Chevrolet small-block engine (first- and second-generation)


The Chevrolet small-block engine is a series of gasoline-powered V8 automobile engines, produced by the Chevrolet division of General Motors in two overlapping generations between 1954 and 2003, using the same basic engine block. Referred to as a "small-block" for its size relative to the physically much larger Chevrolet big-block engines, the small-block family spanned from to in displacement. Engineer Ed Cole is credited with leading the design for this engine. The engine block and cylinder heads were cast at Saginaw Metal Casting Operations in Saginaw, Michigan.
The [|Generation II] small-block engine, introduced in 1992 as the LT1 and produced through 1997, is largely an improved version of the Generation I, having many interchangeable parts and dimensions. Later generation GM engines, which began with the Generation III LS1 in 1997, have only the rod bearings, transmission-to-block bolt pattern and bore spacing in common with the Generation I Chevrolet and Generation II GM engines.
Production of the original small-block began in late 1954 for the 1955 model year, with a displacement of, growing over time to by 1970. Among the intermediate displacements were the,, and numerous versions. Introduced as a performance engine in 1967, the 350 went on to be employed in both high- and low-output variants across the entire Chevrolet product line.
Although all of Chevrolet's siblings of the period designed their own V8s, it was the Chevrolet small-block that became the GM corporate standard. Over the years, every GM division in America, except Saturn and Geo, used it and its descendants in their vehicles. Chevrolet also produced a big-block V8 starting in 1958 and still in production as of 2024.
Finally superseded by the GM Generation III LS in 1997 and discontinued in 2003, the engine is still made by a General Motors subsidiary in Springfield, Missouri, as a crate engine for replacement and hot rodding purposes. In all, over 100,000,000 small-blocks had been built in carbureted and fuel injected forms between 1955 and November 29, 2011. The small-block family line was honored as one of the 10 Best Engines of the 20th Century by automotive magazine Ward's AutoWorld.
In February 2008, a Wisconsin businessman reported that his 1991 Chevrolet C1500 pickup had logged over one million miles without any major repairs to its small-block V8 engine.
All first- and second-generation Chevrolet small-block V8 engines share the same firing order of 1-8-4-3-6-5-7-2.

Overview

The first generation of Chevrolet small-blocks began with the 1955 Chevrolet 265 cu in V8 offered in the Corvette and Bel Air. The engine quickly gained popularity among stock car racers, and was nicknamed the "Mighty Mouse," after the then-popular cartoon character, later abbreviated to "Mouse". By 1957 the engine had grown to. Fitted with the optional Rochester mechanical fuel injection and a Duntov high-lift camshaft, it was one of the first production engines to produce per. The 283 was adopted by other Chevrolet models, replacing the 265 V8s.
A high-performance variant followed, turning out as much as and raising horsepower per cubic inch to. From 1954 to 1974, the small-block engine was known as the "Turbo-Fire" or "High Torque" V8. However, it was the series that became the best-known Chevrolet small-block.
Installed in everything from station wagons and sports cars to commercial vehicles, boats, industrial equipment, and even in aircraft, the 350 is the most widely used small-block engine of all time. Though not offered in GM vehicles since 2003, the 350 series is still in production at a GM subsidiary in Springfield, Missouri, under the company's "GM Genuine Parts" brand, and is also manufactured as an industrial and marine engine by GM Powertrain under the "Vortec" name.

3.750 in. bore family (1955–1957)

265

The "Turbo-Fire" V8 was the second Chevrolet small-block; the first Chevrolet V8 was produced in 1917. The 265 cu in Turbo Fire engine was designed by Ed Cole's group at Chevrolet to provide a more powerful engine for the 1955 Corvette than the model's original "Blue Flame" in-line six; the 2-barrel debut version went from drawings to production in just 15 weeks.
Cole's design borrowed a stud-mounted independent ball rocker arm valvetrain design patented by Pontiac engineer Clayton Leach scheduled to be used in the 1955 Pontiac V8. Internal GM rules at the time held that an automotive division developing a technological innovation had the right to introduce it and enjoy a two-year hiatus before any other GM division could share it. GM overruled itself and both divisions debuted the new design. This provided a considerable advantage to Chevrolet, as the Pontiac V8's introduction had been held back: it had been tracking for introduction in the 1953 model year, and all 1953 and 1954 Pontiac cars' chassis and suspensions had been designed for the new engine. But GM's Buick division had successfully lobbied corporate management to postpone Pontiac's engine until late 1954 in favor of Buick's release of its new overhead valve V8 engine in 1953.
An OHV engine with hydraulic lifters, the small-block was available with an optional four-barrel Rochester carburetor, increasing engine output to, or in the Corvette. The short-stroke bore × stroke engine's bore spacing would continue in use for decades.
Also available in the Bel Air sedan, the basic passenger car version produced with a two-barrel carburetor. Upgraded to a four-barrel Rochester, dual exhaust "Power Pack" version, the engine was conservatively rated at, and with the "Super Power Pack," it was boosted up to the power level of the Corvette.
A shortcoming of the 1955 265 was its lack of any provision for oil filtration built into the block, instead relying on an add-on filter mounted on the thermostat housing, and that was an "option only." In spite of its novel green sand foundry construction, the lack of adequate oil filtration leaves it typically only desirable to period collectors.
The 1956 Corvette introduced three versions of this engine— with a single 4-barrel carburetor, with twin 4-barrels, and with two four-barrel carburetors and a high-lift camshaft.

Output

3.875 in. bore family (1957–1973)

283

The engine appeared in 1957, achieved by boring out the by, yielding a bore × stroke. The first 283 motors used the stock 265 blocks. However, the overbore resulted in thin cylinder walls, causing future 283 blocks to be cast to accept the larger bore. Multiple different versions between and were available, variously with a single carburetor, twin carburetor, or fuel injection.
Horsepower was up a bit each year from 1958 to 1961. The 1957 Rochester Ramjet mechanical fuel injection version produced an even 1 hp per cu in, an impressive feat at the time. This was the third U.S.-built production V8 to produce one horsepower per cubic inch, after the 1956 Chrysler 300B and DeSoto Adventurer.
The 283 engine was optional in Checker Taxis beginning in 1965. A GM Canada version was also available in Studebaker vehicles produced there for 1965 and 1966.

Output

307

An economy version was produced from 1968 through 1973 as Chevrolet adjusted to increasingly stringent federal emissions standards. Engine bore and stroke was. All 307s had two-barrel carburetors, and large journals to accept the 327's crankshaft. Pistons used with the 307 share the same pin height as the 327 but retain the 283's bore size.
Originally intended as the Chevrolet Division's performance block, the 4.000 in bore engine family was introduced in a displacement in the 1962 Corvette. This was followed by a de-stroked racing version introduced in the 1967 Chevrolet Camaro Z/28. The first displacement was the high-performance L-48 option for the 1967 Camaro. Many variants of 350 followed, at all levels of performance, turning it into an all-purpose engine that saw use in applications from Corvettes to trucks. All engines in this family share the same block dimensions and sometimes even the same casting number; the latter indicating engines were of the same block, but with different strokes.
The engine family received a increase in main journal size in 1968 to. The last variant a 2000s 350 used in pickup trucks and commercial vehicles.
The medium journal 350 was further developed into the Generation engine GM LT engine 350 in the early 1990s.

302

In 1966, General Motors designed a special engine for the production Z/28 Camaro in order for it to meet the Sports Car Club of America Trans-Am Series road racing rules limiting engine displacement to from 1967 to 1969. It downsized the standard Chevrolet V8 by swapping out its crankshaft for a special forged steel high-performance version of the shorter throw crank from the engine, decreasing stroke length while holding cylinder bore the same. The result was a highly oversquare bore × stroke, well-suited to fast-revving racing applications.
Every part in a SCCA Trans-Am engine had to be available through local Chevrolet parts departments to comply with race homologation regulations.
The 302 engine also joined the 327 and 350 in getting larger crankshaft bearings in 1968, with the rod-journal diameter increased from the small-journal to a large-journal, and a main-journal increase from to a medium-sized.
The large-journal connecting rods were thicker and used diameter cap-bolts to replace the small-journal's 11/32. 1968 blocks were made in 2-bolt and 4-bolt versions with the 4-bolt center-three main caps each fastened by two additional bolts which were supported by the addition of thicker crankcase main-web bulkheads. When the journal size increased to the standard large-journal size, the crankshaft for the 302 was specially built of tufftride-hardened forged 1053-steel and fitted with a high-rpm diameter harmonic balancer. It had a -length semi-circular windage tray, heat-treated, magnafluxed, shot-peened forged 1038-steel 'pink' connecting rods, floating-pin in 1969, forged-aluminum pistons with higher scuff-resistance and better sealing single-molybdenum rings.
Its solid-lifter cam, known as the "30-30 Duntov", named after its /0.030 in hot intake/exhaust valve-lash and Zora Arkus-Duntov, the "Father of the Corvette", was also used in the 1964–1965 carbureted 327 cu in/365 gross hp and fuel injected 327/375 engines. It used the '202' / valve diameter high-performance 327 double-hump 186 and 461 heads, pushrod guide plates, hardened 'blue-stripe' pushrods, edge-orifice lifters to keep more valvetrain oil in the crankcase for high-rpm lubrication, and stiffer valvesprings. In 1967, a new design high-rise cast-aluminum dual-plane intake manifold with larger smoother turn runners was introduced for the Z/28 that the /370 gross hp 1970 LT-1 also used.
Unlike the Corvette, the exhaust manifolds were the more restrictive rear outlet 'log' design to clear the Camaro chassis's front cross-member. It had a chrome oil filler tube in the front of the intake manifold next to the thermostat housing from 1967 to 1968. The first year had unique chrome valve covers with Chevrolet stamped into them without an engine displacement decal pad. In 1968, the engine had the chrome covers, but without the Chevrolet name, connected to a PCV valve and a chrome drop-base open-element air cleaner assembly fitted with a crankcase breather on a vacuum secondary Holley 4-Bbl carburetor. 1969 Corvette and 1970 Z/28 engines were also equipped with this Holley carburetor until the Quadrajet carburetor returned in 1973. A 'divorced' exhaust crossover port heated well-choke thermostat coil was used to provide cleaner and faster engine warm-up. Its cast-aluminum distributor had a vacuum diaphragm to advance ignition timing at part-throttle for economy and emissions, and came in single-point in the Camaro, with an ignition point cam designed to reduce point bounce at high rpm, and transistorized in the Corvette.
Pulleys for the balancer, alternator, water-pump, as well as optional power steering, were deep-groove to retain the drive belts at high rpm. In 1969, the 302 shared the finned cast aluminium valve covers with the LT1 350 Corvette engine. Conservatively rated at at 5800 rpm and at 4800, actual output with its production 11.0:1 compression ratio was around with primary x collector Sanderson tubular headers that came in the trunk when ordered with a 1967 Z/28, and associated carburetor main jet and ignition timing tuning. In 1968, the last year for factory headers, they had primaries x collectors. A stock 1968 Z/28 with the close-ratio transmission, optional transistorized-ignition, and 4.88 gear, fitted with little more than the factory cowl plenum cold-air hood induction and headers, was capable of running 12.9 second/ Dragstrip| times on street tires.
After the 1967 Trans-Am campaign with the four-barrel induction system producing more horsepower than the competing automakers' eight-barrel systems, Chevrolet developed a factory 'cross-ram' aluminum intake-manifold package for 1968 using two Holley mechanical secondary carburetors for Trans-Am racing. It was available only as off-road service parts purchased over the Chevrolet dealership parts counter. With the Chevrolet 140 1st-design off-road cam, the package increased a stock 302's horsepower from to approximately. Chevrolet carried the positive crankcase ventilation system over to the cross-ram induction system to retain emissions compliance mandated for U.S.-produced cars beginning in 1967, that also provided full-throttle crankcase pressure venting to the intake air to burn its vapors.
Engines prepared for competition use were capable of producing with little more than the paired 4-barrel carburators, ported heads with heavy duty valve springs, roller rocker arms, and the 754 2nd-design road-race cam. 1967–1968 models' cowl-induction system had an enclosed air-cleaner assembly ducted from its passenger side into the firewall cowl above the heater core.
Another popular service-parts-only component used on the 302 was the magnetic-pulse Delco transistor-ignition ball bearing distributor. Introduced in 1963 on Pontiac's drag racing engines, General Motors fitted it to the 1967 Z/28 before they used it on the L88 Corvette. It eliminated the production breaker-point ignition, allowing greater spark energy and more stable ignition timing at all engine speeds, including idle. This was one of the least talked about yet most transformative and comprehensive performance and durability upgrades of its time. Many of the 302s off-road service parts were the development work of racers like Roger Penske.
While the 302 became a strong Limited Sportsman oval track racing engine in the hands of racers like Bud Lunsford in his 1966 Chevy II, its bore/stroke and rod/stroke geometries made it a natural high-rpm road-racing engine and were responsible for its being among the more reliable production street engines homologated for full competition across all the American makes, winning back-to-back Trans-Am Championships at the hands of Mark Donohue in 1968 and 1969. However, with engines built by Al Bartz, Falconer & Dunn and Traco Engineering, the pinnacle of the 302's use in professional racing, was its being the primary engine that powered the outstanding but overshadowed 1968–1976 Formula 5000 Championship Series, a SCCA Formula A open-wheel class designed for lower cost. They were also used in period endurance racing, such Traco-engined Lola T70's in the 24 Hours of Daytona and the 12 Hours of Sebring.
The engine was also popular in Formula 5000 racing around the world, especially in Australia and New Zealand where it proved more powerful than the Repco-Holden V8. Weighing, with a iron block and head engine positioned near the car's polar moment of inertia for responsive turn pivoting, a Hewland 5-speed magnesium transaxle, and wide front/ wide rear magnesium wheels, it produced incredibly exciting racing. They ran in 2.8 seconds and over.
Reminiscing about the series, mid-70s Australian F5000 driver Bruce Allison said, "We never used first gear at the start. We started in second, and even then there was so much torque, you'd get wheelspin through third and fourth gears." Prepared with a Lucas-McKay mechanically timed individual-stack magnesium fuel-injection induction system that was paired with ported production car double-hump iron heads, a rev-kit fitted roller lifter camshaft, roller bearing rocker arms, and a virtually stock production crankshaft, it had a lasting impact on the series' ability to conduct high car-count finishes and close competition events by the degree of mechanical success it provided to a series filled with star international Grand Prix drivers like Mario Andretti, Mark Donohue, David Hobbs, Graham McRae, Brian Redman, Jody Scheckter, and Al and Bobby Unser.