Group N
In relation to motorsport governed by the FIA, Group N refers to a set of regulations providing 'standard' production vehicles for competition, often referred to as the "Showroom Class".
This contrasts with the Group A all-out competition production-derived vehicles. Group N cars are limited in terms of modifications made from standard specification. Group N was introduced by the FIA in 1982 to replace the outgoing Group 1 as "standard touring cars".
To qualify for homologation, a minimum of 2500 cars of the competing model have to be built in one year, out of 25,000 for the entire range of the model (eg: 2500 Subaru Impreza WRX, out of 25,000 Subaru Impreza).
Road racing
While Group A became the standard category for international touring car racing, Group N found a home as a more economic class in national touring car racing. In many countries, there were would often be two touring car championships, one for Group A and one for Group N. The category had some brief success with the demise of the Supertouring class in the late 1990s, when a few national regulations were relaxed to allow a greater number of modifications, in the guise of "Superproduction".
The category is still used in circuit racing all over the world, notably in Japan who has the long running Super Taikyu (Super Endurance or prounced as Suupaa Taikyu, スーパー耐久), as well as in the Italian ETCS endurance series run by Peroni Promotion, but was once again relegated to a secondary status with the introduction of Super 2000, the class of cars currently run in the World Touring Car Championship. The WTCC cars are based on "Superproduction" Group N, but have a greater degree of modification and are closer in spirit to Supertouring.
Rally Racing
In Rallying, the Production World Rally Championship is run under Group N rules. The cars used were modified road cars, often based on turbocharged, four wheel drive versions of standard small cars such as the Subaru Impreza WRX and the Mitsubishi Lancer Evolution, although a wide range of vehicles is homologated by the FIA for use in Group N.
The range of modifications allowed is quite narrow - few mechanical engine modifications are allowed (save for lightening within set limits and baffled sumps) although the choice of ECU is free, and this can liberate some extra power itself, and most of the modifications allowed are to promote longevity rather than increased performance, although the boundaries of these two areas are blurring.
Originally, Group N meant that all the interior trim had to be present (including the rear seat), whereas this has now changed to allow removal of the trim aside from the dashboard and replacement of the door trim. The springs and dampers are free, as are the internals of the gearbox, providing that the homologated gear ratios and gearchange pattern are respected. This allows the use of 'dog' engagement gearboxes, providing quicker gearchanges and longer gearbox life. There is provision for strengthening of the suspension components and bodyshell, providing this doesn't alter the operating principle.
The FIA and many national motorsport associations are moving towards making rallying championships based in Group N, in an attempt to reduce costs, reinforce the link between motorsport and the car that the member of the public drives, and to reduce the environmental impact of motorsport.