For the 1967 model year of the GTO, Pontiac discontinued the infamous 389 tri-power setup and introduced a 400-cid engine. The reason behind this was due to a corporate policy change banning multiple carburetors for all cars except for the Corvette. This meant the highly feared tri-power set up was replaced with a Quadra-jet 4 barrel carburetor. The 389 block received a slightly wider cylinder bore (4.12 inches, 104.7 mm) for a total displacement of 400 in (6.6 L). Torque also increased slightly, from 431 to 441 ft-lb. for the base engine, and 424 to 438 ft-lb. for the upgraded HO (High Output) engine. The base engine featured a four-barrel carburetor, which was rated at 335 horsepower. For only $76.89 you were able to upgrade to the "YZ" "4BBL 400 HO HYD ENG" option. This upgrade added a higher-lift camshaft, free-flow exhaust manifolds, and an open-element air cleaner. The factory rated the High Output "HO" engine at 360 horsepower. Of the 81,722 GTO's built in '67, 13,827 were equipped with the HO engine. The HO engine is still very highly sought after and significantly raises the value of these classic cars in today's market. The easiest way to identify an HO engine is to look for the "YZ" engine stamp on the front passenger side of the block, also the HO exhaust manifolds, and the unique open element air cleaner.