2018 Thunder Four Rules

Thunder Fours continue to be an exciting division of Saturday night racing at Wiscasset Speedway!  An entry level into racing, the objective of Thunder Fours is to provide a fun, economical and safe racing experience for the novice driver as well as the more experienced driver who enjoys the challenge and affordability of pure stock four-cylinder racing.  The following rules are a continued effort by division participants working together for division growth with respect to car variations, affordability, and fairness of competition. While we understand these rules may not perfect and may not encompass all cars, we request they not be interpreted as opportunities to cheat and/or discover loopholes to gain an advantage.  We shall always welcome and work to accommodate all who respectfully meet the spirit of the rules and desire to join us racing at Wiscasset Speedway.  Exciting, challenging and lots of fun, Thunder Fours is the perfect opportunity to live the dream of learning how to prepare and race your very own car – without having to spend lots of money!

2/26/18 – Updates, Clarifications, Omissions re: Drive Train Exceptions #1 and Wheels-Brakes-Tires #2

12/1/17 – Rules Set.  In regards to tunable vs non-tunable chipped ecus, further study will be held as the season gets underway to effort to prove or disprove the various thoughts, theories & opinions.


DRIVER SAFETY REQUIREMENTS – drivers must wear the following required items at all times while on the racing surface. 

  1. One or two piece long sleeve SFI approved fire resistant suit in good condition and free of rips, tears or holes.
  2. Fire resistant shoes and gloves.
  3. Helmet must meet or exceed the Snell 2010 standard.
  4. Face shield, glasses or goggles.

Highly Recommended & Encouraged not yet required but you know it’s coming 😊

  1. Head and neck support/restraint safety device.

Recommended not required

  1. Fire resistant underwear, socks, and head stocking.


  1. Cars must be powered by a stock fuel injected or carbureted 4-cylinder engine that is stock for the year, make, and model car that it is being used in. Compact trucks are not permitted.
  2. Foreign & Domestic four (4) cylinder, four (4) passenger, front engine, front or rear wheel drive only
  3. Four (4) wheel drive models can be converted to front wheel drive with an assessed fifty (50) pound weight penalty.


  1. Minimum roll cage tubing specification 1½ inch x .095 inch DOM or seamless tubing. In the interest of safety, water tubing, exhaust tubing, etc. is unacceptable.
  2. Minimum four (4) point roll cage is required. In addition to the required four (4) point roll cage, the structure may extend to the front as far as the radiator support and to the rear to sufficiently protect the fuel cell.  Left side must have a minimum of three (3) horizontal bars with spacers.  Right side must have a minimum of three (3) horizontal bars with spacers or and “X” and two (2) horizontal bars.
  3. A minimum of sixteen (16) gauge steel plate of sufficient length and width as to protect the driver must be welded to the roll cage.
  4. Any bar within the drivers reach must be padded with an approved product. Pipe insulation will not be acceptable.
  5. Front and rear firewall must be completely sealed from the driver compartment with sheet steel similar in thickness to existing car structure and securely welded.
  6. All welds are to be of high quality and must completely surround the joint. Absolutely no butt welds or sharp edges anywhere.
  7. Stock column must be retained. Steering wheel may be replaced with a removable made for racing unit. All steering wheels must have a center pad.
  8. Maximum eight (8) gallon fuel cell, in a steel container with a check/rollover valve in the vent line; secured with two (2) straps front to rear and two (2) straps left to right. The minimum dimension of strap material is 1/8 inch x 1½ inch. Fuel cell may not be offset.
  9. All fuel filters must be of metal construction. No plastic, glass or other material will be allowed.
  10. Any line containing a combustible material must be steel and routed outside of the driver compartment.
  11. Electric fuel pumps must be wired through a low oil pressure cut off switch.
  12. Five point quick release harness system in good condition mounted with 3/8 inch bolts minimum Grade eight (8), washers and locking nuts.  These must be attached at two (2) separate points on the frame, equal distance from the seat back and not less than twelve (12) inches apart.  (See manufacturer instructions for details).  Sternum belts are highly recommended.
  13. Aluminum racing seat with right and left head supports. Seat must be mounted and attached securely to the cage. A support brace must be installed at the rear of the seat.
  14. Racing regulation window net with quick release attachment required to be securely installed on driver side window. Plastic, plastic brackets, tape, wire or any other makeshift window net creation and/or mounting devices will not be acceptable.  Window nets must be securely fastened at all times when car is on racing surface.
  15. Minimum three (3) pound fire extinguisher mounted with quick release metal bracket within reach of driver when belted in. Extinguisher must be operational with full gauge reading.  Plastic brackets, tape, wire or other makeshift mounting devices will not be acceptable.


  1. All body components must be original equipment without modification except to accommodate roll cage installation, fuel cell installation and tire clearance. Replacement of rocker panels allowed attach and turn strait in – no kickout, flares, etc. No made for racing body parts.
  2. Hood and deck lids must have all bracing removed and be tethered to the car.
  3. Sun roof must be covered with sheet steel of similar thickness to existing roof structure and welded into place. No convertibles or “T” tops.
  4. Original equipment windshield (safety glass) in good condition may be used. Minimum eighth inch (1/8”) Lexan windshield is allowed with at least one (1) support strap installed close to center. All other glass and combustible material must be completely removed.
  5. One (1) inside mirror no larger than three (3) inches x twelve (12) inches and one (1) left side mounted mirror no larger than five (5) inches x five (5) inches is allowed.
  6. Bumpers are required to have a retention chain/cable at both ends.
  7. Rub rails mounted tight against the body are allowed.
  8. Lifting/towing chains or cables must be installed both at the front and the rear of the race car are required. Absolutely No Exception. 


  1. Any radiator that fits under the stock hood is allowed.
  2. Water and a cooling additive only. No antifreeze allowed.
  3. Must have a minimum one (1) quart capacity sealed overflow container.
  4. Car must not have fluid leaks of any kind.
  5. No forced air induction (turbocharger/supercharger) allowed.
  6. Battery may be relocated within the confines of driver compartment. Battery must be in a sealed battery box and properly secured.
  7. Exhaust system with a muffler is required and must extend past the drivers compartment turning down toward the ground with the end of exhaust system under the race car, not out the side or the rear of the race car.


  1. All aspects of the drive train and support systems must remain as produced by the manufacturer.
  2. Car must have functional reverse gear.
  3. Driveshaft must be painted white.
  4. Driveshaft loop required near the front of the driveshaft with material specification minimum of one quarter (¼) inch x two (2) inch. Rear driveshaft loop is recommended.


  1. CRX allowed single overhead cam only.
  2. Open differential only.


  1. Minimum ride height is five (5) inches with driver.
  2. Track Width shall be sixty-four (64) inches maximum measuring from center to center.
  3. Spring diameter must be same as original equipment.
  4. Springs may be cut or heated to obtain ride height. No Racing Springs.
  5. Springs must be the same wire size, coil count and height side to side.
  6. Spring rubbers or twist in boosters are allowed and must be safety wired to spring.
  7. No suspension travel limiting devises of any kind. If original equipment, they must be removed.
  8. Up to one half (½) inch rear camber either positive or negative allowed. No tolerance +/-.   No excuses.  Camber will be measured on the rim.
  9. Front strut towers may be ground/drilled for camber/caster adjustment but strut towers must not be moved.
  10. Spindles may be ground/drilled for camber adjustment leaving enough material to stand the rigors of racing.
  11. Bending of suspension parts is not allowed.
  12. Sway bar may be made adjustable at one point only.
  13. Only commonly available shock absorbers/struts allowed – ie – NAPA, Car Quest, O’Reilly, etc. No painting or altering these items in any way.  No Bilstein, Carerra, Pro, Afco or otherwise unit from a performance manufacturer.


  1. Steel wheels required for all cars.
  2. Maximum seven (7) inches inside bead to bead.
  3. All four wheels must be the same diameter and width. Backspace optional.
  4. Every wheel must have all wheel studs with required one (1) inch lug nuts.
  5. All four wheels must have brakes in good condition. No bias adjusters.
  6. Commonly available DOT approved radial tires and Legend take off (used) tires will be allowed.
  7. No retreads of any kind.
  8. No “V” rated or otherwise high performance tires.
  9. All four tires must be the same aspect ratio – ie – four 60 series or four 65 series.
  10. No restriction on numerical value -165,185,195,205, etc.
  11. Minimum tread wear 300.
  12. To Aid Tech Inspection – size and tread wear must be marked with a white or yellow paint marker.
  13. All cars are subject to random testing at the discretion of Tech, durometer testing will be conducted On Track after heats and features of the top five (5) cars. Failure to meet the 2018 division preset number (Right Sides (TBA) and Left Sides (TBA) with No Allowances) will be subject to penalty as follows: Heats – illegal tire(s) held at Tech for the remainder of the race event and not allowed again until cleared by Tech; forfeiture of heat points and feature start is rear of the field.  Features – Full DQ with illegal tire(s) not allowed again until cleared by Tech.
  14. While division participants agree use of tire conditioning agents is difficult to police – all agree application of such will not be allowed at the track.


High octane racing fuel is permitted, although not encouraged or recommended.  Any standard quality street-pump fuel is fully satisfactory saving unnecessary and excessive fuel expense. 


  1. Car weights are race ready, full of fuel and with driver in the seat.
  2. One (1) pound per cc – minimum of two thousand (2000) pounds.
  3. Left side maximum is fifty four percent (54%) post race.
  4. All ballast weight must be located outside of the driver compartment with each piece attached with a minimum of two (2) 3/8 inch bolts, washers and locking nuts.
  5. All weight must be lead with each piece painted white and display car number.


  1. Dual overhead cam engine……………………………+50 lbs.
  2. Four wheel drive converted to two wheel drive………+50 lbs.
  3. Twin cam Honda engine………………………………+100 lbs


  1. All car numbers are assigned and registered by Wiscasset Speedway.
  2. When changing divisions, a new number will be assigned.
  3. Car numbers must be a minimum of eighteen (18″) inches high and three (3”) inches wide.
  4. Numbers shall be painted in contrasting colors to the car on both doors and the roof. Reflective chrome, gold or prism numbers will not be acceptable.
  5. Roof numbers should be visible as read from the grandstand side of the car. The car number must appear in 6″ high numbers in the uppermost corner of the windshield on the passenger side and also on the right rear.


  1. Two way communications shall be allowed; however, Wiscasset Speedway Management will require frequency registration.
  2. RaceCeivers are mandatory equipment.

All race car components, including sealed engines, may be subject to teardown/dismantle inspection at any time.   Refer to General Rules – Tech Information Section. 

DISCLAIMER:  Motorsports At All Levels Pose A Risk To Your Well Being. Following The Rules Set Forth By Wiscasset Speedway In No Way Guarantees Or Suggests Your Safety.

Wiscasset Speedway Reserves The Right To Modify This Document At Any Time.  Such Modifications Will Become Effective And Enforced On The Next Race Date.

Last Edit 2/26/18

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