RPM through a single 3" catalytic converter. Easily verified through GM Heritage Center website. 1987-1990 Chevrolet C/K 1987 GMC Suncrest Commercial applications Mark IV engines saw extensive application in Chevrolet and GMC medium duty trucks, as well as in Blue Bird Corporation's All American and TC/2000 transit buses (the latter up until 1995, using a 427 with purpose-built carburetor). In addition to the 427, a version was produced for the commercial market. Both the 366 and 427 commercial versions were built with a raised-deck, four-bolt main bearing cap cylinder to accommodate an extra oil control ring on the pistons. Unfortunately, the raised deck design complicated the use of the block in racing applications, as standard intake manifolds required spacers for proper fit. Distributors with adjustable collars that allowed adjustments to the length of the distributor shaft also had to be used with 366 and 427 truck blocks. Mark IV engines also found themselves widely used in power boats. Many of these engines were ordinary Chevrolet production models that were fitted with the necessary accessories and drive system to adapt them to marine propulsion. Mercury Marine, in particular, was a major user of the Mark IV in marine drives, and relabeled the engines with their corporate logo. Generation V For 1991 General Motors made significant changes to the Big-Block resulting in the Generation V. The block received a one-piece rear seal and all blocks received 4-bolt mains. Additionally the main oil galley was moved from near the oil pan to near the camshaft. Also the valvetrain became non-adjustable and the provisions for a mechanical fuel pump were eliminated. Cast aluminium rocker covers were fitted in place of stamped steel covers, featuring a screw-in filler cap. Structural changes were carried out to the cylinder case to improve the integrity of the bores and the inlet manifold was changed to a single-piece design. 6.0 (L50) The truck engine also received the Mark V updates for 1991. L19 From 1991 the 454 was updated to the new Gen V block, crankshaft and heads. This engine was rated at 230 net hp, 380 ft lbs net torque, and was discontinued after 1995, GM coming out with the Vortec 7400 in 1996. 502 The 502—with a total displacement—had a bore and stroke of and a cast iron 4-bolt main block. GM offered it in their Performance Parts catalog, available as multiple crate motors with horsepower ratings