General Motors LS-based small-block engine

The General Motors LS-based small-block engines are a family of V8 and offshoot V6 engines designed and manufactured by the American automotive company General Motors. Introduced in 1997, the family is a continuation of the earlier first- and second-generation Chevrolet small-block engine, of which over 100 million have been produced and is also considered one of the most popular V8 engines ever. The LS family spans the third, fourth, and fifth generations of the small-block engines, with a sixth generation expected to enter production soon. Various small-block V8s were and still are available as crate engines.

The "LS" nomenclature originally came from the Regular Production Option (RPO) code LS1, assigned to the first engine in the Gen III engine series. The LS nickname has since been used to refer generally to all Gen III and IV engines, but that practice can be misleading, since not all engine RPO codes in those generations begin with LS. Likewise, although Gen V engines are generally referred to as "LT" small-blocks after the RPO LT1 first version, GM also used other two-letter RPO codes in the Gen V series.

The LS1 was first fitted in the Chevrolet Corvette (C5), and LS or LT engines have powered every generation of the Corvette since (with the exception of the Z06 and ZR1 variants of the eighth generation Corvette, which are powered by the unrelated Chevrolet Gemini small-block engine). Various other General Motors automobiles have been powered by LS- and LT-based engines, including sports cars such as the Chevrolet Camaro/Pontiac Firebird and Holden Commodore, trucks such as the Chevrolet Silverado, and SUVs such as the Cadillac Escalade.

A clean-sheet design, the only shared components between the Gen III engines and the first two generations of the Chevrolet small-block engine are the connecting rod bearings and valve lifters. However, the Gen III and Gen IV engines were designed with modularity in mind, and several engines of the two generations share a large number of interchangeable parts. Gen V engines do not share as much with the previous two, although the engine block is carried over, along with the connecting rods. The serviceability and parts availability for various Gen III and Gen IV engines have made them a popular choice for engine swaps in the car enthusiast and hot rodding community; this is known colloquially as an LS swap. These engines also enjoy a high degree of aftermarket support due to their popularity and affordability.

The brainchild of Chevrolet chief engineer Ed Cole, the first generation of the Chevrolet small-block engine was first unveiled in the 1955 Chevrolet Corvette and Chevrolet Bel Air, both powered by the 265 cu in (4,343 cc) "Turbo-Fire." The 265 Turbo-Fire distinguished itself from other engines of the era such as Cadillac's 331 series of the late 1940s and early 1950s by reducing the size and weight of various components within the engine; a compact engine block combined with a light valvetrain gave the Turbo-Fire a 40 lb (18 kg) weight reduction compared to the inline-sixes (despite having two more cylinders) that initially powered the first generation of the Corvette, alongside a significant horsepower increase of 25%. This contributed to lowering the Corvette's 0–60 mph (0–97 km/h) from 11 seconds to 8.7.

Nicknamed the "Mighty Mouse," the Turbo-Fire soon became popular within the hot rodding community too, along with scoring wins in stock car racing. A larger version of the Turbo-Fire arrived in 1957, now bored out to 3.875 in (98.4 mm). This gave the new engine a total displacement of 283 cu in (4,638 cc); this newer version was dubbed the "Super Turbo-Fire." The Super Turbo-Fire was also the first engine offered with mechanical fuel injection. The top-of-the-line model produced 283 hp (211 kW; 287 PS), giving it a 1:1 cubic inch to horsepower ratio; this lowered the Corvette's 0–60 mph (0–97 km/h) to 7.2 seconds.

General Motors would produce more powerful and larger displacement iterations of the small-block, until stringent emission regulations in the late 1960s severely limited performance. The Malaise era (roughly 1973 to 1983), as it was known, saw some of the lowest horsepower figures in several muscle and or pony car engines. This included the Corvette whose power output dropped below 200 hp (149 kW; 203 PS) despite a displacement of 350 cu in (5,735 cc).

1992 saw the second generation of Chevrolet small-block hit the market in that year's Chevrolet Corvette in the form of the LT1 small-block. It featured a new ignition system, reverse-flow cooling (cooling the cylinder heads first), and new engine block, but the valvetrain and engine mounts were carried over in order to maintain a degree of compatibility with the previous generation. Other modifications such as a better flowing intake manifold and cylinder heads gave the LT1 a power output of 300 hp (224 kW; 304 PS). The second generation culminated in the LT4 small-block, which gained a minor power increase of 30 hp (22 kW; 30 PS). Other changes included a lighter valvetrain and strengthened crankshaft.