The easiest way to tell without even opening the hood is as follows:
If it's one of the older "four eye" cars (that is, it has the sealed beam headlamps on it), if it's a Turbo Coupe it will have fog lights or at least spaces for them in the front bumper. V6 and V8 cars didn't have the fog lights. Also these cars were not intercooled so there was no scoops in the hood.
If it's an '87 or '88 with the "aero" headlamps, and it has a chrome grille, it will be a V6 or a V8. Turbo Coupes had a special "grille-less" front fascia and also had fog lights in the front bumper.
That should help because those are the most distinguishable features of the cars. Based on what you've said so far, it sounds to me like it's probably an '83-86 car.