71 Buick GS Stage 1 DV-09 MBC. GM said all its 1971 muscle car models must run on low-lead, regular-grade fuel (91 octane), and meet stricter exhaust-emission standards. The edict reduced the compression ratio of the GS 455’s V-8 to 8.5:1, from 1970’s 10.0:1. Horsepower tumbled along with it, to 315, from 350. The extra-cost Stage 1 package dropped two full points of compression and suffered a decline to 345 bhp from 360.