page_title: Buick Gran Sport
section_title: Gran Sport 455
hierarchical_section_title: Buick Gran Sport / Skylark based Gran Sports / Gran Sport 455
caption_attribution_description: English: Buick GS 455 Convertible
context_page_description: The Gran Sport name has been used on several high-performance cars built by Buick since 1965. In the GM brands hierarchy, Buick was surpassed in luxury and comfort appointments only by Cadillac, which did not produce performance models. As a result, the Buick GS series were the most opulently equipped GM sport models of their era.
context_section_description: The 400 was replaced for 1970 with the Buick 455 cu in (7.5 L) V8 engine, used in the GS 455. The base model was rated at 350 bhp (355 PS; 261 kW) and 510 lb⋅ft (691 N⋅m; 71 kg⋅m) at 2800 rpm of torque. In the optional Stage 1 trim equipped with a single 4-barrel Rochester Quadrajet carburetor was rated at 360 bhp (365 PS; 268 kW) SAE gross at 4600 rpm and 510 lb⋅ft (691 N⋅m; 71 kg⋅m) at 2800 rpm of torque. As with all American engines produced prior to the 1972 model year, these were SAE gross ratings, which are generally significantly higher than SAE net ratings and are not indicative of what actual production engines produce in their "as installed" condition (with all engine accessories and full exhaust system in place).  The fastest magazine test results from this period were obtained by MOTOR TREND Magazine, which managed to extract a 13.38 ET at 105.5 mph from their 3,810 pound GS Stage 1 coupe test car. Using Hale's Trap Speed formula, this result indicated actual "as installed" peak HP of approximately 360 SAE Net (ironically the same as its advertised Gross Figure, meaning this engine was very conservatively rated for that time period).
  Dennis Manner, Buick Engine development engineer still recalls the production-line pulled engine dyno test results from 1970 where the lowest HP output of the 15 tested 455 Stage 1 engines was 376 hp.
  The December 2004 issue of Musclecar Enthusiast magazine conducted an engine dynamometer test of a freshly rebuilt and well documented 1970 455 Stage 1 (bored .040" over to 464 cubic inches and minus the power-robbing factory engine fan, air cleaner assembly and mufflers). In that condition and with factory timing and carburetor tuning, the engine produced a maximum of 360.9 HP. Optimal carburetor and ignition tuning yielded a peak HP reading of 381.7 HP - again with no engine fan, air cleaner or mufflers in place. While urban legend would have us believe that these engines made "420 HP from the factory," actual empirical results prove otherwise. Although another dynamometer test on a 1970 Skylark GS Stage I showed 471 SAE gross hp, which is more consistent with the engine producing about 360 SAE net hp.
  The Stage 1 engine option used cylinder heads that, while using raw castings of the same pattern as all of the other Buick 455s sharing the same model year, were machined differently in order to accept larger valves (2.13" intake and 1.755" exhaust), and to produce smaller compression chambers for increased static compression ratio. The option also included a more aggressive camshaft, a specially tuned 4-barrel Quadrajet carburetor, more aggressive ignition timing,5/8 inch oil pickup tube and a higher numerical final drive, and was available with either Turbo Hydra-matic 400 3-speed automatic transmission, or a Muncie M-22 4-speed manual transmission (although it was later discovered, and confirmed, that one 1970 GS Stage 1 convertible was produced with a 3-speed manual and a standard 3.64:1 Positraction axle ratio). Stage 1 cars equipped with air conditioning received a 3.42 axle ratio.
  While powerful in production form, the Buick 455 (including Stage 1) engines had problematic engine blocks. All used 2 bolt main bearing caps; the oiling system was undersized for high-rpm use (including Stage 1 engines) and thin walls in the lifter valleys promoted cracking. The magic of the Stage 1, it would seem, was primarily attributable to its advanced (for the period) cylinder heads, stunningly high torque and the relatively high mid-range horsepower they produced.
  The relatively unknown, very expensive, and very rare 1970 GS 455 Stage 1 drew a great amount of attention and controversy in the muscle-car world when in the 1980s it was listed as faster than any of the Chrysler Hemi cars in the original "50 fastest muscle cars" list. This Hemi vs. Stage 1 controversy has prompted several contests to settle the issue; it remains an unsettled matter and has been a great boon to car magazine sales over the years.
  There was also a rare “Stage 2” option produced. This was a dealer-installed package (
caption: Buick GS 455 convertible
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