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 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, and LS or LT engines have powered every generation of the Corvette since. 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.
Background
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 "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 weight reduction compared to the inline-sixes that initially powered the first generation of the Corvette, alongside a significant horsepower increase of 25%. This contributed to lowering the Corvette's 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. This gave the new engine a total displacement of ; 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, giving it a 1:1 cubic inch to horsepower ratio; this lowered the Corvette's 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, 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 despite a displacement of.
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, 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. The second generation culminated in the LT4 small-block, which gained a minor power increase of. Other changes included a lighter valvetrain and strengthened crankshaft.
The decision to stick with pushrod technology was seen as archaic at the time; such engines were seen as outdated compared to the smaller capacity overhead cam engines favored by European and Asian manufacturers. One of GM's domestic rivals, Ford, had announced plans to axe its small block engine from production in the early 1990s, in favor of its Modular engines. Another domestic rival, Chrysler Corporation, had stopped building passenger cars with V8 engines years prior, relegating them to its trucks and SUVs. Many car enthusiasts also desired a dual overhead cam engine; GM in response had developed the Northstar engines for Cadillac, but those engines were initially exclusive to that brand and not originally designed for rear-wheel-drive vehicles. Later on, Sam Winegarden, former General Motors chief engineer for small-blocks, stated that despite the stigma of the pushrod engine being "a symbol of the uncompetitiveness of the domestic industry," the decision to stick with pushrods was made on the basis that switching to overhead camshafts was unnecessary. The power requirements for the Corvette were satisfied by simply increasing engine displacement. Current General Motors chief engineer for small-blocks Jake Lee also stated that switching to overhead camshafts would also increase the height of the engine by, rendering it too tall to fit under the hood of the Corvette.
Approval for the Gen III was granted in May 1992, after a seat-of-the-pants decision made by General Motors executives who went for a drive in two Corvettes—one equipped with a traditional pushrod engine and one with a newer dual overhead camshaft engine. Tom Stephens, then-executive director of General Motors Powertrains, was the man in charge of the project. Stephens had the task of designing an engine that was not only more powerful than the previous small-block iterations, but one that could also deliver better fuel economy and meet emissions standards. Work began in 1993, shortly after the release of the LT1 Gen II engine. A small team hand-picked from the Advanced Engineering department of General Motors was assembled to do much of the initial design work, with initial prototypes hitting test benches by the winter of 1993. Stephens also recruited Ed Koerner, a former NHRA record holder, to help with much of the hands-on work, while Stephens focused on project management issues.
Design
All three generations are overhead valve engines, otherwise known as pushrod engines. Overhead valve engines have the valves mounted above the cylinder head, with a pushrod and rocker arm allowing a block-mounted camshaft to activate the valves. The advantages of an engine configuration like this is that since the camshaft is located within the engine valley, a pushrod engine will be shorter in height compared an overhead camshaft engine. Another advantage is that there are fewer mechanical components such as timing chains and extra camshafts, which increases reliability by keeping the engine simple.File:Pushrod2.PNG|thumb|A pushrod configuration that would typically be found in a LS-based overhead valve small-block. Lobes of a rotating camshaft transmit upward motion through valve lifters to pushrods, which open valves via downward motion transferred to them by a rocker arm.
All three generations were outfitted with either aluminum or cast iron engine blocks, with all passenger car engine blocks being aluminum, whereas truck engine blocks could be either material. Every single engine was also fitted with aluminum cylinder heads, except for the 1999 and 2000 model year of the LQ4, which were cast iron. Other modifications to the cylinder heads included a redesign to include significantly better airflow, with evenly spaced exhaust and intake valves. A deeper engine skirt meant that the third and following generations were slightly larger than its predecessors; the deeper skirts strengthened the block and improved rigidity. A deep engine skirt refers to an engine block which extends below the centerline position of the crankshaft within the engine. Another feature across all generations was the bore spacing and pushrods, the former of which is also in use in the Chevrolet Gemini small-block engine. The use of aluminum allowed for further weight reduction; the 1997 LS1 was almost lighter than previous cast-iron small-block iterations. GM also made extensive use of economies of scale for the LS: with the exception of the 4.8L and 7.0L engines, all variants used the same 3.622" stroke, the 4.8L and 5.3L variants utilized the same block casting, and several variants used the same length connecting rod.
Other modifications include long runner intake manifolds, powder-forged connecting rods and the introduction of six-bolt main bearings. Long runner intake manifolds in the LS series increases the airflow into the cylinders at low revolutions, increasing torque production at lower revolutions. Truck applications of the LS engine have even longer intake manifolds, being approximately taller than passenger car manifolds. Most engines were also fitted with hypereutectic pistons, replacing the previous cast pistons which were weaker and less thermally stable.
Powder-forging involves sintering a specific mixture of metals and non-metals which have been compressed in a forming press. The mixture is then quickly transferred into a traditional die cavity in a forging press and is pressed once then cooled. Powder-forging is also more cost-effective compared to traditional die forging, reducing the amount of tooling required to trim inconsistencies in hot-forged connecting rods. Stronger than the forged steel connecting rods of the previous two generations, powder-forged connecting rods have been fitted to every LS and LT engine except for the LS7.