 Inside, new high-back Strato bucket seats with built-in headrests replaced the 1970-only low-back seats with adjustable headrests.The biggest changes came under the hood, due to a GM-corporate mandate all engines be designed to run on lower-octane regular-leaded, low-lead, or unleaded gasoline, necessitating reductions in compression ratios and horsepower ratings.The straight-6, V8, and two-barrel V8 were virtually unchanged, as they were low-compression regular-fuel engines in 1970 and previous years.