What was the optional high-performance engine in the 1970 Buick GSX?

The optional high-performance engine in the 1970 Buick GSX was the 455 Stage 1. The GSX was based on the Buick GS 455 and came standard with a 455-cubic-inch V8; buyers could select the Stage 1 version for additional performance hardware and tuning.

The 455 Stage 1 used specially machined cylinder heads with larger valves, a more aggressive camshaft, a tuned Rochester Quadrajet four-barrel carburetor, revised ignition timing, and a higher numerical rear-axle ratio. Buick rated it at 360 horsepower and 510 pound-feet of torque, although period engine ratings used the optimistic SAE gross standard.

The GSX was Buick’s answer to performance packages such as the Pontiac GTO Judge, Oldsmobile 4-4-2 W-30, and Chevrolet Chevelle SS. Production was limited: 678 GSXs were built for 1970, with 400 receiving the optional Stage 1 engine and 278 using the standard 455. The 454 LS6 was a Chevrolet engine, while Buick’s relevant performance engine was its own 455.