"LS engine" is the colloquial name given to the third and fourth generation small-block V8 gasoline engine used in General Motors' vehicles. The name evolved from the need to differentiate the Gen 3/Gen 4 small blocks from the original Gen 1/Gen 2 small blocks released in 1954, which are commonly referred to as "Small Block Chevrolets". The "LS" name originates from the engine RPO code of the first Gen 3 small block, the LS1, introduced in the 1997 Corvette. The term "LS engine" is used to describe any Gen 3 or Gen 4 Small Block Chevrolet engine, including those that do not specifically include "LS" as part of their RPO code. Sometimes referred to as an "LSx", with the lower case "x" standing in for one of the many RPO code variations of the motor, the term can cause confusion since GM now sells an aftermarket LS cylinder block named "LSX" with a capital "X". The original RPO code "LS1" is still sometimes used, if not confusingly, to describe the entire Gen 3/Gen 4 engine family. LS engines were a clean sheet, modular design. Most components interchange between these Gen 3 and Gen 4 motors. When compared to the Gen 1/2 Small Block motors, LS engines share no interchangeable parts except connecting rod bearings and valve lifters. Likewise, GM's fifth generation "LT" Small Block engines take inspiration from LS engines, but have almost no interchangeable parts. All cars sold with LS motors were equipped with aluminum blocks, while most trucks received cast iron blocks. LS engines have several notable improvements over previous generations of small blocks. The lower section of the block incorporates deep side skirts along with 4-bolt cross-bolted main bearing caps and a structural cast aluminum oil pan. Nearly all LS motors were manufactured with high airflow aluminum cylinder heads, even in truck applications. The design uses long runner intake manifolds to enhance airflow within the engines operating range. These dry intake manifolds omit the coolant passages of earlier generations to minimize heat uptake in the air charge. They are made from a light weight yet durable nylon polymer. A large improvement was made to the ignition system by forgoing the camshaft driven distributor of the early small blocks in favor of valve cover mounted ignition coils, one for each cylinder. LS ignition timing is handled by the ECU via camshaft and crankshaft position sensors. GM engineered the