Rules Book – Addendum

PCA Club Racing has an annual process for considering changes to the rules. The period for the submission of proposed rules changes for 2019 is February 1 – June 1, 2018. Comments, suggestions, and proposals should be sent to the PCA Club Racing Rules Committee at or by using the form on this page.

Changes in safety related rules, rules clarifications, changes necessitated by external forces (e.g., specific tire availability), and editorial improvements are at the discretion of the PCA Club Racing Committee (Rules Committee) and may or may not be part of this procedure. Additionally, such changes may be published at any time as the Rules Committee may see fit. 

Changes and updates to the current Rules Book are collected here.  Drivers and mechanics are encouraged to check back on occasion to see if any  modifications have been added.  

You can use the floating “dot navigation” on the right side of the page to jump around to individual sections.  Clicking the top dot, for example, returns you to the top of the page.  Similarily, clicking the the bottom button will jump to the page footer.

    Page Index

    Specific rules changes can be found in the following index.  Clink on a link or use your browser’s search function (Ctrl-f) to look for specific keywords.

    01/25/18 – SP911 Class Rules Update
    01/25/18 – SP911 Rule 1, Chassis, Body and Interior
    01/25/18 – SP911 Rule 2, Engine
    01/25/18 – SP911 Rule 3, Transmission and Clutch
    01/25/18 – SP911 Rule 4, Suspension
    01/25/18 – SP911 Rule 5, Tires, Wheels and Brakes
    01/25/18 – SP911 Rule 6, Weight
    01/27/18 – SP997 Rule 1.G, Engine
    01/27/18 – SP997 Rule 2.E, Suspension
    02/25/18 – Splitters in Stock Classes
    02/25/18 – Serpentine Fan Belts
    02/25/18 – GTC3 ABS Replacement
    03/23/18 – SP911 Roll Cages
    03/23/18 – SPC ABS
    03/23/18 – SPC Tire and Contingency
    03/23/18 – GTD Weight
    03/23/18 – GTC7 ABS Disable

    SP997 Engine Update

    Engine Rule 1.G is changed to read:

    Computer Engine Management System. The ECU and the flash of the computer engine management system must remain stock, with two exceptions: It may be dealer re-flashed and the appropriate switch and factory Sport Plus software program may be installed to include sport plus mode in cars without the Sport Chrono (sport plus) option (software must be 2009‐2012 997.2 factory settings). And the Topp Racing SP997 ECU Flash v1.0 is allowed. No aftermarket chips are allowed.

    SP997 Suspension Update

    The spring rates in Suspension Rule 2.E are changed to read:

    Front spring 500‐600, rear spring 600‐700.

    SP911 Class Rules

    Existing class rules are replaced with the following text:

    This class is for 911s with air-cooled 3.0L and 3.2L engines. Note for 2018 – SP911s which were raced with PCA in 2017 with a 2.7 liter engine may race in this class in 2018 under the engine rules and weight contained in the 2017 rules, but that engine is phased out of the class entirely as of 2019. Modifications not specifically listed below are prohibited. Where “stock” is specified, it means the components must remain stock. No material can be added or removed; no re-allocation of weight or material can be performed. No material can be substituted for another material of similar geometry. PCA will honor approvals of modifications of items not in compliance with the rules if the approval has been noted in a vehicle logbook. PCA Club Racing will honor prior written approvals of modifications not listed here by the sanctioning body from which these rules originated.

    1. Chassis, Body and Interior
      1. Any Porsche 911 chassis up to 1989 is allowed except for turbo or turbo-look body shell.
      2. Bolt-on fiberglass and composite replacements of front and rear bumpers, rear deck lids/tails, front fenders, and front hood are allowed. Bonded or glued fiberglass or composite sunroof “plugs” and fender flares are allowed. Fiberglass or composite rear fender flares may include most of the rear fender as long as steel remains around the perimeter of the fender. Substitution of other parts is not allowed. Fender flare configuration is free.
      3. Cars must have a windshield, a rear window and rear quarter windows. Cabriolet bodies must have a stock size windscreen and no other windows are required. Materials may be original equipment or equivalent glass, polycarbonate, or other break-resistant plastic.
      4. Rear wing choices include: ducktail, 911 whale tail, 930, IROC, large IROC, 911 3.6 RS wing, 3.8 RSR short wing. Wicker bills up to 1″ can be added to the ducktail, 911 whale tail, 930, IROC and large IROC tails.
      5. Any front air dam may be used as long as it does not extend forward of the stock front bumper (excluding bumperettes).
      6. Interior modifications are free.
      7. Electrical system and instrumentation is free.
      8. External lights, including brake lights, are free, but at least two brake lights must be in the stock fender locations and at least as visible as stock lights.
    1. Engine
      1. All engines must run on standard pump gas with octane rating not to exceed 93.
      2. Exhaust system may have any header system with a maximum primary tube size of 1.5″ outside diameter. The 3.2 liter motors may increase the primary tube size up to 1.625″ OD.
      3. Crankcase can be any 911 crankcase and machining of any kind is allowed.
      4. Rods must be stock. Aftermarket rods bolts are allowed.
      5. Valve springs & retainers are free, but all engines must have a functioning rev limiter set at no higher than 7,200 rpm.
      6. Ignition system is free as long as it is single plug per cylinder.
      7. Engine oil system and cooling is free.
      8. Fuel must be street car pump fuel and no higher octane than pump premium readily available from gas stations in the state in which the race is head, or adjacent states if they are at a distance reasonable for hotel accommodations for the event. No race fuels, additives or mixing allowed.
      9. 3.0 liter engine specs
        • Allowable intake systems are: 40 or 46 mm Weber or PMO carbs, CIS intake manifold from any year and with any fuel injection system, Bosch low butterfly MFI from 1969-1973, 3.2 intake manifold with any throttle body and airflow meter, “straight-through” fuel injection systems with individual throttle bodies no larger than 46 mm (e.g., TWM, Jenvey, etc.), 3.6 intake manifold from 1989-1995 911 with any throttle body(s). Slide valve intakes are prohibited.
        • Crankshaft: stock 70.4 mm stroke with 9 bolt flywheel configuration.
        • Pistons and cylinders: any stock CIS 911 SC 95 mm bore. Replica pistons from Rothsport Racing are allowed. Maximum compression ratio is 9.8:1.
        • Cylinder Heads: maximum port sized of 39 mm intake, 35 mm exhaust and valve sizes of 49 mm intake and 41.5 mm exhaust. Small intake port 3.0 liter heads may have cylinder head material removed to match the port shape and dimensions of the large, stock 3.0 intake port.
        • Camshafts: stock 911SC.
    1. Transmission and Clutch
      1. Models up through 1986 must have a Porsche 915. 1987-89 cars may use a Porsche G-50 transmission. The transmission must use Porsche synchronizers.
      2. Differential is free.
      3. Clutch package is free. An unmodified stock flywheel must be used on all transmissions.
      4. Transmission coolers, lubrication, and shift linkage are free.
      5. 915 transmissions must use an 8:31 final drive ratio. G-50 transmissions must use the 9:31 final drive ratio.
      6. The following gear rations are acceptable in any combination:
      915 Transmission G-50 Transmission
    1st Gear 11:35 12:42
    2nd Gear 18:33 or 18:32 17:35
    3rd Gear 23:29 22:21
    4th Gear 26:25 or 26:26 32:36
    5th Gear 28:23 36:32
    1. Suspension
      1. Stock suspension pivot axis must be maintained by all suspension components.
      2. Front spindle height is free; struts must be O.E. components manufactured by Boge, Bilstein or Koni with the location of the spindle as standard or relocated. The retaining system for the O.E. shock absorber insert must be used. Custom fabricated strut housings are not permitted.
      3. Front and rear shock absorbers must be the same configuration as stock, maximum 2-way adjustment.
      4. Torsion bar suspension required, front and rear. Torsion bar length and receiver locations must be stock.
      5. Suspension bushings are free. Front camber plate/caster plate design is free.
      6. Stock 911 rear control arms only, 930 rear control arms are not allowed.
      7. Adjustable rear spring plates are free.
      8. Anti-roll bar (sway bar) systems are free.
      9. Alignment settings are free, except track width can only be increased from stock by .25 inches per side. Track width must not exceed 65 inces in front and 67 inches in the rear. Measurement is from furthest outside lip of tire on axle center line.
      10. The rear minimum ride height is 215 mm from ground to center of rear torsion bar, with driver in car and the spec tire at 35 PSI.
    1. Tires, Wheels and Brakes
      1. Wheels must be 7×16 front and 8×16 rear. Any aftermarket wheel is allowed.
      2. Tires must be Hoosier R7’s 205 or 225 x 16 fronts and 245 x 16 rears. Hoosier rain tires allowed to correspond o R7’s sizing. Toyo RR or R888 225/50-16 front and 245/45-16 rear may also be used.
      3. Any brake caliper, pad and rotor combination is allowed as long as they fit inside the require wheel size and the roters are steel
      4. Brake lines, air ducting, master cylinder, brake balance control and fluid are free. Dust shields may be removed.
      5. E-brake, parking brake or hand brake system may be removed.
    1. Weight. The minimum weight for this class is 2350 pounds. However, if the car displays a Porsche Racing Club sticker indicating a higher minimum weight, that shall be the weight which must be met.

    SP911 Roll Cages

    Roll cages may extend through firewalls and tubing may connect shock towers and extend to the front of the trunk.  Shock mounts may be altered to accept camber plates.  Tub sheet metal interior to the body skin in the trunk forward of the firewall  may be cut out, altered, and ducted for oil or brake cooling air flow.  Openings in the front air dam (below the bumper) for oil and brake cooling are free.

    These changes clarify longstanding SP911 practices which were not explicit in the published rules.  They cover running roll cage extensions through the front and rear firewalls, welded (or other) shock tower braces, camber boxes, locating front oil coolers in the front of the trunk, or ducting coolers into the trunk.  Making openings in the trunk lid, bumper (above the spoiler), or fenders for air inlets or outlets or otherwise is still not allowed. 

    Racers who identify other common SP911 practices concerning the car which can’t be tied to a published rule which would allow it are encouraged to submit rules change proposals so those can be clarified

    Splitters in Stock Classes

    “Splitter” is not a term currently used in the rules. It is justified by reference in the rules to bumpers, spoilers (aka the valance under the bumper), and air dams (same). Some of the aftermarket pieces allowed under these rules incorporate a lip at their base, which acts as a splitter. Some do not, and racers add a splitter element. The rules limit the projection of these parts to zero for stock body width and one inch for stock body length. They are silent on rearward (under tray) extension. There is justification for allowing rearward extension to tie in with the tub at the front of the trunk to strengthen the often-fragile lower front of any aftermarket air dam, and at the sides to allow directing more air to the brake rotors (a feature later Porsches with extensive stock plastic undertray parts incorporate). Effective immediately, the following rule governs and limits this rearward extension.

    In Stock and Prepared, 911s through 1989 may extend a permitted air dam rearward under the car to the front of the stock gas tank chassis opening, extended sideways at right angles to the car centerline. Channels or ducts may be incorporated into the portion of this extension outboard of the tub for the purpose of channeling front brake cooling air.

    Suggestions for how such an allowance should be applied to other models should be submitted to A reminder: if there is a question, send an email and receive a clarification before doing any modifications .

    Serpentine Fan Belts

    No rule affecting Stock or Prepared cars permits replacing a V-belt drive on the engine with a serpentine (flat multi-groove belt with a tensioner/idler).

    Stock class air cooled 911s which have had their V belt fan and alternator belt or belts converted to a serpentine system that has ratios that lower the fan and or alternator speed will add 25 pounds to their minimum weight.

    It appears that no serpentine kit currently available for the 3.0 or 3.2s has stock ratios. It also appears that all available kits slightly lower the fan and alternator speeds. V belt drives must use stock ratios in Stock.

    Stock Engine 1.P. and Prepared Engine 1.I rules provide that under driving fans, alternators, and pumps of any sort from stock pulley ratios is a Prepared modification (except for under driving the power steering pump on the Boxster/Cayman, which is permitted in Stock). This means that an air cooled 911 running as a Prepared Stock class car may under drive the fan/alternator (single drive) or either the fan or the alternator or both (dual drive or dual to single drive conversion) as a Prepared change. As the serpentine itself does not affect power, such a system may be used as a Prepared change.

    The PCA Club Racing National Staff is studying this issue. A rule change proposal will be included in the rules proposal cycle this year. 

    Racers are reminded that the avenue for approval of modifications is submitting a rules change proposal. The Club Race Technical and Rules chair has the authority to make interpretations of existing rules as applied to specific car parts, and to approve substitutions when Porsche parts become no longer available. While the goal of rules writing is to be clear and unambiguous, racers uncertain about the application of a rule are encouraged to ask the Rules Chair for an interpretation. Where interpretation is involved (the rule book itself answers many questions with no need for interpretation), it is always given in writing (nowadays via e-mail) with a notation that the e-mail be printed and placed in the log book. But interpretation does not include approving modifications not tied to existing rules. The main existing rule says that if you can’t point to a specific rule allowing X, you can’t do X. Rules normally get changed through the annual rules change process, which includes provision for racer comment. Where circumstances warrant faster action, the Rules Committee discusses the matter before acting with the approval of the Club Race Chair and publishing the change, which is what happened with the splitters discussed above. Racers who believe that allowing replacing V belts with serpentines is beneficial to Club Racing should consider submitting a rules change proposal.

    GTC3 ABS Replacement

    The main ABS unit for the 996 Cup cars is no longer available from Porsche and finding a used one in good condition is difficult if not impossible. For one reason or another, these units can become inoperative. Effective immediately, racers in GTC3 may replace the factory ABS with the DeMan Motorsport 996 Cup ABS Replacement Kit, which is based on parts used by Porsche. A copy of the sale invoice should be placed in the car’s logbook.


    SPC cars may have the Bosch ABS PCCB program in the ABS module selected.  The module contains a regular and a PCCB program, and a PWIS tool can select either, so any dealer can do this.  The PCCB programing should be more resistant to “ice mode.”  If the experience from Watkins Glen or later shows unanticipated problems, this allowance may be discontinued.  Note this applies only to the programming, and does not allow PCCB rotors or calipers or other components.

    SPC Tire and Contingency

    The 2018 spec tire for SPC is the Hoosier R7 – 245/35-18 front, 295/30-18 rear.  H2O Rain Tire: Front: 225/40-R18  Rear: 275/35-R18.

    Because the Hoosier 295/30-18 tires for the rear are wider than the previous spec tire, and spacers are needed to avoid rubbing on the strut, rule 3.D. prohibiting tires from extending beyond the fender does not apply in the rear as long as the spacers used are no wider than necessary to prevent rubbing. 

    In addition, SPC rule 6.A.(12 is amended to delete the requirement and specifics for Toyo stickers.  Racers wishing to participate in the Hoosier contingency program must register with Hoosier and display the decals in the sizes and locations specified, and sew a Hoosier patch on their driver’s suit.  Program details are available on the Club Racing website under Sponsor Contingency.

    GTD Weight

    Minimum weight for all models in this class is 3100 lbs.

    GTC7 ABS Disable

    991.2 Cup Cars (PCA GTC7 eligible) may install the IMSA Platinum Masters required Part# PMNMTH355200 991.2 Cup Bosch ABS Kit, Porsche Motorsports ABS System.  If this ABS has been disabled by a method approved by the Club Race Rules Committee, and  the car is presented at tech to have compliance noted and seals applied if needed and runs without ABS during the event, it may run in GTC7.  Otherwise, 991.2 Cup Cars must run in GTA3 if they have installed an ABS.  Drivers wishing to disable the ABS should correspond with Club Racing Rules Committee well in advance of an event to discuss the method to be used and gain approval. This is a revision deleting the requirement of a specific method from that previously announced.  And note:  of the other GTC classes, only the GTC3 996 Cups may have an ABS installed.