These specifications are part of the SCCA GCR and all automobiles shall conform to GCR Section 9.
A. PURPOSE AND INTENT
The Spec Miata (SM) class is intended to provide the membership with the opportunity to compete in low cost, production-based cars with limited modifications, suitable for racing competition.
The rules are intentionally designed to be more open than the Showroom Stock class but more restricted than the Improved Touring class.
The vehicle identification number (VIN) shall correspond with the model-year automobile classified. VIN plates or stampings shall remain in place. There must be a minimum of two (2) VIN plates or stampings that correspond with the model year automobile classified.
B. CLASSIFIED CARS AND WEIGHTS
Classified cars and weights are listed on the Spec Miata Specification Table.
Cars are to be weighed with the driver and required ballast. See GCR Section 9.3.8.
C. AUTHORIZED MODIFICATIONS
The following items represent the only modifications and safety items permitted and/or required on Spec Miata automobiles other than safety items as required in Section 9. No permitted component/modification shall additionally perform a prohibited function. No updating or backdating of cars, models, specifications, and/or components thereof shall be permitted except as specifically authorized in these specifications.
A Shop Manual for the specific make, model, and year of automobile is required to be in the possession of each entrant. The manual is intended to aid Scrutineers in identifying parts and the configuration of the automobile. Overhaul procedures that in the slightest way would increase performance are not to be utilized; e.g., porting, etc. Blueprinting and balancing are inconsistent with the philosophy of this class and are not permitted.
All adjustments shall be at the manufacturer’s specification and/or within the manufacturer’s specified tolerances except as permitted within the SMCS.
Stock replacement parts may be obtained from sources other than the manufacturer provided they are the exact equivalent of the original parts. The intent of this rule is to allow the competitor to obtain replacement parts from standard industry outlets, e.g., auto-parts distributors, rather than from the manufacturer. It is not intended to allow parts that do not meet all dimensional and material specifications of new parts from the manufacturer.
The application and/or use of any painting, coating, plating, or impregnating substance (i.e. anti-friction, thermal barrier, oil shedding coatings, chrome, anodizing, etc.) to any internal engine surface, transmission, differential, internal or external surfaces of the exhaust manifold or down-tube, is prohibited.
1. Engine Modifications
a. Induction System
1.All air entering the intake tract shall pass through the fuel injection air inlet.
2.1.6L cars may replace the stock air box with a cone style air filter assembly. The air filter element is unrestricted. No ducting or baffling of air to the air filter is permitted.
3.1.6L cars may open and adjust, but not modify, the OEM airflow meter. For 1.6L cars, the position of the air flow meter may be moved provided it remains attached to the unmodified factory intake tube.
4.1.8L cars must use the stock air box, but the air filter element is unrestricted.
5.1.8L cars shall use an air restrictor. The throttle restrictor shall be placed between the throttle body and plenum. All intake air shall pass through the restrictor plate. Restrictor plates must be the proper size as listed in the Specification Table, must be from Mazdaspeed Motorsports Development, and must not be modified.
b. Fluid hoses and clamps, oil filters, fuel filters, and belts (fan, alternator, etc.) may be substituted with others of equivalent OEM specifications.
c. Fuel System
1.Unleaded fuel filler trap door and restrictor plate in filler neck may be removed.
2.Refer to GCR Section 9.3.25 for permitted fuel specifications and for the required fuel sample acquisition port.
d. Ignition/Electrical System
1.Spark plugs and spark plug wires may be substituted.
2.Ignition timing is unrestricted within stock adjustment capability.
3.Batteries may be replaced with those of an alternate manufacturer, provided they are of similar amp-hour capacity, size, and weight and are fitted in the standard location. Additional battery hold-down devices may be used, and are strongly recommended.
e. Exhaust System
The factory exhaust system beyond the OEM front down pipe may be replaced, provided:
a. Said replacement system retains the original configuration, e.g. single tube design, and the tubing diameter is a maximum of 2.25” outside diameter.
b. The pipe may end anywhere after the rear subframe. Forward of the rear subframe, the pipe must follow the original path of the OEM exhaust system.
c. No expansion chambers. A single muffler may be added.
d. The system meets all event specific sound requirements.
e. A cat replacement tube may be installed. The tube shall not exceed 17.5” in length and have an outside diameter no greater than 2.375”.
1.Original exhaust system heat shields may be removed.
2.The post catalytic converter oxygen sensor may be
disabled, replaced, or removed; the resulting hole (if present) may be plugged. 1999-05 Miatas with California emissions equipment may substitute the OEM CA exhaust manifold and catalytic converter with the Federal OEM exhaust manifold.
f. Clutch System and Flywheel: All cars shall use either the stock OEM pressure plate appropriate model year or the ACT pressure plate (Mazdaspeed p/n: 0000-0205401-SS (1.6L cars) or 0000-0205404-AC (1.8L cars)). The unmodified pressure plate shall be bolted directly to the appropriate stock, unmodified flywheel. The 94 model year may utilize the flywheel from the 95-05 model years. If the 1994 flywheel is used it shall weigh a minimum of 18.5 lbs. Any clutch disk may be used. The minimum weight (including the pilot bearing) is 17.6 lbs for the 1.6L and 17.1 lbs for the 1.8L.
g. Lubricants may be substituted with any lubricant. Oil additives are unrestricted.
h. The engine block and/or cylinder head may be decked/milled to achieve the factory specified compression ratio for the correct model year as listed on the specification table.
i. Camshafts shall comply with the Official Camshaft Data as supplied by the SCCA Club Racing Tech Department.
j. Cast iron cylinder liners (sleeves) may be installed to restore damaged or worn cylinder bores to the original dimension.
2. Cooling System
a. Any radiator may be used, provided it is mounted in the original location, maintains the same plane as the original core and requires no body or structure modifications to install. Any openings created by fittng an alternate radiator shall be blocked to prevent air from entering the engine compartment. The stock cooling fan(s) must be maintained. At least one functional stock OEM cooling fan must be mounted in one of the stock locations.
b. Thermostats may be modified, removed, or replaced.
c. All cars may install the Upper Radiator Seal, p/n NA75-50-OK7A
d. A radiator screen of one-fourth (1/4) inch minimum mesh may be added in front of the radiator and contained within the bodywork.
e. The factory air conditioning systems may be removed. Items that serve a dual purpose, such as the alternator/air conditioning compressor bracket, may not be substituted.
f. Engine coolant fluid, coolant/heater hoses and clamps may be substituted. Heater core may be bypassed. It may not be modified or removed. Heater water control valve(s) may be added or substituted.
3. Transmission/Final Drive
a. Transmission and final drive ratios must remain stock for the year of car. 1999-up cars shall only use the 5 speed transmission and the 4.3 differential ratio. All cars may use the stock unmodified OEM open differential or one of the approved alternates listed below.
b. 1990 to 1993 Miatas may use the stock, unmodified viscous limited slip differential or the MAZDASPEED Motorsports Development limited slip differential, part number #QN10-64-A00 (previously TOY1-27-200 & 0000-02- 5501).
c. 1994 and newer cars may use the stock Torsen limited slip differential.
d. The 90-93 Miatas may convert to the 99-05 differential housing and the 4.3 differential gear ratio from the 99-05 model years. This conversion includes the driveshaft and half-shafts. The original 90-93 model rear suspension uprights must be retained.
e. Lubricants may be substituted with any lubricant.
Suspension modifications are limited to the addition of the MAZDASPEED Motorsports Development “Spec Miata kit” and those modifications detailed in this area.
a. MAZDASPEED Motorsports Development Spec Miata kit 1990-93 1.6 DOHC K-SPEC-M5-SUSP 1994-97 1.8 DOHC K-SPEC-M5-SUS8 1999-up 1.8 DOHC K-SPEC-M5-SUS9
The following is a breakdown of components supplied within these kits. All parts numbers are MAZDASPEED Motorsports Development parts numbers. No substitution of parts is allowed. The kits must be used in their entirety.
1.Shocks Front Bilstein 0000-04-5225-BL Rear Bilstein 0000-04-5226-BL
2.Springs Front Eibach ERS 700 lbs/6” 0000-04-9700-06 Rear Eibach ERS 325 lbs/7” 0000-04-9325-07
3.Coil-Over kit Front/Rear 0000-04-5402AW
4.Anti-Roll Bars K-SPEC-M5-SUSP Eibach kit - front / rear bars 0000-04-5302-EB Front 24mm Adjustable Rear 15mm Adjustable K-SPEC-M5-SUS8 Eibach kit - front / rear bars 0000-04-5303-EB Front 27mm non-Adjustable Rear 15mm Adjustable K-SPEC-M5-SUSP9 Eibach kit – front / rear bars 000-04-5304-EB Front 27mm non-Adjustable Rear 15mm Adjustable
b. All cars shall use unmodified Mazdaspeed bump stop (Part # 0000-04-5993AW).
1999-up cars shall use the bump stops from the Mazdaspeed kit (p/n 0000-04-5993-AW) in conjunction with the 1999-up stock upper mount assembly consisting of the upper mount (p/n: NC10-28-340C), the upper mount bushing (p/n: NC10-28-776) and the upper mount washer (p/n: NC10-28-774), and shock body spacer over the shock shaft (p/n 1234-56-789-AW). All other OEM upper mounting hardware shall be discarded. 1990-1997 cars may use the bump stops from the Mazdaspeed kit (p/n 0000-04-5993-AW) in conjunction with the 1999-up stock upper mount assembly consisting of the upper mount (p/n: NC10-28-340C), the lower mount bushing (p/n: NC10-28-776) and the upper mount washer (p/n: NC10-28-774). Non-OEM equivalents may be used in place of the upper mount, upper mount bushing, and upper mount washer only. No other modifications are allowed.
A metal or delrin plastic spacer as shown below may be added between the Mazda bump stop and the 1999 shock hat. The 0.31” measurement is +/- 0.01 in. All other measurements are non-critical and are shown for clarification purposes only. In addition, a 3/8” steel hardware washer may be installed between the shock shaft and the bump stop. The washer shall be a maximum of 1/8” thick.
c. Subframe braces may be updated to stock 1997 configuration utilizing the MAZDASPEED Motorsports Development Spec Miata kit.
d. Anti-roll bar links may be replaced and may be adjustable, but the attachment points must remain stock. The control arms and specified anti-roll bar may not be modified. One end of the sway bar(s) may be disconnected as a suspension tuning aid. The bar must remain in place and be solidly attached to the suspension on one end.
e. Suspension alignments (camber, caster, toe) are unrestricted within the limits of the unmodified factory adjustments. Minimum ride height is unrestricted.
f. No relocation or reinforcement of any suspension component or mounting points is permitted.
g. Hardware items (nuts & bolts) may be replaced by similar items performing the same fastening function(s).
h. Manual or power steering racks may be used. Power steering racks may be converted to manual by removing all power steering components.
i. Towing eyes per GCR Section 9.3.46 are required. Stock towing eyes may be modified, replaced, or removed but may serve no other purpose.
j. Hubcaps and wheel trim shall be removed.
k. All chassis/structural/electrical repairs, if performed, shall be in concurrence with factory procedures, specifications, and dimensions. Unless specifically authorized by the manufacturer for repair or allowed by these rules, no reinforcement, i.e., seam welding, material addition, etc., is permitted.
l. The front shock tower connector/brace is not permitted on the 1999 and newer cars.
a. Backing plates and dirt shields may be ventilated or removed.
b. Brake lines may be replaced with steel lines or Teflon lined metal braided hose.
c. Cars with antilock braking systems must have the system disabled as specified in GCR 9.3.11.
d. Parking brake mechanisms, and actuating components may be removed.
e. Brake pads and brake fluid are unrestricted
f. 2001 and newer cars must use the 255mm(F) and 252mm(R) brakes. The larger brakes 269.5mm(F) and 267.9mm(R) are not permitted.
Any wheel/tire may be used within the following limitations:
a. Required rim diameter is fifteen (15) inches. Maximum rim width is seven (7) inches. Minimum weight of wheel shall be 13 lbs without spacers.
b. Other than the stock 15” Mazda steel wheel, all wheels must be one-piece metal castings (not multi-piece wheels, bolted, riveted or welded together).
1.1. National Competition All cars shall use the Toyo R888 (205/50R15)
2.2. Regional Competition Any DOT approved tire is permitted. Racing, recapped, or regrooved tires are not allowed. Tire size is unrestricted. The only modifications allowed to tires are having treads “shaved” or “trued.” Individual regions may require spec tires for regional races. Supplemental regulations for specific events should be checked.
d. The front track shall not exceed 1450 mm. The rear track shall not exceed 1465 mm for the 90-97 model years and 1475 mm for the 99-05. Aftermarket wheel studs, lug nuts, and wheel spacers are permitted. If spacers are used they shall be no greater than 13 mm and equal on all four corners (i.e. no offset stagger side to side). e. Tire tread (that portion of the tire that contacts the ground under static conditions) shall not protrude beyond the fender opening when viewed from the top perpendicular to the ground. To determine compliance, the vehicle should be rolled through a powdered substance, as raced with driver, in order to indicate the tire tread contact patch under static conditions.
a. Fenders and wheel openings shall remain unmodified. It is permitted to roll under or flatten any interior lip on the wheel opening for tire clearance. Non metallic inner fender liners may be removed.
b. Body repair shall be performed using every reasonable effort to maintain stock body contours, lips, etc. Any body repair modification having as its purpose increased clearance is prohibited.
c. The “R” package Miata chin spoiler is allowed on 1990-1997 cars provided it is mounted in the OEM location. 1999-up cars may use the OEM chin spoiler for these cars (99-00 p/n: NC10-V4-900F or 01-05 p/n: NO67-V4-900G). Rear spoilers including OEM design are prohibited.
d. Windshield Clips/Rear Window Straps per GCR Section 9.3.53. are permitted and recommended.
e. Convertible tops and attaching hardware shall be completely removed. Cars may compete with the Mazda factory detachable hard top in place (latches shall be replaced with positive fasteners), but it is not mandatory. When no top is used, driver shall wear arm restraints, and the cage will meet the helmet clearance rule.
f. Body side moldings, rocker panel moldings, and wheel opening trim pieces may be removed.
g. The plastic trim on the hood may be removed.
h. Hood and trunk clips are permitted. Stock hood and trunk latches may be disabled or removed.
i. Ducting may be added to provide fresh air to the driver compartment. This ducting shall be located in the driver and/or passenger vent window area by means of a transparent/alter-nate vent window material and duct with no modifications to the bodywork. To improve driver exit through the window area, the driver vent window and vent window supporting frame may be removed as a pair. If removed, ducting may be in the passenger side vent window only.
j. Radio antennas may be removed. Antennas for two-way radios may be added.
8. Driver/Passenger Compartment - Trunk
a. The driver’s seat shall be replaced with a one-piece bucket-type race seat. All seat mountings shall be reinforced. Factory seat tracks/brackets may be modified, reinforced, and/or removed to facilitate replacement mountings provided they perform no other function. The passenger seat must be removed.
b. Any steering wheel, except wood rimmed types, and its required mounting modifications may be used. Any shift knob may be used.
c. Gauges and instruments may be added, replaced, or removed. They may be installed in the original instrument(s) location using a mounting plate(s), or any other location using a secure method of attachment. Other than modifications make to mount instruments and provide for roll cage installation, the remainder of the dash “board” or panel shall remain intact.
d. Any interior or exterior mirrors may be used.
e. Carpets, center consoles, cargo bins, seat belts, floor mat, radio system, headliners, dome lights, grab handles, sun visors and their insulating and attaching materials may be removed. Other than to provide for the installation of required safety equipment or other authorized modifications, no other driver/ passenger compartment alterations or gutting are permitted.
f. Two way radios may be used.
g. Spare wheels and tires, jacks and tools shall be removed from the cargo/trunk area. Spare tire covers and trunk mats and/or trunk carpeting shall be removed.
h. Modifications may be made to the foot pedals to improve the comfort and accessibility to the driver. Dead pedal/foot rest and heel stop may be added.
i. If ballast is required to meet the required weight it shall be added as follows:
1.All ballast shall be securely mounted on the passenger floor.
2.Each segment of ballast shall be fastened with a minimum of two (2) one-half (1/2) inch bolts and positive lock nuts of SAE Grade 5 or better and shall utilize large diameter, load distributing washers.
3.Holes may be drilled in the passenger floorpan for the purposes of mounting the ballast and the floorpan may be reinforced for that purpose only.
j. All cars shall run with both front door windows fully open (down).
a. An electrical master (“kill”) switch is required. See GCR Section 9.3.33.
b. Installation of a fire extinguisher or fire system is required. See GCR 9.3.22.
c. Air bag systems shall be disarmed and may be removed.
d. In any automobile where allowed removal of upholstery, seat belts, etc., creates an opening between the driver/passenger compartment and an exposed gas tank, or part thereof, including the filler tube, a metal bulkhead which completely fills such opening shall be installed. See GCR 9.3.26