Rule Changes for 2025

QUICK LINKS

Use these links to jump directly to specific changes:

• Stock
• Prepared
• SP1
• SPB
• SPC
• GTB1
• GTC
• GTD
• Firewall
• Proposal for Comment

Stock

1. Some Spec or other classes specifically allow minor modifications which are not expressly allowed in Stock, but which are often found on dedicated track cars when race prepared. Adding the following allowances to Stock will permit shortening some Spec class rules (at least any future ones), and clarify what is allowed in stock to reinforce the “if it isn’t allowed it is forbidden” approach in Stock. Most of these questions have arisen or at least been foreseen in one or more Spec classes:
• Emergency brake lever, cables, and associated parts may be removed.
• Clutch disk and pressure plate must be factory or aftermarket stock equivalent. This does not apply to rubber centered disks or permitted replacement of dual mass flywheels, which are governed separately.
• If hood pins are installed, stock hood latches may be removed or disabled.
• The windshield wiper arms and blades may be removed.
• Electrical wiring for parts which may be removed may be removed.
• Seam sealer, undercoating, weather stripping, and tubing for water drainage may be removed.
• Plastic fender liners may be removed, or holes cut in them.
• Thermal insulation and shielding may be removed.
• The immobilizer box may be relocated inside the driver’s compartment.
• Fuse panels may be replaced and relocated.
2. The minimum weights for F class are reduced by 100 pounds

The previous general weight reduction stopped at G. This boundary was in a sense arbitrary, based on an assessment of who was racing in which of the lower stock classes. Giving it to all cars in the class maintains the current balance of power within F.

2) Prepared

1. Cars running as Prepared may run 100 pounds lighter than their base (stock) weight.
   Prepared cars have always had to carry the weight assigned to the model in Stock, with the Prepared allowances limited to various engine, transmission, bodywork, and aero modifications. This allows prepared cars of any class to run 100 lbs lighter.
2. Aftermarket electro-hydraulic power steering pumps may be installed as a Prepared modification, if their hose end fittings will attach to an unaltered stock power rack and pinion assembly, and if this is done the power steering pump on the engine may be removed or disabled and idlers and belts may be changed accordingly.

The plastic hydraulic fluid lines from the pump on the engine to the steering servo have been a reliability issue.

3) SP1

The spec dry tire for 2025 is the Toyo R. Toyo RRs may continue to be used as long as stocks remain.

4) SPB

1. Front outer lower control arms may have longer camber adjustment studs installed.
2. The spec dry tire for 2025 is the Toyo R. Toyo RRs may continue to be used as long as stocks remain.

Slotting of the shock towers has never been allowed in SPB (nor NASA nor POC for that matter). Suspension Rule 4.A. prohibits shock tower modification. In 2024 cars found with elongated slots in the front shock towers have been required to fix this by welding steel into the shock tower slots, hence getting the strut mounts back to their maximum stock position. In 2025 cars found with unrepaired altered slots will be disqualified.

5) SPC

1. The 2007-8 2.7 liter Cayman six speed transmission is an allowed alternate transmission.

This allows a 2007-8 non-S to avoid having to change the transmission when installing the 3.4 liter S engine to run in SPC.

1. Any AOS may be used, and this may include substitute valve cover pumps and additional external plumbing as well as an aftermarket separator unit. Note this does not allow dry sump conversion or creation of a crankcase vacuum.
2. The engine may be converted to a dry sump system with an external sump tank and associated plumbing as long as the system does not create a crankcase vacuum.

6) GTB1

1. 996s and 987.1 (2006-08) Caymans in GTB1 may use the 82mm GT3 throttle body and plenum, or aftermarket versions of the same. This was the original allowance before the manufacture of the 997s and was intended to address a perceived performance imbalance. Extending it to the 997 was an editorial oversight and not necessary for performance balancing, so these intake modifications are no longer allowed for the 997.
2. GTB cars with the 981 engine may run the Porsche approved Cayman GT4 Clubsport Manthey Racing intake air modification before the air reaches the mass airflow sensor. Similar systems may also be used involving two air filters Teed into the intake via a sealed hole in the vertical rear engine compartment firewall. 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 parts within the rear trunk may be relocated there as needed.

7) GTC

1. GTC1: 1990-93 Euro Cups, and 1992 USA Cups may run any exhaust, any shock, and any suspension spring. This will allow cars so modified for other race series to race in class with PCA.
2. All: The quarter windows may have a duct added to supply air for driver cooling. If the manufacturer of such a system supplies an external scoop for a quarter window, that may be used with the system. This conforms to practice and is not a car performance advantage.

8) GTD

GTD cars will run in GT3 at 3100 pounds minimum weight if non-spec tires are the only disqualifying change. Other changes require running in the proper GT class at the calculated GT weight.

9) Firewall

CAR REQUIREMENTS APPLICABLE TO ALL CARS IN ALL CLASSES Rule 9 (Firewalls) is amended as follows:

1. Cars with the gas tank in the front trunk shielded from the trunk space by a metal firewall (SPB/996 and later style front end) may direct demisting air to the windshield via an opening in the cabin firewall under the cowl under the following conditions:

1. 1. If factory cabin air handling components are modified, any tubing added must be fire rated to 1,500 degrees F.
   2. If the right side factory cabin air inlet cannot be used for this purpose (e.g., permitted roll cage/reinforcing members intrude), a hole may be made in the firewall to accept 1,500 degree F tubing in the cabin.
   3. The rubber gasket sealing the front trunk from the under cowl/battery area is intact and functional.
   4. The access to the fuel pump is completely sealed by the battery carrier.
   5. The opening for the heater hoses behind the battery is sealed.

2. The allowance for penetrations of the engine compartment firewall for Caymans to allow engine cooling air to enter, or heated engine air to be removed is amended to allow that air can also pass through the body via an opening in the rear window (if class rules allow a plastic rear window) or through the sheet metal of the rear hatch below the rear window.

Proposal For Comment

10) 911 CUP / SP911 PERFORMANCE BALANCING

1. When 911Cup cars prepared to the SP911 specifications race east of the Mississippi, they must add 75 pounds to their minimum weight.
2. When 911 Cup cars prepared to the modified Stock specifications race west of the Mississippi, they may subtract 75 pounds from their minimum weight.

Please comment on this proposed change, which was not included in the original request for comment by November 15.  Unlike the first nine approved changes, which are subject to change only where significant errors in the underlying facts or reasoning are found, or to correct ambiguities, 911 Cup drivers are encouraged to comment on this change. It is intended to balance performance between the two rules sets for 911 Cup with a minimum of actual change. It is based on testing of lap times with weight removed from an SP911. No one wishing to race in the West has to lose weight – that is permissive. SP911s running East will have to add weight if they need to do that to make the higher weight for 911 Cup, or they can run SP911. This compromise is due to the belief that a significant number of 911 Cup drivers in the east do not want to have to lose more weight in order to remain competitive on the tracks they usually run, and that the SP911s were promised when merged into 911 Cup that their basic rules would not be changed.