The difference between a long block and short block engine is the number of parts these components contain. Neither of these engine components are fully complete, and a short block engine has fewer parts than a long block engine.
A short block engine is not complete, but each engine does have connecting rods, cam pistons and a crank. These engines require additional internal parts such as cylinder heads, an oil pump and gaskets. Some short block engines come with timing parts and camshafts. A long block engine is almost complete, but it requires the installation of additional external parts including manifolds for the intake and exhaust, valve covers, and oil pan and timing covers.
There is potential for better car engine performance from a long block engine than a short block due to the installation. Since there are more parts in a long block, there are fewer issues that can arise during installation. However, a short block engine allows a car owner to have more choice, and these choices could benefit performance. If a short block engine requires a replacement, it indicates that some of the major parts have damage that is irreparable. Fortunately, it is possible to install many parts of a short block engine, such as the heads, intake and exhaust manifold, to a new short block.