A stock 1978 Trans Am 400 typically produced between 180 and 220 horsepower depending on the specific carburetor and other factory options. However, with significant engine modifications (forged internals, high-performance camshaft, high-flow heads, upgraded intake and exhaust, forced induction, etc.), a 400 cubic inch Pontiac engine can easily surpass 400 horsepower, and with extensive and expensive modifications, even 500 horsepower or more is achievable. However, reaching those higher figures often involves significant compromises in reliability and drivability.
