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The 1966 Pontiac Grand Prix combined Pontiac's full-size performance hardware with a quieter personal-luxury identity. Every car used the 26657 two-door hardtop body on a 121-inch wheelbase. Wire-mesh grilles, rectangular parking lamps, stacked headlamps, GP fender emblems, ribbed lower panels and a full-width rear treatment separated it from the other big Pontiacs.
The standard four-barrel 389 made 333 gross horsepower with a manual transmission or 325 with Turbo Hydra-Matic. A 256-hp regular-fuel 389 was available with the automatic. Pontiac dropped the 389 Tri-Power for 1966, but buyers could still order a 338-hp four-barrel 421, a 356-hp Tri-Power 421 or the 376-hp 421 HO. Those engines are configurations of the same Grand Prix page. A car needs its PHS billing history and matching physical evidence before an optional-engine claim is treated as original.
A synchronized three-speed was standard. Wide- and close-ratio four-speeds and Turbo Hydra-Matic were optional. Pontiac paired them with a semi-floating Salisbury axle and power-team-specific ratios; Safe-T-Track was optional. Independent front suspension, a four-link coil-spring rear and 11-inch drums were standard, with power brakes, heavy-duty suspension and aluminum eight-lug hubs and drums on the option list.
New Strato bucket seats and deeply piped Morrokide led the 1966 cabin. Factory body-plate references document black, turquoise and slate Grand Prix trim families. The exterior palette contained 16 regular colors, and the options list extended from a Cordova roof to air conditioning, power accessories and instrumentation.
Pontiac built 36,757 Grand Prix cars for 1966. A reviewed production reference reports 917 with manual transmissions but does not divide three-speeds from four-speeds or publish a trustworthy engine split. Authentication therefore starts with 26657 identity and a car-specific PHS record, then checks the engine, induction, transmission, axle, paint, trim and component dates.