A-Spec and B-Spec are just terms for levels of modification. Also refered to as Group (Gruppe) A and Group (Gruppe) B.
FIA regulations mandate the modification levels on these different cars.
Every car that participates in Group A racing has to be produced to numbers above 2500 units. Group N is 5000 units, and Group B is the lowest, at only 200 units, based on how much they cost to produce, due to the very powerful nature of the cars in Group B.
Group A cars are similar, nowadays, as follows:
- 4 wheel drive transmissions
- 2 liter turbo charged engines (there's an FIA 1.7 engine displacement multiplication factor for turbo charged cars) using a 34mm turbo restrictor
- Front mounted engines (longitudinal or transversal)
- Minimum weight of 1230 Kg
- Active differentials
Group A allows for the following modifications by FIA regulation:
- Full suspension geometry and layout. The original mounting points must be preserved within a 20mm radius
- Engine internals including camshafts, crankshaft, valves. Other engine components can be machined. The engine block must be preserved
- Engine peripherals (Radiators, intercoolers, ...)
- Engine management
- Braking system
- Gearbox, gear ratios, number of gears and gear selection type
- Differentials
- Final drive ratio
- Electric equipment
As you can see, there are few limitations. Group N is a little more restricted, and Group B is a little less.
WRC cars are generally modified beyond Group A standards, as well, but fall into their own group. Hope this clears some stuff up. =)
Basically, A-spec, B-spec, and so on are just different names for car modification levels in racing, in summary.
