#36881 2025 Prototype (P) Ruleset

Cars must comply with GCR section 9, Cars and Equipment. Brake lights are not required.
B. CHASSIS
1. Any form of chassis construction is permitted, subject to the requirements of GCR section 9, Cars and Equipment.
2. Anti-intrusion panels are permitted anywhere on the sides of the chassis. Materials and attachment are
unrestricted.
3. Cars may be either single-seat or two-seat cars, subject to restrictions in these rules.
4. Closed-cockpit single-seat cars are not permitted unless specifically allowed by a spec line in Table 1.
C. BODYWORK
1. The bodywork must provide safety and comfort for a driver and passenger in two-seat cars and for a driver in
single-seat cars. All elements of the bodywork must be completely and neatly designed and finished, with no
temporary or makeshift elements.
2. The bodywork as viewed from the side and above must cover all mechanical components including suspension,
except that the intake, exhaust, tow hooks, jack points, and radiators may be exposed. As viewed from the side,
the bodywork must extend over the full width of the tires for at least one- third of their circumference. Louvers
to extract air from the tops of the fenders are permitted. Tires must not be seen as viewed from above except
through louvers; the fore/aft opening through which a tire may be seen must not exceed 5mm (0.197 inches)
when viewed from above. Rear tires may be exposed as viewed from the rear. Cycle-type fenders that cover only
the tire and are not continuous with the bodywork are prohibited. Fenders must be firmly attached to the
bodywork.
3. Height: No part of the car having special or significant aerodynamic function may exceed a height of 115cm
(45.275 inches) above the ground with the car in normal racing trim, driver aboard. As viewed from the side,
the outermost surface of bodywork between the front and rear wheel openings and above the floor must have
a minimum height equal to the height of the front axle centerline.
4. Width: The maximum width must not exceed 221cm (87 inches) including all aerodynamic devices. No part of
the bodywork may extend outwards more than 10cm (3.937 inches) beyond a vertical plane connecting the
outermost surfaces of the front and rear tires. The minimum body width between the front and rear tires as
viewed from above may extend inwards beyond a vertical plane connecting the centerlines of the front and rear
B. PROTOTYPE (P) CLASSIFICATION
tires for a distance of up to 20% of the length of the wheelbase.
5. Length: The maximum overall length is 485.3cm (191 inches).
6. Cockpit:
a. The driver’s seat must be capable of being entered without the removal or manipulation of any part or
panel other than a removable steering wheel and removable padding. This requirement does not apply to
doors on closed-cockpit cars that are specifically permitted by these rules.
b. The cockpit opening must comply with the following dimensions for both single-seat and two-seat cars:
minimum cockpit length is 60cm (23.622 inches) and minimum cockpit width for each seat is 45cm (17.717
inches) maintained over 30cm (11.811 inches). The minimum rectangular opening may be measured
anywhere forward of the main roll hoop. Roll hoop or roll cage braces, required padding, and removable
helmet surrounds are not to be included in this measurement.
c. For two-seat cars, there must be room for seats of equal dimension and comfort for the driver and a
passenger equally disposed on each side of the longitudinal axis of the car. The seats must be firmly
attached in the car but may provide adjustment for the size of the occupant. The body surrounding the
driver and passenger compartment must be symmetrical about the longitudinal axis of the car. The
passenger’s space and seat must remain usable throughout the competition and must not be encroached
upon by an element of the car or equipment except as provided in these rules. Permitted equipment
includes batteries, ballast, fire bottles, data-recording devices, and cool suit equipment, provided that such
equipment is securely attached to the car.
7. The bodywork must give the driver visibility forward and to both sides adequate for racing conditions, and
rearview mirror(s) must give the driver visibility to the rear of both sides of the car.
8. Windscreens are optional.
9. Brake ducts and ducts allowing air into the engine compartment are permitted.
10. Engine air intake ducts, scoops, and cold air boxes are permitted.
D. AERODYNAMICS
These rules are intended to control the use of “ground effects” to achieve aerodynamic downforce.
1. Aerodynamic devices must be securely mounted on the entirely sprung part of the car and must not be movable when
the car is in motion.
2. Aerodynamic devices (e.g., “skirts,” body sides) must not extend more than 1cm (0.394 inches) below the car’s lower
surface at any point behind the front axle. Seat buckets or other protrusions must not circumvent this rule.
3. All ducted air that exits through the top of the bodywork behind the rear of the front tires must pass through a heat
exchanger. This requirement does not apply to the cockpit opening, fender louvers, or slots, grills, louvers, and similar
devices intended to allow heat to escape the engine bay.
4. Air must not be ducted through any part of the bodywork for the purpose of providing aerodynamic downforce on the
car. This prohibition includes openings above the front spoiler or splitter that permit air to pass through the front
bodywork for the purpose of providing aerodynamic downforce.
5. Body panels intended to cover suspension components as viewed from the side and above must not be shaped as an
airfoil cross-section. Upper and lower panel surfaces must be symmetrical (mirror images) across a straight line
connecting the center of the leading edge with the center of the trailing edge. Leading and trailing edges may be rounded.
Panel angle front to rear and side to side is unrestricted, but panels may not be used to provide additional aerodynamic
downforce on the car.
E. WHEELS AND TIRES
Wheel size is unrestricted except for a minimum diameter of ten inches. Wheel sizes must be identical for the right-front and
left-front axles and identical for the right-rear and left-rear axles. Right-front and left-front tires must be the same size and
right-rear and left-rear tires must be the same size.
F. BRAKES
1. Cars must be equipped with a dual-braking system operated by a single control. In case of leak or failure at any point in
the system, effective braking power must be maintained on at least two wheels.
2. Brake calipers may be ferrous or aluminum alloy. Effective 1/1/2026, carbon-carbon and carbon-ceramic brake rotors are
prohibited and rotors must be ferrous.
G. BULKHEADS AND TANKS
Fuel tanks must be isolated by means of bulkheads and vented so that in case of spillage, leakage, or failure of a tank, fuel and
fumes will not pass into the driver or engine compartment or around any part of the exhaust system. No part of any oil or water
tanks may be exposed to any part of the driver or passenger compartment. Safety fuel cells (per GCR section 9.3 Fuel Cell
Specifications) are required for all cars.
H. TRANSMISSIONS
All gear changes must be initiated by the driver. Mechanical gear shifters, direct-acting electric-solenoid shifters, air-shifters,
and similar devices are permitted. Electronically controlled differentials and devices that permit pre-selected gear changes are
prohibited. Power must not be applied to more than two wheels. Traction control is prohibited.
1. Cars with automotive-based engines may use any manual transmission up to six speeds with reverse.
2. Cars with motorcycle-based engines must use the transmission supplied with the engine; a reverse gear is not required
for cars using motorcycle-based engines.
I. DATA COLLECTION
All cars competing in the U.S. Majors Tour and the Runoffs must have the AiM part #X47KPF-SOLO2R0 data box mount installed
to provide the necessary mounting of the AiM Solo 2 data box. The mounting surface must be approximately oriented either
horizontally or vertically and either parallel or perpendicular to the longitudinal axis of the car and must be accessible from the
exterior of the car with the driver on board. The data box must have a view of the sky and must not be located under carbon fiber
or metallic bodywork. Sufficient space must be left between the mounting plate and the surface to which it is attached to permit
the use of zip ties/tie straps to restrain the data box to the mounting plate. The purpose of this requirement is to allow the
random placement of data boxes on cars on the pre-grid by SCCA-assigned personnel and the collection of the data boxes when
cars exit the racetrack. Contact AiM and its distributors for direct purchase of the data box.
J. ENGINE AND WEIGHT RESTRICTIONS
Generally applicable information for Prototype engines is given in the following paragraphs. The Engine Table below
provides general specifications of engine types, displacement limits, intake restrictions, and car weights. Specific
engines approved for use (along with applicable restrictions) are also provided in the table. All specified minimum
weights are with driver (GCR section 9.3 Weight).
1. Turbocharging and supercharging are prohibited.
2. Four-cycle engines may have a maximum of four cylinders. Two-cycle engines may have a maximum of six
cylinders.
3. Intake manifolds are unrestricted on engines that do not require a flat plate intake restrictor unless otherwise
noted in an engine spec line. Plenums and/or balance pipes are not permitted on engines that use an individual
runner-type manifold and require a flat plate intake restrictor.
4. Where a flat plate intake restrictor, restricted venturi, or Single Inlet Restrictor (SIR) is required, all intake air for
each cylinder or the entire fuel-air mixture, if prepared before this point, must pass through the restrictor.
5. SIR installations must comply with the requirements of Appendix F. Technical Glossary. Where intake restrictors
(except SIR) are required, the restrictors must be round orifices (unless otherwise specified) and located within
four inches of the throttle butterfly.
6. On four-cycle motorcycle-based engines equipped with individual throttle bodies, individual flat plate intake
restrictors must be installed within four inches of the primary butterfly throttle shaft or centerline on the intake
side of the individual throttle body’s primary butterfly. Restrictors may be mounted in any manner that does not
reduce the intended effectiveness.
7. Where a flat plate intake restrictor is required, fairings may be used above and below the plate to create an inlet
venturi. Compliance with the restrictor size specified will be measured in the round orifice of the flat plate intake
restrictor.
8. The SIR testing procedure in Appendix F. Technical Glossary (Restrictor, Intake) is modified as follows: If the engine
stalls within 3 seconds, the car is deemed compliant with the stall test.
9. The use of an ECU map, computer program, or any other artificial means to stall an engine at any time during the
SIR testing procedure in Appendix F. Technical Glossary (Restrictor, Intake) is prohibited.
10. Electronic throttle control systems (ETC, Fly-by-wire, Drive-by-wire) are permitted. ECUs that use ETC/FBW/DBW
throttles must have dual-output pedal position sensors (or other ECU-required fail-safes) that are capable of
detecting a fault and limiting throttle activation.
11. Cars must be equipped with an automatic starter and on-board power supply operated by the driver.
12. Cars must display their engine size from the applicable spec line and the size of their required restrictor, if any,
in a manner that is clearly legible to the scrutineers at the scales.
13. Engines not specified in the tables below are not permitted in Prototype. SCCA encourages members who wish
to race other engine designs or propulsion systems not listed below to request consideration on a case-by-case
basis via letter to the Club Racing Board at crbscca.com.
K. SPEC LINE CARS
Table 1 (Spec Line Cars) is intended to accommodate existing cars that were previously raced in CSR, DSR, S2, or P2
without requiring expensive changes to make them compliant with the Prototype rules.
For individual cars included in any of the spec lines in Table 1, any deviation from the spec line and column
requirements requires the car to be made compliant with all current Prototype requirements with a notation in the
front of the logbook noting the requirement for the car to be compliant with all Prototype rules.
P2 cars may compete in either the Prototype class or the P2 class but must participate in the Prototype class to the
extent necessary to qualify for an invitation to the Runoffs in Prototype.
Prototype Engine Table