Irwindale Spec Late Models – 2021


2021 Irwindale Speedway Spec Late Model Rules


The intent of this racing series/division and its rules are to create and maintain a safe, competitive, and affordable racecar. The basis of this racing series is that the race car, parts and all components remain unchanged. If you are interested in working on your race car to help the car’s performance by making modifications to other than the minimal set up options you have, then this series is not meant for you. If this rule book does not specifically say that you can change/modify/add something, then you must consider that the change/modification/addition is illegal. All components must remain the same as delivered by Racecar Factory.


Air Cleaner

  1. Standard metal housing
  2. Air filter element must be 4” X 14”.
  3. No air diverters, shields or coatings


  1. Only a lead cell or gel cell battery must be
  2. Minimum dimensions are 6” wide x 10” long x 7”
  3. Car must run 12-volt electrical
  4. Battery must remain in its stock location and securely
  5. The original stock battery bracket may not be altered or


  1. The only approved body is the Five Star S2 Sportsman
  2. All panels must be run as produced by Five Star Race Car
  3. Body must remain mounted to original body specifications and
  4. Body must fit Fivestar/RCF template
  5. A-post windows must be 10” long
  6. No excessive trimming of body
  7. Maximum front nose splitter width cannot exceed 75”.
  8. Body mounts and bumpers must be run as supplied by


  1. All brake parts must remain stock size, shape, weight and
  2. Front and rear brake calipers must be stock GM replacement
  3. Brakes must be operational on all four
  4. No proportioning valves allowed. One brake bias adjuster
  5. Only magnetic steel brake rotors
  6. Brake rotors must be minimum .900 x 11.75” front, minimum .800 x 11.75”
  7. Brake rotor must be vented
  8. No drilled or scalloped brake rotors
  9. Master cylinders must be Wilwood 260-6765 and 260-6766.
  10. Brake cooling fans, brake ducts or holes in nose are not allowed


  1. Holley 3310C is the only approved
  2. Primary jets and power valve may be replaced with OEM
  3. Choke flap and linkage mechanism must be removed
  4. No other modifications
  5. Secondary diaphragm spring must remain
  6. External vacuum ports must be
  7. Carburetor is subject to exchange by tech


  1. Absolutely no modifications of the chassis will be
  2. Chassis must be raced as produced by
  3. No altering pick up points or mounts on

Clutch and Flywheel


  1. Flywheel must be 153 tooth OEM magnetic steel only (minimum 15#).
  2. Clutch disc must be magnetic steel (minimum 5#).
  3. Pressure plate must be magnetic steel (minimum 13#).
  4. 4” stock single disc diaphragm clutch only.
  5. Clutch master cylinder must be a Wilwood 260-1304.


  1. One electric fan must be
  2. Radiator ducting must be flat panels, no wider than the radiator, and seal to

Driver Seat

  1. Seat must be from a recognized manufacturer of seat and safety
  2. Seat construction must be solid aluminum, fully padded, with padded pelvis and left and right side shoulder
  3. Seat must have a head restraint system, either integrated in the seat or a bolt-on
  4. Seat must attach to chassis at six points w/3/8” grade 8

Driver Uniform

  1. Must be a multi-layer, full-coverage, Nomex-type fire protectant uniform meeting rated SFI-3 or better specifications.
  2. Nomex-type gloves, socks and racing shoes are
  3. Nomex-type fire protectant underwear is recommended. Soiled, torn, worn, or poorly fitting uniforms will not be


  1. Must be 2.75” x .060 magnetic steel
  2. Must have solid tube
  3. Must use magnetic steel u-joints.
  4. Driveshaft must be painted
  5. Minimum weight of driveshaft is 14#.


  1. GM 88958602 factory sealed break-away bolt engine
  2. All engine components must be stock GM only including valve springs, rocker arms and
  3. No heat shields allowed on valve covers.
  4. After an engine has won three main events in one season, that engine may be purchased by any registered RCF Spec Late Model race team that is in the top ten in the current point standings at the conclusion of an event. Price will be current retail price plus 10%.

Engine Mounts

  1. Engine must be centered in
  2. Minimum crankshaft height is 6 1/4” from top of cross member to center of

Exhaust System

  1. Exhaust system, headers and tail pipe must remain
  2. Exhaust components may not be altered in any
  3. Exhaust can’t stick out past the body.
  4. No header wrap allowed on exhaust or
  5. Exhaust system may be painted with high heat
  6. Exhaust system cannot be ceramic
  7. No grinding on headers or header

Fire Control

  1. Fully-charged 5# fire suppression system containing DuPont FE-36 or equivalent is
  2. Fully charged 10# or 13# dry chemical, Halon, or equivalent fire extinguisher is recommended in each entrant’s garage or pit

Front Suspension

  1. All front suspension parts must remain stock, size, and weight as delivered by
  2. No altering of suspension
  3. Upper and lower ball joints must be
  4. Low friction ball joints are not


  1. Lower and Upper A-arms must remain
  2. Left front upper A-arm must be 5”.
  3. Right front upper A-arm must be 9”.
  4. No slotted or bearing cross shafts
  5. Spindles must be
  6. Front hubs cannot be lightened or
  7. Strut tubes may be aluminum hex or
  8. Tie rod tubes must be aluminum hex
  9. Steering box must be a GM Saginaw 12 to 1 ratio
  10. All rod ends must be magnetic

Fuel and Fuel Cell

  1. Standard gas station Pump Gas
  2. No mixing of fuel or fuel additives
  3. Fuel cell must remain securely mounted in stock
  4. Fuel cell must be vented to rear bumper
  5. Fuel cell must have a ground strap from fuel cell ring to the
  6. No cooling of fuel at any
  7. Fuel line must be steel braided or black braided


  1. All nuts and bolts must be solid magnetic steel


  1. All heights will be checked with driver in race
  2. Nose Height: minimum 5”.
  3. Side Skirt Height: minimum 25”.
  4. Frame Height: minimum 5”.
  5. Rear Quarter Panel at Tail and Deck lid: maximum 36”.


  1. Stock GM HEI Distributor
  2. Ignition module must remain
  3. No billet distributors
  4. Stock GM distributor cap, rotor and coil
  5. No heat shields allowed on

No Push Rule

  1. A) Cars must be driven to Tech and from Tech to staging area for Qualifying.

Number & Decals

  1. Must have readable numbers on door panels and roof. Numbers on door panels and roof must be minimum 20 inches in height. Roof numbers must be readable from the passenger side of the car. Numbers of minimum 5 inches in height must be applied to the right front bumper and left rear bumper areas of the
  2. Series sponsor decal must be displayed across front
  3. Front fenders reserved for series contingency sponsors. Contingency sponsor decals must be placed in line with and forward of the “A”


  1. Two way radios between driver and crew are required when car is on the
  2. Each team must monitor race control during practice, qualifying and
  3. Spotter must be in designated area at all times while car is on
  4. Team radio frequency must be registered with the

Rear End

  1. Full floater rear end with minimum .188 axle tubes
  2. Ford 9” mini spool
  3. Rear gear ratio must be 56.
  4. No lightening or back cutting of


  1. No lightweight yokes
  2. Solid magnetic steel axles only. (Minimum diameter 200”)
  3. No cambered rear end housing.

Rear Suspension

  1. All suspension mounts and pick up points must remain
  2. All trailing arm tubes must be aluminum hex
  3. Track bar hex tube must be 25 3/4″ minimum length and both rod ends must have jam
  4. All rod ends must be magnetic steel 3/4”
  5. No quick adjusters allowed on track bar or top
  6. Brackets on rear end housing may not be moved or

Rear Spoiler

  1. The rear spoiler must be mounted in original
  2. The rear spoiler must be mounted center on tail with 1/2″ gap at center between blades.
  3. Spoiler size is 6″ X 59″ with notch in 5” tall x 60” maximum width with ½” slot in center.
  4. Rear spoiler must be mounted with approved 70 degree

Seat Belts, Shoulder Harness, Window Net

  1. Must be 5-point or 6-point SFI 16.1 or 16.5 rated, display a valid label, and dated within 3
  2. Seat belt system (seat belt, shoulder harness, crotch belt) must connect at the lap belt with a quick release buckle for a one-handed, gloved release of all belts in all conditions. It must be either a latch link & lever or cam lock
  3. Lap belts must be 3” wide. Shoulder harness may be 2” wide over HANS
  4. Center crotch belt must be securely mounted to the lower seat frame at the
  5. Where the belts pass through the seat edges, it must have a grommet installed, be rolled, and/or padded to prevent cutting of the
  6. Window net must be SFI 27.1 rated, display a valid label, and dated within 5


  1. Shock numbers must remain stamped on shock, Must use the following approved shocks: 1. 310-42173/5 LR
  2. 310-42174 RR
  3. 310-42175 RF
  4. 310-42174/6 LF


  1. Coil over springs must be 2.5” ID x 14” tall. Only the right rear spring may be 12”
  2. No barrel
  3. Minimum front spring rate 200#.
  4. Maximum rear spring rate 500#.
  5. Only 1 spring per shock
  6. Only 1 spring rubber per spring
  7. Bump stops are not

Sway Bar

  1. One piece 1.25” sway bar
  2. Sway bar mounts must remain stock as produced by
  3. No quick adjusters
  4. Sway bar must attach to right side lower shock mount
  5. Left side sway bar must run on slapper
  6. All sway bar components must be magnetic

Technical Inspection

  1. All cars and drivers must go through and pass inspection prior to
  2. After each Main Event, the top three finishing cars must report directly to tech


  1. Hoosier 970 Tire


  1. Each car with be allowed 5 branded tires at their first race.
  2. At each race event they will allotted 1 branded tire per
  3. No other tires will be allowed for
  4. You may practice on any 970
  5. No chemically altered
  6. Tires must remain as manufactured. No shaving, grinding, or grooving of tires
  7. Tires serial number will be recorded by Irwindale Official for

Track Width

  1. Front must be 63” maximum from center of tire to center of tire at spindle
  2. Rear must be 62.5” from center of tire to center of
  3. No wheel spacers


  1. Must be magnetic
  2. Must be 3 speed
  3. Stock OEM transmission with three forward and one reverse
  4. Transmission cannot be lightened or
  5. Transmission must weigh 75 pounds without shifter. No polishing or coating internal
  6. Transmission mount must be rubber or urethane


  1. All cars must have an operating transponder for the entire
  2. Must be mounted vertically 24” behind the centerline of the rear axle housing on the right side frame rail.
  3. Teams who own transponders may use them and must register them with the track officials. Teams may elect to rent transponders from the track.


  1. Minimum weight 2,800 lbs with driver prior to main
  2. All weight includes car and driver, race ready with all fluids and safety equipment on
  3. All weight must be in left side rail (3” x 4” tube) or inside the center section frame rails on right or left sides (2″x 3″).
  4. Weight must be stationary and secured by 3/8″ grade 8 bolts at each end of the frame
  5. All weight must be non-magnetic lead; no tungsten or other
  6. All weight must be painted white with car
  7. No weight may be added to or clamped to the chassis anywhere else but the described
  8. Maximum left side weight before event with driver is 55%.


  1. Wheelbase must be 108” +/- half
  2. Wheelbase must be within 1⁄2” from side to side


  1. Circle Racing Wheel 15” x 8” steel wheel
  2. Wheel must be 4” backspace
  3. Minimum weight of wheel is 19#.
  4. Lug nuts must be 5/8”-11 threads with a 1” hex outer
  5. No gun drilled wheel


  1. Drivers must wear a full-face helmet with one of the following certification labels: Snell SA 2005, Snell SA 2010, FIA 8860-2004, FIA 8860-2010, or SFI31.1/2005. SFI or Snell certification label must be visible for inspection. Any helmet with the labels defaced, obliterated or removed will not be approved
  2. “M” rated helmets not
  3. Eye protection is mandatory at all
  4. Helmets showing wear or abuse, such as chipping or cracking, will not be
  5. Head and Neck Restraint Devices/Systems mandatory.


  1. Drivers must connect their helmet to a head and neck restraint device/system at all times during an Event (practice, qualifying and competition).
  2. Must meet SFI 38.1 specification and must display a valid SFI 38.1
  3. Device/system must conform to the manufacturer’s mounting instructions, and must be configured, maintained and used in accordance with the manufacturer’s