Trophée de l'Avenir / Trophée Trans Europe
When the ETCC in the seventies came adrift, alternatives were needed. Paul Frère and Spa-Francorchamps started out in 1974 with rules somewhere between group 1 and Group 2. When, in 1976, the new Group 2 took over some of these rules were taken over - but not all.
A short impression of the rules:
"In the engine, mechanical parts may be machined within the limits and tolerances prescribed by the FIA, although additional materials or parts are not allowed. However, crankshafts, flywheels and camshafts may not be modified or lightened, and the same applies to what are called "component" parts of the engine.
There is no restriction on the gear or differential ratios used, but the number of gears must be as in a full Gp1 saloon car, and both the gearbox itself and the differential casings must be standard. Water radiators must be standard sized, but the addition of an oil cooler or radiator is allowed, and the thermostat may be removed.
Disc and drum brakes may be changed, so long as the surface friction area remains the same, but drums may not be replaced by discs. Although spring rates are free, the principle of suspension employed and its mounting points must remain absolutely unmodified. Wheel and tyre sizes are free provided that the wings project over them and the wheel arches are standard. The wings themselves may be extended for up to 5-centimetres on each side of the normal bodyline, and a spoiler may be fitted at the front below the centre line of the wheel provided it does not protrude beyond the normal perimeter of the car when seen from above.
Finally, the weight of the car as it crosses the finish line must still be at least that stated in the official FIA homologation form for a Gp1 car."
After 1975, group 1B was the next alternative, for Group 1 cars with a little extra. Since the Benelux countries, France and Great-Britain all had their own thoughts about what was legal and what was not, an international competition was nearly impossible - but tried nontheless.
Since the Spa 24h was always the center, I've listed what I found so far. A near-complete championship in 1975, mostle less for other years.
Group 1 alternatives