The 1970 Buick GSX Stage 1 was factory-rated at 360 horsepower. This was the advertised SAE gross rating for Buick’s upgraded 455-cubic-inch V8, measured under the industry’s pre-1972 rating method.
Stage 1 was more than a badge. The engine received revised cylinder heads machined for larger valves, a more aggressive camshaft, higher-compression specifications, special carburetor calibration, and revised ignition timing. Buick also paired the package with performance and handling equipment, helping the GSX deliver strong acceleration and exceptional torque.
The horsepower figure can be confusing because SAE gross and SAE net ratings were not measured the same way. Gross ratings were taken with fewer production accessories and restrictions, while later net ratings better represented an engine as installed in a car. Some independent tests and engine-development accounts produced higher figures, but the official published rating for the 1970 Stage 1 was 360 horsepower.
The engine also produced 510 pound-feet of advertised torque at 2,800 rpm. That combination of a relatively conservative horsepower number and immense low-speed torque helped the GSX Stage 1 perform strongly against lighter and more famous muscle cars.