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General Rules
Plymouth Speedway Rules
Plymouth Speedway General Rules - All Classes
General Satety Rules - All Classes
On Track General Rules
Pit Area General Rules
Nitro Crash - O - Rama Rules
Individual Class Rules
Modifieds
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Pure Thunder Stock
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Pure Thunder Stock Rules
 
All drivers are required to have their own Raceivers for one-way communication with race director official.
Top 5 feature finishers will be required to go to tech area after the race.
 
General
1. Inspections may occur anytime at the discretion of a race official.
2. All cars must be strictly stock for make and model of car from front bumper to rear bumper. Minimum wheelbase of 107”.
 
Weight
1. 3200lbs with driver
2. Ballast allowed but must be attached with two 1/2" bolts. Ballast not allowed in driver's compartment. Ballast must be painted white with car number and must meet safety rules contained herein.
 
Frame and Roll Cage
1. Complete bumper-to-bumper OES stock frame for make and model of car. 2"x 3" framing may be used from stock rear shock mount (rear kick up) to rear bumper. "2 x 3" framing MUST appear in stock location. Cars with actual stock rear subs, 2"x 3" bar bracing may be used but still must retain stock appearance.
2. No Unibody cars. Unibody cars that have been welded to create full frame car not permitted. No Camaros.
3. 107” minimum wheel base.
4. Rust spots may be repaired.
5. Any repairs to front stub must retain exact OEM measurements for make and model of car. These repairs are subject to track official approval.
6. No switching or shifting of any body part or frame.
7. Roll cage must be composed of a minimum 1 ½” OD .090 thickness round steel tubing.
8. A four-post roll cage must be installed with minimum 3 door bars on driver’s door. Driver’s door must have 1/8” steel plate welded.
9. Minimum 2 bars for passenger side door.
10. Bars may be added from firewall forward to protect frame and radiator.
11. Main roll cage can be braced rearward to the kick up of the rear frame.
12. Drive shaft hoop is mandatory and must be installed 6-8” behind transmission tail shaft. No chains allowed.
 
Body
1. Stock OEM steel body only. No aluminum body pieces allowed. Stock steel body must match make and model of car in OEM location. No switching or shifting of any body parts.
2. Stock steel unaltered floor pan.
3. Stock front firewall in stock location.
4. Complete firewall must seal trunk from driver’s compartment. 16 gauge sheet metal minimum.
5. The only allowable modifications to the floor pan or firewall is to repair rust holes. All holes within driver’s compartment must be covered with 16 gauge sheet metal.
6. All inner body panels must be unaltered except doors for roll cage bars.
7. Hood and trunk must be securely fastened with hood pins or similar.
8. All doors and body panels will be welded together.
9. A fuel cell is mandatory. No stock gas tanks allowed. Fuel cell must be mounted in trunk area between frame rails. Fuel cell must be above center line of rear end differential housing or 12” above ground, whichever is highest. For more specific detail, see Fuel Cell Installation section.
10. Trunk floor may be cut to accommodate fuel cell. Minimum of two, 12 gauge 1 ½ inch safety straps.
11. No spoilers allowed.
12. Stock looking plastic front nose pieces allowed. Stock appearing rear bumper covers allowed. Stock style rear and front bumpers mandatory.
13. Stock style bumper will be securely fastened in place in stock location welded to frame rails. No front or rear bumper shocks allowed.
14. Front fender wells may be removed.
 
Windshield and Glass
1. All glass, headlights, tail lights must be removed prior to arrival at the track.
2. No broken glass shall be in the car. Car must be swept clean.
3. 4 bars minimum in front of driver in window. Bars must be 3/8” minimum with wire mesh fastened.
 
Suspension
1. OES stock suspension only for make and model of car.
2. Lower A-arms must be OEM stock for make and model. No aftermarket ball joints. Front upper A-arms may be non-adjustable tubular steel in stock location. No welding or altering of upper A-arms allowed.
3. Rear suspension arms must be OEM stock for make and model. No aftermarket rear suspension arms permitted.
4. Stock steering box. Stock pitman arm. Stock center link. Stock tie rod ends. Heim joint style tie rod ends/steering linkage not permitted.
5. No coil over, overload, cargo ratchet or air assisted shocks permitted.
6. No racing shocks permitted. Steel shocks only. Shocks must maintain stock OEM for front and rear for make and model and in stock location.
7. Racing springs allowed. Must maintain stock OEM frame and body heights for make and model of car.
8. Metric cars may reinforce OEM upper A-frames only.
9. No lift bars or recovery shocks or spring recoils. Stock shocks only.
10. No screw jacks.
11. Steering quickener permitted.
 
Brakes
1. No altering of stock brakes allowed. Steel brake calipers only.
2. Cars must have functioning brake on each wheel.
3. Rear disc brakes allowed. Brake assemblies must be in stock location on all 4 wheels.
4. Brake pedal must remain in stock location.
5. No brake bias or proportional valve permitted.
6. One OEM master cylinder allowed for make and model of car.
7. Steel hubs only
8. Stock style steel rotors only. No aftermarket rotors allowed. No scalloped rotors. No drilled rotors.
 
Fuel Cell Installation
1. Fuel cell mandatory. 22 gallon maximum capacity. OEM gas tank must be removed.
2. Bracing in trunk permitted
3. Trunk floor plan may be cut out to accommodate fuel cell.
4. Fuel cell must be mounted in trunk area between frame rails with at least 1 ½” clearance on all four sides. Minimum of two, 12 gauge 1 ½ inch wide safety straps mandatory.
5. No electrical fuel pumps.
6. Fuel line from trunk to engine compartment must be steel or steel braided. No copper or rubber tubing allowed. Any fuel line that runs through driver’s compartment must be enclosed in rigid tubing from inside trunk area to inside engine compartment and must be sealed on both ends. Fuel line system must be approved by race official.
7. Fuel cell will be minimum of 12” above the ground or above center line of rear differential housing, whichever is highest.
 
Engine
1. Engine block will be stock OEM small block passenger car for make and model of car.
2. No 400 blocks.
3. 350ci Chevy, 350ci Ford, and 360ci Chrysler allowed.
4. Blocks numbers must be legible upon inspection.
5. Engine must remain stock (see below specifics)
6. All engines must be stock stroke. 5.7in rods mandatory on Chevy engines.
7. Engine studs allowed.
8. No solid mechanical or roller cams allowed.
9. Engine will be mounted in stock OEM position. No alterations of front sub or cross member.
10. Stock rubber motor mounts. 1 chain will be allowed. In lieu of rubber mounts, solid steel nonadjustable engine mounts may be used.
11. No engine swapping between make and model of car (no Chevy engines in Ford cars etc.)
12. No external vacuum canisters.
13. Must idle at minimum 800rpms.
14. Maximum cylinder compression is 180lbs. Dome pistons not allowed. Flat top 2-valve relief pistons allowed.
 
 
Cylinder Heads
1. Steel stock heads only.
2. No aftermarket or bowtie heads allowed.
3. No vortec, double hump, or any type of factory performance heads allowed.
4. No Ford SVO heads
5. No aluminum heads allowed.
6. No port work allowed.
7. No roller rockers or roller-tipped rockers. Must be stamped steel rocker arms 1.5 ratio max (no 1.6 or higher ratios allowed).
8. No stud girdles
9. Aluminum valve covers with raised crank case breathers/filters permitted.
 
 
Intake Manifold and Carburetor
1. One Holley 2 bbl 4412 500cfm with stock 1.378 max venturi bore ONLY.
2. Manifold must be cast iron and unaltered.
3. Intake Manifold must be strictly stock for make and model of car. No alterations, porting, or polishing.
4. No high-rise truck or marine type intake manifolds.
5. Carburetor may be pulled for intake inspection per race official’s discretion.
6. A direct port in intake to check vacuum is mandatory.
7. No fuel injection allowed.
8. Aftermarket air filter housing and filter allowed.
   
 
Exhaust
1. Cast iron exhaust manifolds only.
2. No center dump exhaust systems.
3. No marine/boat manifolds.
4. Exhaust must run underneath car and past driver’s seat as to dispel exhaust fumes away from driver.
 
 
Fuel System
1. No electric fuel pumps allowed.
2. Stock manual fuel pump mounted in stock location on engine.
3. Fuel shut-off valve highly recommended.
4. No E85 fuel allowed. Maximum gas octane of 93 is permitted.
 
 
Electrical / Battery
1. No dual point distributors.
2. Stock coil in stock location. Stock HEI distributor only.
3. Battery must be securely mounted inside plastic battery safety box.
4. Battery box will be securely mounted to frame or roll cage bars behind driver’s seat.
5. Plastic safety box will be securely mounted to battery box.
6. Battery lines running from battery through front firewall must be mounted in flexible tubing (i.e. garden hose etc.) and sealed at both ends.
7. Ground wire will be directly attached to frame or roll bar.
8. A battery disconnect switch/kill switch with clearly marked on/off label is required within reach for safety officials.
9. Stock starter only. No mini-starters allowed.
 
 
Cooling System
1. Stock radiator in stock location.
2. Aluminum or plastic radiator allowed in stock location.
3. No electric fans.
4. Aluminum water pump allowed.
 
 
Transmission
1. Stock OEM manual or automatic allowed.
2. OEM stock turbo 350 or 400 automatic with 3 forward gears and 1 reverse gear allowed. Stock torque converter only.
3. Stock OEM manual transmissions allowed with stock single disc clutch inside an explosion-proof steel bellhousing. No aluminum transmissions.
4. Aftermarket clutch pedal assembly permitted.
5. No aftermarket made-for-racing transmissions allowed (i.e. Bert, Brinn, Falcon)
6. No powerglides.
7. Transmission must function at engine idle.
8. Stock rear transmission mounts only. Stock transmission mount cross member bolted or welded to frame.
 
 
Rear end differential
1. Steel Ford 9" floater rearends allowed. Stock steel mounts must be in stock location for year and make of car.
2. Posi-traction limited slip, locked or welded, spider gears allowed.
 
Wheels
1. Reinforced racing type steel wheels mandatory.
2. Right rear bead lock only.
3. 1” lug nuts mandatory on all wheels.
4. Maximum wheel width is 8”.
 
Tires
1. Tires must be 70 Series DOT approved.
2. 15” DOT street tire allowed.
3. Maximum tire to be 255-70-15
4. Grooving, siping, and/or soaking is not permitted.
5. Absolutely no racing tires disguised as DOT street tires.
 
Safety specific to Thundercars
1. All cars must have a window net on driver’s side. Window net must have quick release at the top.
2. All drivers must wear a neck collar.
 
Plymouth Speedway reserves the right to change, delete or add to rules throughout the racing season.
The management reserves the right of interpretation of all rules and the right to inspect and reject
any car and/or driver, crew member, etc. during the racing program.
 
For any questions on the Plymouth Speedway rules, please call Tech Director Mike Zielinski 1-(574) 532-7969
 

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