling or lightening of any part is not permitted. Steel bolts only. Flat surface machining allowed only on the face of the flywheel, any cutting on the back side of the flywheel will deem the part illegal. The following weights are the minimum allowed for each part:
Flywheel only (no bolts) – Non-Spec Motor     12.5 LBS.
Pressure plate, Cover, & Solid Disc (no bolts) 16 LBS.
The steel solid disc (no bolts) must maintain a minimum weight of 2.5 pounds and a maximum weight of 3.8 pounds after the combined weight has been determined.

20E- 10.3 BELL HOUSING – Only a commercially manufactured magnetic steel bell housing may be used. The bell housing must enclose the flywheel 360 degrees with minimum 3/16” inch magnetic steel. Any modifications you make to the bell housing must be done with 3/16” steel and welded in place (no bolt on pieces). A commercially manufactured bell housing (like the Quarter Master 008110440) with a bolt on bottom cover may be used. An opening no larger than 3 ½ x 4 inches may be used for throw out bearing access. This hole may be covered with sheet metal.

20E- 10.4 TRANSMISSION- The GM OEM production stock 3 or 4 speed transmission (top loader not permitted), Richmond two speed transmission (see approved part numbers below), or the Jerico 2SP (see approved part numbers below) transmission must be used.
A. All transmissions must have a constant engagement of the input shaft with gear and countershaft with cluster gears.
B. High gear must have a ratio of 1 to 1 and no other gear may have a ratio higher than 1.20 to 1.
C. The shifter and all of its components must be aluminum or steel.
D. Five-speed transmissions, with gears removed are not permitted. Quick change transmissions are not permitted.
E. Automatic or semi-automatic transmissions are not permitted.
F. Machining or lightening of any internal rotating or non-rotating parts including gears, shafts, and case are not permitted. Gun drilled transmission shafts are not permitted. Welding on any internal part is not permitted. Lightweight parts, machining, coatings, or special bearing upgrades are not permitted.
G. Additional or different from OEM bearings other than the tail-shaft, which may have roller bearings, are not permitted.
H. The transmission must be a “side shift” unit. Top shift transmissions are not permitted.

GM OEM Transmission-
OEM Stock cast iron, aluminum or magnesium transmission housings, or the Magnus part number MRPSA-1009 housing is permitted. The OEM Stock transmission side cover must be used. Removal of first gear or replacement of first gear with a metal spacer, in 4-speed transmissions is permitted. All other forward and reverse gears must be in working order, and they must be operational from inside the driver’s compartment. Only OEM type, steel, angle cut forward gears are permitted. OEM gear ratios must be used. Lightweight parts, machining, coatings, or special bearing upgrades are not permitted.

Richmond Two Speed-
Modification of the dog-ring and slider (high gear only) in Richmond 2-speed transmissions is permitted. The following Richmond 2-speed transmission part numbers are the only approved Richmond part numbers: 7020010X, 7020026X, 7027010X, 7027026X, the X representing Richmond’s ratios letter designator. The following Richmond produced low gear ratios are the only approved ratio for use in the Richmond 2-speed transmission: 1.2250, 1.3391, 1.4588, 1.5956, 1.7442. Lightweight parts, machining, coatings, or special bearing upgrades are not permitted.

Jerico 2SP-
The Jerico oval track 2speed transmission (part # 2SP, base model) as produced by Jerico is permitted.
The Jerico 2 speed transmission may be run, with only the following “Low Gear’ options allowed: 1.2250 to 1.7100, and “High Gear” must be 1:1. No modifications or options are allowed to the base Jerico 2SP.
The addition of any optional parts (other than base model supplied / needed), and/or any lightweight parts, machining, coatings, or special bearing upgrades are not permitted.

20E- 10.6 REAR AXLE
. Full floating magnetic steel double splined rear axles must be used.
B-1. All axles must be a minimum of 7.00 pounds while still maintaining a 1.250-inch manufactured outside shank size and a .6875-inch inside hole diameter.
E. Only magnetic steel axles, bearings, and axle housings are permitted.
F. Only one-piece, magnetic steel axles will be permitted. The axle splines must be straight cut, not crowned.  Crown type axle splines will not be permitted.
G. Cambered rear axle housings or other cambered components will not be permitted. A tolerance of 1½ degrees of camber (positive or negative) will be permitted.
H. Only aluminum or steel drive plates, the same thickness on the left and right side will be permitted. The drive flange splines must be straight cut, not crowned.
Only ten (10) inch ring gear and housings are permitted.
M. Thermal dispersant coatings are not permitted.

GEAR RULE – Quick Change rears must use a 4.11/4.12 (8/33 teeth), 4.57 (7/32 teeth), or 4.86 (7/34 teeth) 10” diameter ring & pinion gear set.
The 4.12 ring & pinion QC rear may use gear sets 25 (20/22), 12 (26/29), 7 (23/26), 7A (21/24), 17 (26/30), 17A (24/28) or 8A (23/27).
The 4.57 ring & pinion QC rear may use gear sets 1 (21/21), 2 (27/28), 5 (24/25), 15A (21/22) or 15 (19/20).
The 4.86 ring & pinion QC rear must use gear set 1, tooth count of 21/21.
Straight rears may use 4.86 maximum to 4.56 minimum, 10″ diameter ring & pinion.

SMS is aware of the 4.71 ring and pinion “shortage” and is currently reviewing the rule.

20E- 10.8 TIRES – Hoosier Tire East of Manchester, CT. is the sole tire supplier for the SK Modified Division. The approved compounds are Hoosier 27/13-15 M450 for right side tires and Hoosier 26/13-15 M30 for left side tires.  Tire purchases prior to the first scheduled race of the season may be made at Hoosier Tire East. After the first event of the season all tires used at SMS must be purchased at the track on race day. SMS Officials may confiscate and/or impound tires at any time for inspection. The JTR Eagle PPM tire chemical tester will be set at a fixed level and will be strictly enforced throughout the 2021 season.

Each tire will carry a special bar coded serial number. The legibility of the bar code is the sole responsibility of the team. Each SK driver will receive 13 tire credits at our opening event. Drivers must pick up their Tire Inventory card from the Handicapping / Sign in booth and enter the barcode serial number of the tires they wish to use. Each tire barcode that is entered on the tire sheet will use one of your credits. Drivers will receive two tire credits for each completed event (1 for completing the qualifying event, 1 for starting the feature event, EIRI). For events where pre-qualifying is in use, the driver will be awarded two tire credits for taking the green flag in the feature.
New drivers after our 4th event will get 8 tire credits for their opening inventory.
New drivers at our last event will get 8 tire credits, 4 for new and 4 for used spares.
The Tire Inventory card will have no more than 16 tires on it. Once you reach 16 tires you will have to remove tires from your inventory that you no longer need.
The Tire Inventory card will be filled out and turned in to the Tech Center each week prior to the scheduled drivers meeting. Drivers that do not turn in the Tire Inventory Card on time will be penalized. Edits to the tire inventory card after it is turned in is not permitted.
Drivers that have non-inventoried tires on their car during qualifying or feature events will be penalized.
In the event a driver changes cars for qualifying or feature racing, their tire inventory must accompany them to the new car (EIRI).
The amount of extra tires allowed for longer distance feature events will be determined by SMS Officials.
If a tire cannot be identified, it will be considered illegal.
SMS Officials may change or amend these rules at any time.

Minimum circumference of right rear tire @ 20 psi. is 84″.
F. Minimum Tire Pressures for all inspection purposes are ten (10) psi for both left side tires and fifteen (15) psi for both right side tires. Air may be added to the tires to achieve only the minimum tire pressures during inspections, per an SMS provided tire pressure gauge.

NOTICE: A participant competing in any race at SMS specifically agrees that he/she acknowledges it is illegal to soak or treat racing tires and that said soaking or treatment of racing tires is subject to suspension.

20E – 12.1 COIL SPRINGS – Only coil spring suspension will be permitted.  The suspension and coil springs at all four (4) wheels must be active and permit suspension movement in compression and rebound. All downward chassis movement while the race vehicle is in competition must be limited only by the normal increasing stiffness of the springs or the bottoming of the chassis against the race track, whichever occurs first. Any device or procedure that in the judgment of SMS Officials attempts to detract from or compromise the above will not be permitted, including “coil-bind”. Any type of chassis travel limiter, used in compression or rebound, will not be permitted. Front shocks must have a minimum of 2″ of piston available for spring travel in compression. All coil springs must not be colder than ambient temperature.

A maximum of two full (360 degree) non-adjustable spring rubbers in each coil over spring is permitted.

Shock/Coil over boots or bags are not permitted.

Coil Over Springs:
1. Coil over springs must mount to the lower A-frames.
2. Strut bars will not be permitted for mounting of coil over front springs.
3. Coil over springs must be manufactured from one solid piece of heavy-duty magnetic round steel (flat or oval wire is not permitted) and must be constructed with both coil ends closed and ground. One inactive coil on each end of the coil spring is permitted.
4. Only one (1) spring per wheel will be permitted.
5. Coil springs may be coated but coating thickness and material must be acceptable to SMS Officials.
6. All active coils of the spring must have the same coil spacing, same wire diameter, and same inside and outside diameter. The first and last coils may be different due to having closed and ground ends.
7. Progressive or digressive rate springs will not be permitted.
8. Front coil must be a minimum of 6” in free height and a minimum of 250 lbs. per inch of spring rate.  Rear coil must be a minimum of 8” in free height.

20E – 12.2 SWAY BARS (ANTI-ROLL BARS) Front sway bar(s), when used, must be for the purpose of anti-roll only. The front sway bar must freely rotate in its mounts. The movement of the front sway bar arms must not be prevented or restricted beyond that of normal use as an anti-roll bar.
A. Only magnetic steel front sway bars will be permitted.
B. Rear sway bars (anti-roll bars) will not be permitted.
SMS reserves the right to set and enforce a maximum sway bar spring rate.

20E- 12.3 COIL OVER SHOCKS – Shock must be non-adjustable or single adjustable (rebound adjustable or gas pressure adjustable, as determined by SMS Officials), available to all competitors “race ready” with a published price of $440 or less ready to race, less any separate coil-over kits.

The following shocks  are permitted for competition in 2021:
AMF – SK Mod Series
Bilstein – ASN Series, AS2 Series, or XVA Series
Genesis – G1 or G0 Series
Integra – 310 45650SNSV-SK or 310 45670SNSV-SK Avenger Series
JRI – 200-426 or 200-427
Koni – 30 Series
Penske – 7500 series or 7150 series
Pro – AC series
QA-1 – 62 Series

Shocks will be disassembled and dyno’d for inspection and comparison. Shocks must be used as they are purchased, with all factory supplied valving and components for the model number used. Any other shock must be submitted to SMS for approval (the parts approval process is described on the first page of the rules). Any submitted shock must be single adjustable, available to all competitors “race ready” with a published price of $440 or less ready to race, less any separate coil-over kits. All shocks subject to SMS Officials’ approval.

20E- 12.5 SPINDLES, WHEEL BEARINGS and HUBS – Front spindles must be linked to frame utilizing two individual tethers per spindle. All tethers and their installation must be acceptable to SMS Officials. Low drag components (excluding seals) are not permitted. The use of oil filled hubs, oiled bearings, low friction bearings, non-steel bearings, coated or polished spindles, bearings or races will not be permitted. Two standard steel wheel bearings, a wheel bearing seal, a torque nut and a standard nut locking mechanism are the only components permitted on each spindle/hub assembly.
E. Oil filling of any spindles, wheel bearings or hubs is not permitted.

All cars must maintain the following track width requirements. A minimum front and rear track width of 82 inches and a maximum track width of 83-3/4 inches will be permitted. The track width will be determined by measuring the left outside wheel (rim) bead surface to the right outside wheel (rim) bead surface at spindle height.
B. Aluminum or steel spacers will be permitted to utilize the maximum allowable track width. Spacers must be acceptable to SMS Officials.

20E- 12.8.2 GROUND CLEARANCE REQUIREMENTS – The frame rail and sheet metal ground clearance will be a minimum of two (2) inches. All ground clearance requirements will be measured with the driver in the car.

Four wheel disc brakes are mandatory. Only magnetic cast iron or cast steel round circular rotors permitted. Only metal brake calipers will be permitted. Drilled, slotted or grooved rotors are not permitted. Only factory dust cleanouts are permitted. Dust cleanouts should not exceed .038 in depth. If the dust cleanout exceeds .038 in depth, the rotor may be deemed illegal. The brake rotors must be bolted directly to the hubs. Floating brake rotors will not be permitted.
B. Only Single stage master cylinders are permitted. All brake components are subject to SMS Officials approval.

20E- 14.2 – BRAKE COOLING Electric blowers are not permitted for cooling purposes in brake duct systems. Additionally, electric blowers are not permitted anywhere on the car for cooling (i.e. brakes, rear end, etc.).

20E- 15 FUEL SPECIFICATIONS – The only approved fuel for any SK engine is Sunoco Supreme. Sunoco Supreme is available at Stafford Motor Speedway.
A. Icing or cooling of the fuel system is not permitted in the paddock, pit or racing area.
B. Gasoline may be tested and certified at any event through the application of various chemical analyses as considered appropriate by SMS Officials. Gasoline may be checked before, during and after the racing events.
C. Nothing may be placed in the fuel line other than a standard fuel filter. The use of any type of fuel catalyst or other fuel-altering devices is prohibited.

20E- 16 FUEL SYSTEM – See NWMT rulebook

20E- 16.1 FUEL CELL – Must meet NASCAR specifications with a fuel cell bladder made of a material that returns to its original size and shape after deformation. Rotational molded bladders are not permitted. It is highly recommended that the fuel cell bladder be no more than six (6) years old. Competitor must provide bladder model, serial number and date(s) to SMS Officials before competing. If a gas cap is used it must be painted white with the car number on it for identification. For additional specifications see the NASCAR rulebook. The minimum requirement for approved fuel cells at SMS are as follows: ATL Super Cell “100″ FB1 – Series Bladders. (Note: the complete cell will be the SU1- Series), and the Fuel Safe Sportsman Cell (SM Series). Any cell that is rated above these cells (ATL 200 & 500 series), and the Fuel Safe Pro Cell (PC Series), will also be approved for competition at SMS. For additional specifications see the NWMT rulebook.

20E- 16.2 FUEL CELL CONTAINER – Fuel cell container must be RED. See NWMT rulebook.

20E- 16.5.3 FUEL SHUT-OFF – A 1/4-turn fuel shut-off valve of minimum 3/8-inch NPT with minimum 4-inch handle is required in the fuel line. The fuel shut-off valve must be located 8-inches inboard of the passenger side frame rail’s outside edge and 24-inches forward of the main roll bar (#1 bar). The fuel shut-off valve must be mounted securely to the underside of the driver’s compartment sheet metal. The fuel shut-off valve shank must protrude through a maximum 1-inch diameter hole in the sheet metal to the interior of the driver’s compartment. The fuel shut-off valve handle must be parallel with the sheet metal that the valve is mounted to. The fuel shut-off valve handle must be a minimum of 4-inches in length, red in color with a minimum of 1-inch clearance from the sheet metal throughout its full travel. A minimum 6-inch by 6-inch square area must be painted white with the fuel shut-off valves’ ON and OFF positions clearly labeled with 1/2-inch tall, black in color lettering. The shut-off valve must rotate clockwise from a ON position with the handle parallel with the frame rail, pointing towards the rear of the car, to the OFF position with the handle perpendicular to the frame rail pointing toward the driver.

NOTICE – Competitors are solely and directly responsible for the safely of their race cars and racing equipment and are obligated to perform their duties (whether as a car owner driver or crew members) in a manner designed to minimize to the degree possible the risk of injury to themselves and others.

CONTINGENCIES – Contingencies are a valuable part of the SMS program. Contingency stickers must be displayed for either product or monetary considerations. Each division will be notified as to what stickers are required. To be eligible for contingency rewards the stickers must be displayed on both sides of the car in such a manner as to be clearly visible in a photograph.

20E – 18 ROLL BARS – (8) – (A) The door bars (#9 A & B), on both the left and right sides, must have a minimum of four (4) bars equally spaced from top to bottom that must be welded horizontally between the vertical uprights of the main roll bar (#1) and the front roll bar legs (#2 A & B). The top door bar on each side must maintain a minimum vertical height of 15-1/2 inches from the top of the main frame rails to its centerline and match up with the intersection of the dash panel bar (#8) at the roll bar legs (#2A & #2B) at the front and the intersection of the horizontal shoulder bar (#7) at the main roll bar (#1) at the rear. All door bars must be convex in shape. The door bars (#9 A & B) must have a minimum of six (6) vertical supports per side with two (2) equally spaced between each door bar. These supports must be made from a minimum of 1-3/4 inches by 0.090 inch wall thickness magnetic steel seamless round tubing (not numbered but shown in the left side view of diagram #3). Right side door bars must cover a minimum of 25 inches of door length and may be either four (4) horizontal bars with six (6) vertical studs or two (2) horizontal bars and two (2) bars configured in an X design. If the X design is used, a vertical bar must connect through the center of the X from the top horizontal bar to the frame.

(B) A 13 gage (0.0897 inch thick) magnetic steel anti-intrusion plate(s) must be securely welded to the outside of the left side door bars. The anti-intrusion plate(s) must fill the area between the horizontal centerlines of the top and bottom door bars, and vertical centerlines of main roll bar (#1), and the left front roll bar leg (#2A). The plate(s) must be formed to match the curvature of the door bars. Plate(s) welded between the vertical upright bars should be as large as possible. All plate(s) must have the corners welded with one (1) inch of weld followed by a maximum of three (3) inches of surface not welded and followed again by a minimum one (1) inch weld. To facilitate emergency removal of the left side door bars (#9A), the anti-intrusion plate must have six (6), 2-1/8 inch diameter holes cut in the anti-intrusion plate, with three (3) holes forward of the front vertical supports and three (3) holes rearward of the rear vertical supports in the following locations: The upper two (2) holes must be centered vertically between the left side door bars (#9A-1&2), at an on-center distance of three (3) inches from the center of the front vertical support and the rear vertical support. The middle two (2) holes must be centered vertically between the left side door bars (#9A-2&3), at an on-center distance of three (3) inches from the center of the front vertical support and the rear vertical support. The lower two (2) holes must be centered vertically between the left side door bars (#9A-3&4), at an on-center distance of three (3) inches from the center of the front vertical support and the rear vertical support (see Diagram #9A, in the rear pages of the rulebook).

(9) All cars must have a foot protection bar acceptable to SMS Officials installed on the left side of the roll cage. The foot protection bar must be located at or in front of the pedal assembly, when viewed from the side and above. The foot protection bar must be completely welded to the left front roll bar leg (#2A) and extend forward and be completely welded to the main frame rail or front sub-frame.


LUDLOW, MA 01056
Don Wood
Tony Alteri
Billy Mathes
Mike Pettit
GROTON, CT 06340                                          
Gary Espinosa
Bill Carlquist
Peter Chillemi
Dave Miller
Andy Krawiec
Brian Kowalshyn