Following Pontiac’s lead with the 1964 GTO, Buick introduced its own mid-sized muscle machine in 1965: the Skylark Gran Sport.

When Pontiac scored a surprise sales hit in 1964 with the GTO, the entire Motor City stood up and took notice. That included Pontiac’s rival division at General Motors, Buick, which until then had little presence in the youth and performance market. But Buick product planners could see that by tracing the GTO template—the GM A-body intermediate platform combined with a big V8 and other performance gear—they too could cash in. The Skylark Gran Sport was launched in January of 1965 as a mid-year model. A few months earlier, Buick had introduced the Gran Sport badge on a sporty version of the luxury Riviera.

Buick’s classic Nailhead 401 cubic-inch V8 was a tight fit in the Skylark’s engine room, as a new oil pan, oil pump, and exhaust manifolds were required to squeeze it in, and with power steering and air conditioning (above) there was little room left. At 685 lbs, the old-school V8 was also considerably heavier than either the Buick V6 or the 300 CID V8, the Skylark’s usual powerplants. Car Life mgazine measured the Gran Sport’s front/rear weight distribution as 58.3/51.7 percent.

There was another issue, too: a GM corporate decree that A-body intermediate cars couldn’t have engines of greater than 400 cubic inches. The workaround was simple enough. The 401 V8 (401.4 CID, to be exact) would be declared a 400 in the Gran Sport for marketing purposes, and the GM brass on the 14th floor approved. With a Carter AFB four-barrel carb and 10.5:1 compression ratio, the trusty Nailhead was rated at 325 hp at 4,400 rpm and 445 lb-ft of torque at 2,800 rpm—respectable figures for the muscle class. (See our feature on the Buick Nailhead V8 here.)

The Gran Sport could be had as a two-door post sedan, a hardtop coupe, or a convertible. However, all three were built on the heavier convertible frame to cope with the added power and weight. A floor-shifted three-speed manual gearbox was standard, while the Muncie 4-speed and two-speed Super Turbine automatic were extra-cost options. Heavy-duty shocks. stiffer springs, a fat front stabilizer bar, and Gran Sport emblems rounded out the package, which was priced competively with the GTO and the Oldsmobile 442.

Most all the major magazines of the time got a shot at the Gran Sport, including Hot Rod, Motor Trend, Car Life, and on the East Coast, Cars. All were complimentary, though the Motor Trend reviewers wondered why a limited-slip rear axle wasn’t included given the Gran Sport’s nose-heavy weight distribution. Car Life even suggested that most buyers would be better off with the V6 instead of the hefty Nailhead. The Gran Sport received a lighter, more modern 400 CID V8 in 1967, and it truly came into its own with the 1970 455 Stage I V8.