GS 400 — SERIES 44600 — Similar to the GS 350, the most potent Buick had 400 numerals on the hood scoop and rear quarters. A Deluxe steering wheel was standard, along with foam padded seats, ashtray light, glovebox light and upper interior light. Interiors were all-vinyl with a bench front seat standard and buckets available optionally. There was a unique GS 400 grille and a cold air induction package. A hot, dealer-installed option was the Stage 1 package including a 400-cid V-8 with 11.0:1 compression that was rated for 345 hp at 4800 rpm and 440 lb-ft of torque at 3200 rpm. Experts said the actual output of this engine was closer to 400 hp.