The 1970 model year was the last before emissions regulations, insurance industry pressure, and fuel economy concerns began the systematic reduction of American muscle car performance. Chevrolet, aware of what was coming, produced the 1970 Chevelle SS 454 in the full knowledge that it represented a high-water mark that would not be repeated. The LS6 engine variant — 454 cubic inches, solid lifters, high-compression heads, and a factory rating of 450 horsepower that was understood at the time to be conservative — was the most powerful engine Chevrolet offered in a passenger car in 1970 and arguably the most powerful engine Chevrolet has offered in a passenger car since.