Buick GS Stage 1_Gran Sport

1970 Buick GS (Grand Sport)
455 C.I. Stage 1

Wiki:
The 400 was replaced for 1970 with the 455 in³ Buick V8, used in the GS 455. The base model V8 produced 350 hp (260 kW) and 510 ft·lbf (690 N·m) at 2600 rpm. In the optional Stage1 trim it produced an underrated 360 hp (193 kW) and 510 ft·lbf (691 Nm) at a low 2800 RPMs. The real number was more accurately 415 hp (309 kW) to 425 hp (317 kW) due to the Stage 1 engine using a more aggressive cam and the standard heads were machined for larger valves to produce more power. The lower (false) horsepower numbers were used to get by General Motors Corporation imposed restrictions and Insurance Company concerns over increasingly powerful engines in affordable mid-size passenger cars, affectionately known as Muscle Cars. The Stage 1 option, when paired with an automatic, included a firmer shifting Turbohydromatic 400, and a standard 3.42:1 posi-traction rear differential. A 3.64:1 rear ratio was standard when delivered with a Stage 1 and manual transmission with optional gears available to at least a 4.33:1 ratio.

The relatively unknown and expensive when new 1970 GS 455 Stage 1 drew a great amount of attention and controversy in the muscle-car world when in the 1980's 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 controversy which continues today and has been a great boon to car magazine sales over the years.

There was also a very rare Stage 2 option produced. This was a dealer-installed package that was first offered in 1969 and included a cam, headers, intake manifold, high compression forged pistons, hollow pushrods, and some calibration changes to the ignition and carburetor. If the car was ordered with the Stage 2 package, the parts were shipped with the car but were installed at the dealership. In 1970(?) the Stage 2 package included special, round exhaust port Stage 2 heads, matching Kustom brand headers, a radical cam, high compression forged pistons, Edelbrock B4B aluminum intake, and other equipment for racing. Few stage 2's were ever used on the street and Buick only ever factory assembled 3 Stage 2 test units. One of which was a factory GSX test mule with 4 speed manual transmission used for speed testing. The Stage 2 package's existence was not made public until 1972 when the Stage 2 parts could be ordered in any combination. There is little documentation about the Stage 2 cars.

Output and sales for the assembly-line cars were down after 1970 largely due to reduced engine compression ratios and a change from gross to net horsepower ratings. In later years, air quality regulations further limited the power in part due to the addition of catalytic converters and single exhaust pipes. However, Stage 2 parts were available over the counter although the stage 2 heads were discontinued after about 75 sets were produced. The discontinuation was due to problems with castings.