The LS1 and LT1 are both popularly known GM engines. The LS1 engine is just an improved version of the LT1 engine, and the major difference between them is the material used in making the block. The LT1 engine was made with cast iron, while the latter made LS1 engine is made with aluminum. Though some LS1 engines are still made with cast iron because they are meant for trucks, durability, and strength.
The LS1 engines, which are made with aluminum, are lighter and of better performance than the LT1 because of the difference in the materials used in manufacturing them. The LS1 also dissipates heat than the LT1. The earlier manufactured LT1 engines are of 260hp, while the LS1 engines are of 345hp, and still increasing. Thus, the LS1 engines produce more power than the LT1 engines. The LS1 engines system are distributors, while the LT1 engines are not.