Formula package — blacked-out grille, front air dam, body-color rear spoiler, Rally wheels, lower-quarter "FORMULA" striping

Years 1969–81 Models 2

Also described as 400 4-bbl (Firebird 400)Formula (model option RPO)Formula package — handling package, three-piece spoiler, decals, chrome valve cover, T/A steering wheel

Documented applications

Firebird / Trans Am

1969 Confirmed

Same UPC later = Astre/Sunbird Formula package
1970s–1981 Single-source

Per Trans Am Country model-RPO list; W67 = Esprit

Ventura / Astre

1977 Confirmed

Astre coupe/hatchback; ~350 built
1977–1980 Confirmed

Coupe from ’77 (hatchback added Mar ’77); coupe+hatch ’78–79; hatch only ’80

This page aggregates every documented appearance of W66 in the Pontiac reference. Confidence and citations are shown per application — the same code can be better documented in one year than another.