The GM Performance Parts production based blocks are the right choice for street car rebuilds or to start your own mild engine project. They come in the same dimentions that you are already familiar with and are produced with the high level of quality that GM is famous for. Remember, these are brand new castings machined to our exacting tolerances. These blocks are designed for street engines that demand good strength and a high level of durability. The 502 block has siamesed cyylinder bores, and the 454 block does not. Both blocks has 4 bolt main caps secured by grade 8 bolts. Both blocks have a 9.800" deck height. These production based blocks are a great foundation for your serious street or drag car that makes between 350-500 H.P. These blocks are the same starting point for GM Performance Parts high performance crate engines.