 Engine performance began declining in 1971 when GM issued a corporate edict mandating that all engines be capable of using lower-octane unleaded gasoline, which led to dramatic drops in compression ratios, along with performance and fuel economy.This, coupled with trying to build cars as plush as GM's more luxurious Buicks and Oldsmobiles, contributed to the start of a slow decline of Pontiac in 1971.In mid-1971 Pontiac introduced the compact, budget-priced Ventura II (based on the third generation Chevrolet Nova).