Interim Rule Changes for 2025

QUICK LINKS

Use the links below to jump directly to specific changes:

• SPEC Tires
• GTB

SPEC Tires

SP911

Hoosier no longer makes the 245/45-16 spec rear rain tire. In addition to using the spec rear which racers may have, they may use the spec (for the front rim) Hoosier rain 225/50-16 on the rear rim as well. SP911racers should discuss what further options for rain tires might be beneficial to the class (for instance, also allowing Toyo RA1s as rains, or allowing any DOT stamped tires as rains) in the future and consider submitting a consensus proposal for the 2026 rules by June 1, 2025. Who knows how long a particular tire model will continue to be manufactured.

ME1

In addition to the Toyo R and left over RRs, all of which may be used for 2025, the following Hankook tires may be used and will be the spec dry tire for the class going forward:

Z214 C51 medium compound tire, 225/45ZR17 for 7″ rims and 245/40ZR17 for 8.5″ rims.

In addition, the Hankook Z207 W52 medium compound rain tires may be used:

200/620R17 for the 7″ rim and 235/620R17 for the 8.5″ rim.

GTB engine air intake modification rule change

Engine heat has always been a particularly acute problem with the Caymans on the race track. Following Porsche’s lead with its factory race Clubsports, PCA recently allowed the GTB 981s to draw intake air from alternate locations less susceptible to heat above ambient without compromise to firewall integrity, either using the Porsche approved parts or similar aftermarket parts. The configuration of the 987 intake does not allow quite the same modification, but parity requires affording that model a substantially similar modification. Accordingly, the GTB1 rules for Cayman engines listed below are modified to read as follows.

1. 1. Engine:

1. 1. 3. For the purposes of the requirement of an unmodified stock engine, the engine begins at the input to the stock MAF sensor (911) or throttle body (987 or 981) and ends where the exhaust manifold is attached.

1. 1. 11. The following Cayman intake air modifications prior to the throttle body may be made. The vertical rear engine compartment firewall into the trunk space may be penetrated via a sealed hole. If not using the Manthey Racing intake, any bulkhead pass-thru connector going through the firewall must be metal. The air box and air filter components (other than the filter element) located in the trunk space must be metal, carbon fiber or high grade, high temperature plastic. Any suitable water cooled six cylinder Porsche OEM air box is also acceptable for the filter.

1. 1. 1. 1. 987 Caymans must use the stock factory MAF sensor but it may be moved from the original location, including into the trunk area. MAF sensor wiring can be lengthened and routed accordingly. The rubber bellows hose (air guide) may be replaced to connect the stock throttle body (throttle valve adapter) to the bulkhead pass through.
         2. 981 Caymans may run the Porsche 718 style Cayman GT4 Clubsport Manthey Racing SRO intake air modification that exists before the air reaches the throttle body. Similar aftermarket systems may also be used
         3. Such systems may receive the air either from the quarter windows or from ducts or scoops in the rear window or rear hatch, and electronic and other parts within the rear trunk may be relocated within that space as needed. It is recommended that flexible ducting from air filters to reach ambient air inlets should of at least brake duct heat resistance quality.