PRC Class Designations

Class designations for the PRC are meant to be simple, yet offer exciting and fair competition between racers.

For NASA-sanctioned events, the Porsche Racing Challenge Series includes a family of Grand Touring (GT) Classes, a Stock/Production Class, and a 911 “Spec” Class for Porsche 911 cars with a limited set of allowed modifications.

These classes are described in the Porsche Racing Challenge Series Rules:
For events sanctioned by the PCA, PCA Club Racing classifications will be in effect.

PRC Rules

The entire rules document can be downloaded via the link below:
2018 PRC Rules and Racing Mid Year Revision (PDF)

SPEC 911

Mike Cullinan, Corkscrew at Laguna Seca

Spec 911 is a class pioneered by PRC and now accepted nationally by SCCA and PCA. It is the most popular class in PRC. Spec 911’s are 50%+ of the entrants in a typical race weekend with up to 30 cars in the class. There’s good reason for the popularity of this class; the cars are fun to drive and embody the wonderful sounds and visual excitement of air cooled 911’s.

The entire set of rules governing Spec 911 are available in the PRC rules document, but in summary here are the requirements:

Chassis: 911 Porsche from ’69 to 89, no turbo.
Tires and wheels: Hoosier R7 and Hoosier H20
Front:  205×45/16 or 225×50/16 tire on 7 x 16 wheel
Rear:  245 x 45/16 tire on 8 x 16 wheel
Engine: Either 3.2 with stock induction or 3.0L with free induction. Long block must be stock.
Transmission: Stock 915 or G-50 (see gear ratios in rules)
Brakes: Free


Alan Austin At Laguna Seca

GTL is another spec class for race prepared air cooled 911’s that is rapidly gaining in popularity. Compared to Spec 911’s, GTL cars have bigger engines, wider tires and have more freedom for modifications. In power weight and grip, GTL cars are very similar to the legendary ’74 and ’75 Porsche RSR factory race cars.

The entire set of rules governing GTL are available in the PRC rules document, but in summary here are the requirements:

Chassis: 911 or 914 up to 1995
Tires and wheels: The GTL Class will use the following Hoosier Radial Slicks:
Front Part Numbers: 43656 (23.5 x 11 x 16, R75A compound or alternatively 43661 (23.5 x 12 x 16, R75A compound).
Rear Part Numbers: 43672 (25.5 x 12.5 x 16, R75A compound) or alternatively 43677 (25.5 x 14 x 16, R75A compound).
Engine: Pre ’95 3.6 with stock throttle body
Transmission: Porsche factory case with Porsche synchros


Allen Wilt At Laguna Seca

GTU is another class pioneered by PRC sitting between Spec911 and GTL. Building off of the Spec911 specifications GTU offers a wider array of suspension and aerodynamic modifications as well as an increase in horsepower and open gearing.