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401
The 401 in³ (6.6 L) 401 was Buick's muscle car powerplant of choice, and was found in the company's Skylark Gran Sport and Buick Wildcat, among others. As unlikely as it seems, the air cleaner for the engine is annotated with "Wildcat 375" "Wildcat 410" "Wildcat 445" these inscriptions indicated not the in³ but the ft·lbf. of torque produced by the engine. The "Wildcat 410" was the 2-barrel carburated engine that was standard on the 1962-63 LeSabre. The "Wildcat 375" was a no cost option on the 62-63 LeSabre that had lower compression to run on regular fuel (another Buick V8 had "Wildcat 375" written on its air cleaner but it wasn't a "Nailhead", it was the 4 barrel version of the 66-67 small block Buick 340). The "Wildcat 445" had a single 4 barrel carb. It was the standard engine on the Invicta, 1959-66 Electra, 1962-66 Buick Wildcat, 1963 Riviera and 1965 Riviera (the 64 and 66 Riviera models had a 425 in³ engine with a single 4 barrel carb. named "Wildcat 465" as standard equipment).
In an effort to overcome the "restrictive" exhaust port design, Buick enthusiast drag racers in the sixties adapted superchargers with a custom camshaft to feed intake air in through the exhaust ports and used the larger intake ports for exhaust outlets. Perhaps this feat of ingenuity, and the unusual appearance of the engine modified in this manner, also intimidated rival racers and added to the Nailhead V8 legend that lives upon this page of US auto history.
425
425 in³ (7.0 L) 425 This was the largest version of the "nailhead". It began as an option in 1963 on the Riviera and it was later available on the Wildcat and Electra models too. The 1964 and 1966 Riviera had the 425 engine as standard equipment. 4 barrel carburetion was standard on all 425 "Nailheads" that were called "Wildcat 465". The "465" sticker on the air cleaner did not denote engine displacement as many though, it denoted the torque rating. It was possible to order two 4 barrel carbs, which were delivered in the trunk along with the intake manifold and installed by the dealer. This version was called "Super Wildcat" and it was standard on the 1965 Riviera Gran Sport and the 1966 Wildcat GS.