The GTU was under 2 liter if I recall. They were 4 cylinder and rotory engined cars.
The GTO was V8, V6 and turbo cars
The GTP and GTP light were different in engine and chassie size.
The GTU Fiero was the first car other than a RX7 to win in that class and the only American car to win in that class. The Fiero was the first American champ in the GTU class.
Keep an eye out as some of these cars are raced in some vintage event yet today and some small road racing classes.
The neatest car was the GTO Fiero. It ran only some races in 1987 and won it first time out. It ran a Chevy 90 degree V6 in a non transverse location. It GM had not pulled the plug who know where it would have gone. It was the smallest car in a field of Mustangs and Camaros.
The GTP light cars went on and raced as Firebirds in the GTP class. One was also used by Computech to win the GTP light class and many races with a Acura engine in it.
GTO Fiero picture courtesy of RED GT
[This message has been edited by hyperv6 (edited 02-23-2005).]