1969 Buick GS 400 Stage 1 original vintage advertisement. Stage 1 begins with a specially modified GS400. Those hood scoops are completely functional. They ram cool, clean air into the carburetor. The 400 cubic inch displacement remains the same. Increased output comes from a high-lift camshaft, a low-restriction dual exhaust system with a bigger, 2½ inch tailpipes, and a modified quadra-jet four-barrel carburetor with bigger throats. No wonder Buick owners keep selling Buicks for us.