Jul 29, 2021 · 04: Most powerful. Unlike many of the GTO’s competitors, Pontiac never built a GTO with an output rating of over 400 horsepower. In fact, the most powerful production GTOs were the 1969–70 models with the optional Ram Air IV 400-cubic-inch V-8, which made 370 horsepower at 5500 rpm and 445 lb-ft of torque at 3900 rpm.