by chappyman66 » Tue Jan 09, 2018 10:10 pm
The "group" refers to the FIA classification of the cars and the associated rules.
The "Group 5" cars were ostensibly "production" cars underneath but managed to sprout huge engines and interesting aero aids.
The vintage Can-Am cars are sometimes called Group 7 because that was the FIA classification at the time.
The groups evolved and changed over time, so Group 5 cars from the 60s are different than the late 70s Gr5 cars that are popular slot cars today.