GM’s 55-Year Love Affair with the Small Block
There’s no denying the long, storied history of General Motor’s love affair with the fabled push-rod small block V8. While many today will contest that today’s stellar LS7 427 is no “small block” by any stretch of the performance-enthusiast’s imagination, the story arc of the engine’s creation, development and evolution is as interesting and compelling as anything pertaining to our hobby within the last half century.
Although a new engine was on the drawing table when Chief Engineer Ed Cole transferred from Cadillac to Chevrolet, he soon dismissed the original design and challenged his engineers to develop a more compact design that would be easier to manufacture. Cole had previously worked in engineering, rising to co-head a team that had developed the 1949 Cadillac V8.
The legacyof Chevrolet small-blocks began with the 1955 Chevrolet 265-cubic inch displacement (cid) V8 offered in the Corvette and Bel Air. It quickly gained popularity among stock car racers, for its light weight and durability. Full flow oil filtration was introduced in 1956. The following year, the small block grew to 283-cid, eventually becoming a stalwart of the GM engine line.
History was in the making, because when equipped with an optional Rochester fuel injection system, it became one of the first production engines ever to make one horsepower per cid. The high-performance 327-cid version followed, delivering as much as 375 hp and increasing the horsepower to displacement ratio even more. These important benchmarks set consumer expectations as the industry continued its unrestrained development.
For most people, it was the 350-cid engines that became best known as the Chevrolet small block. The engine’s oversquare 4.00-inch bore and 3.48-inch stroke are virtually identical to the modern, 400+ hp LS3 engine. Some engine design fundamentals do not change over time.
Cole ordered engine compression ratios reduced after 1970 knowing that EPA regulations would tighten. Among many other things, he can be credited with getting American cars away leaded gasoline and preparing for the arrival of catalytic converters. It would take another 28 years before all Gen I engines were no longer used in production. From 1997 to 2003, they were known as Vortec truck engines.
The LT1 small block engine broke cover in 1992. The mechanical simplicity and established reliability of the pushrod-driven, 2-valve design was augmented by a reverse flow cooling system. The 5.7-liter V8 cooled the cylinder heads first, then the engine block. This provided lower cylinder temperatures, which opened up the use of higher compression ratios than could be handled with the previous generation.
Additional improvements, including a low-profile, high-flow intake manifold, previewed technology that would be carried forward into future designs. There were several variants on the basic LT1 design. Cast iron blocks, fitted with aluminum heads would find their way into the Y and F bodies. All cast iron versions populated the B and D body lines. Blocks for the Corvette were updated to have four-bolt main bearing caps, while most other blocks used two-bolt mains.
In 1996, a special version was built for the last year of the C4 Corvette. Using a port-matched intake, high flow cylinder heads, valvetrain and camshaft revisions, the LT4 engine delivered 330 hp and 340 ft-lb. of torque. The lT4 would see additional duty the following year in special models of the F-body cars.
Earlier, Chevrolet had released the Corvette ZR-1 with the radical overhead cam engine, designated the LT5. This all-aluminum 5.7 L small-block V8, was thoroughly different from any of the other Chevrolet 350 engines, sharing only the 4.4-inch bore spacing.
The bore and stroke were both different and it used Lotus-designed 32-valve DOHC cylinder heads. Due to its expensive nature, GM canceled the ZR-1 option after six years of production. The LT5 led to a new class of premium V8s, however. The DOHC Northstar V8 and its derivatives, drew heavily from the design and lessons learned from LT5 production.
Gen III was introduced as the LS1 5.7-liter engine in the 1997 Corvette, while Vortec versions for trucks appeared in 1999, with displacements ranging from 4.8 liters to 6.0 liters.
Gen II-LT engines disappeared in 1997, while Gen I was completely displaced by 2000. Like the previous two generations, these engines would find widespread application across all GM brands. Aluminium blocks were used for cars and iron for most truck applications. Exceptions include the TrailBlazer SS, the SSR and some Z71 pickup trucks.
The architecture of the LS series made for an extremely strong engine block. The aluminium engines being nearly as strong as previous generation iron block engines. The iron LS engines far exceeded any capabilities of the previous two generations. This version also debuted coil-on-plug ignition, along with a firing order change to 1-8-7-2-6-5-4-3. The LS series was now consistent with the firing pattern of other modern V8 engines.
The Gen III engine benefited from significant new technology, including replicated cylinder head ports, six-bolt mains, gerotor oil pump and composite intake manifold, but its design drew upon more than 40 years of research and continuous improvement from the Gen I and Gen II small-blocks.
In 2005, the Generation IV engines emerged, with provisions for high-displacement ranges (up to 7011 cc, or 427.8 cu in) and power output as high as 638 hp. The new architecture was designed with displacement on demand in mind, a technology that allows 4 cylinders in alternating fashion from side to side and front to back to be deactivated. It can also accommodate variable valve timing, which improves torque, fuel economy and emissions. Fuel economy improvements as high as 12% have been obtained because of this.
The current fourth-generation small block engine powers the Chevrolet Corvette, Cadillac CTS-V as well as many other models. Many Gen IV variants can run on gasoline, E85 ethanol or any combination of the two.
The LS2 saw duty as the Corvette’s new base engine for the 2005 model year, as well as becoming the standard powerplant for the 2005-2006 GTO. It produces 400 bhp from a slightly larger displacement of 5,967 cc (5.967 L; 364.1 cu in). Similar to the Generation III LS6, the LS2 shows improved torque throughout the rpm range.
Modern challenges will continue to require evolution of the GM small block. The coming use of gasoline direct injection will necessitate a significant redesign of the cylinder heads and the higher output may demand a more robust, but lighter block. The newly mandated Corporate Average Fuel Economy requirements may not kill off the small block V8 engine, but could drive it back to its roots, at least in terms of displacement.
Small Block Milestones
The legacy of the General Motors small-block has left an indelible mark on the global auto industry and American automotive culture. Some of its many noteworthy milestones include:
- 1955: Small-block V-8 introduced in 1955 Chevrolets.
- 1957: Larger bore increased displacement to 283 cubic inches; Ramjet mechanical fuel injection was introduced, bringing horsepower to 283 – one horsepower for every cubic inch.
- 1962: Displacement increased to 327 cubic inches, with Ramjet fuel injected version rated at 360 horsepower.
- 1964: Cylinder head improvements bump the 327’s highest horsepower rating to 375 with fuel injection.
- 1967: Little-known option Z28 released for the Camaro, which includes a high-revving 302-cubic-inch small-block for competition in SCCA Trans Am road racing
- 1968: A Camaro Z28 wins the Trans Am championship; a 350-cubic-inch (5.7 liters) version of the small-block debuts and would become the quintessential small-block variant.
- 1970: 350-cubic-inch LT1 debuts in Camaro and Corvette and is rated at 370 horsepower; 400-cubic-inch small-block is offered – the largest-displacement small-block built.
- 1975: With fuel economy prevalent in consumers’ minds, a more efficient 262-cubic-inch small-block is introduced.
- 1978: V-6 engine based on small-block design introduced; it would become the Vortec V-6 truck engine more than a decade later.
- 1980: Last year for the 400 small block.
- 1982: Fuel injection reintroduced with the Cross-Fire injection system on Corvette and the redesigned Camaro Z28.
- 1985: Tuned port fuel injection replaces Cross-Fire Injection, ushering in the modern era of electronically controlled, port-injected engines.
- 1986: Aluminum cylinder heads debut as standard equipment on Corvette; block changed to accept new single-piece rear main seal.
- 1987: Hydraulic roller lifters introduced.
- 1989: The H.O. 350 “crate engine” is developed, offering a ready-built performance engine from the factory. It would change the way hot rodders approach engine building in the next decade.
- 1992: LT1 engine in the Corvette introduces Gen II small block design, which features reverse-flow cooling, revised cylinder head design, and crank-triggered optical distributor.
- 1996: Vortec V-8 engines introduced in trucks, featuring cylinder heads with swirl-inducing combustion chamber design to increase power and torque.
- 1997: Gen III 5.7-liter LS1 small-block introduced with all-new Corvette, featuring all-new deep-skirt block casting with six-bolt mains; redesigned cylinder heads with symmetrical ports and combustion chambers; and coil-near-plug ignition system.
- 1999: Gen III-based Vortec V-8 engines introduced in GM trucks; displacements include 4.8 liters, 5.3 liters and 6.0 liters.
- 2005: Gen IV small-block introduced 50 years after the original.