The Chevrolet small-block engine is a series of automobile V8 engines built by the Chevrolet Division of General Motors using the same basic small (for a V8) engine block. Retroactively referred to as the "Generation I" small-block, it is distinct from subsequent "Generation II" LT and "Generation III" LS engines.Production of the original small-block began in 1955 with a displacement of 265 cu in (4.3 L), growing incrementally over time until reaching 400 cu in (6.6 L) in 1970. Several intermediate displacements appeared over the years, such as the 283 cu in (4.6 L) that was available with mechanical fuel injection, the 327 cu in (5.4 L) (5.3L), as well as the numerous 350 cu in (5.7 L) 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 four of Chevrolet's siblings of the period (Buick, Cadillac, Oldsmobile, and Pontiac) designed their own V8s, it was the Chevrolet 350 cu in (5.7 L) small-block that became the GM corporate standard. Over the years, every American General Motors division except Saturn used it and its descendants in their vehicles.Finally superseded by GM's Generation II LT and Generation III LS V8s in the 1990s and discontinued in 2003, the engine is still made by a GM subsidiary in Mexico as an aftermarket replacement. In all, over 90,000,000 small-blocks have been built in carbureted and fuel injected forms since 1955.The small-block family line was honored as one of the 10 Best Engines of the 20th Century by automotive magazine Ward's AutoWorld. The Chevrolet 90-Degree V6 engine, which is still in production, is this original small-block (and NOT the newer LS1) but minus cylinders #3 and #6
Confusion with LT and LS engines
The original Chevrolet-designed small-block is a specific family of engines manufactured originally in 1955 and installed as production powerplants by GM for 48 years.Subsequent GM small block V-8 engine designs built on different blocks are often confused with the original small-block. For more information on the Generation II small-block V8s, which differ mainly in their reverse-flow cooling system, see the GM LT engine. For more information on the current family of Chevy Generation III/IV General Motors small-block V8s see the GM LS engine.
Overview
The first generation of Chevrolet small-blocks began with the 1955 Chevrolet 265 cu in (4.3 L) V8 offered in the Corvette and Bel Air. Soon after being introduced, it quickly gained popularity among stock car racers, becoming known as the "Mighty Mouse" motor, after the popular cartoon character of the time, with the simpler "Mouse" nickname becoming much more popular as time went on.By 1957 it had grown to 283 cu in (4.6 L). Fitted with the optional Rochester mechanical fuel injection, it became one of the first production engines to make one horsepower per cubic inch. The 283 would later be extended to other Chevrolet models, replacing the old style 265 V8s.
A high-performance 327 cu in (5.4 L) variant followed, turning out as much as 375 hp and increasing horsepower per cubic inch to 1.15.
It was, however, the 350 cu in (5.7 L) series that came to be the best known Chevrolet small block. The engine's oversquare 4.00-inch bore and 3.48-inch stroke (102 mm by 88 mm) are nearly identical to the 436 hp (325 kW) LS3 engine of today, but much has changed. Installed in everything from station wagons to sports cars, in commercial vehicles, and even in boats and (in highly modified form) airplanes, it is by far the most widely used small-block of all-time.
Though not offered in GM vehicles since 2004, the 350 cu in (5.7 L) series is still in production today at General Motors' Toluca, Mexico plant under the company's "Mr Goodwrench" brand, and is also manufactured as an industrial and marine engine by GM Powertrain under the Vortec name.
From 1955–74, the small-block engine was known as the "Turbo-Fire V8".
Small Block Chevrolet V8 (1955–1998)
The small-block made its debut in 1955 and remained popular for over five decades for its relatively compact size, light weight, and extensive aftermarket support. The engines have been placed into families with the name of each family being the bore size of that family’s progenitor.
3.750/3.875 in. bore family (1955–1973)
All Chevy V8s, from the big blocks to today's LS7 and LS9, evolved from the 265/283 small block family. Of the three engines in this family, two of them, the 265 and the 283, have gone down in automotive history. The first of this family was the 265, introduced in 1955. The 283, famous for being one of the first engines to make 1 hp per cubic inch, is also famous for being the evolutionary stepping stone that would later give rise to small blocks and to the “W” blocks, ultimately culminating in the Chevy big blocks. The last of this family was the 307, which was a stroked 283 with a medium journal.
265
The 265 cu in (4.3 L) V8 was the first Chevrolet small block. Designed by Ed Cole's group at Chevrolet to provide a more powerful engine for the 1955 Corvette than the model's original "stove bolt" in-line six, the 165 hp (123 kW)[2] 2-barrel debut version went from drawings to production in just 15 weeks.
A pushrod cast-iron engine with hydraulic lifters, the small block was available with an optional 4-barrel Rochester carburetor, increasing engine output to 195 hp (145 kW). The oversquare (3.75 in (95 mm) bore, 3 in (76 mm) stroke) engine's 4.4 in (111.8 mm) bore spacing would continue in use for decades.
Also available in the Bel Air sedan, the basic passenger car version produced 162 hp (121 kW) with a 2-barrel carburetor. Upgraded to a four-barrel Rochester, dual exhaust "Power Pack" version, the engine was conservatively rated at 180 hp (134 kW).
A shortcoming of the 1955 265 was that the engine had no provision for oil filtration built into the block, instead relying on an add-on filter mounted on the thermostat housing. In spite of its novel green sand foundry construction, the '55 block's lack of adequate oil filtration leaves it typically only desirable to period collectors.
The 1956 Corvette introduced three versions of this engine – 210 hp (157 kW) with a single 4-barrel carb, 225 hp (168 kW) with twin 4-barrels, and 240 hp (179 kW) with twin fours and a high-lift cam.
283
The 265 ci V-8 was bored out to 3.875 in (98.4 mm) in 1957, giving it a 283 cu in (4,638 cc) displacement. The first 283 motors used the stock 265 blocks. However, the overbore to these blocks resulted in thin cylinder walls. Future 283 blocks were recast to accept the 3.875 bore. Five different versions between 185 hp (138 kW) and 283 hp (211 kW) were available, depending on whether a single carb, twin carbs, or fuel injection was used. Fuel injection yielded the most power. Horse power was up a bit each year for 1958, 1959, and 1960. The 1957 Ramjet mechanical fuel injection version produced an even 1 hp per cubic inch (61 hp/L), an impressive feat at the time. Many thought this as the first US-built production V8 to produce one horsepower per cubic inch. However, it was preceded in this achievement by Chrysler in 1956.Besides being available in the Chevrolet line, it was optional in Checker Taxis beginning in 1965.[3] A version of it that was built by GM Canada was also available in Studebakers produced in Canada for 1965 & 1966.
307
A 307 cu in (5,025 cc) version was produced from 1968 through 1973. Engine bore was 3.875 inches (98.4 mm) with a 3.25-inch (82.6 mm) stroke.
4.00 in bore family (1962–1998)
Originally intended as the performance block, this engine family through the 350 CID became an all purpose engine that saw use in many applications from Corvettes to vans. All engines in this family share the same block dimensions and sometimes even the same casting number; the latter meaning engines were of the same block, but with different strokes (e.g. the casting number 3970010 was used by all three engines: 302, 327, and 350). This engine family was updated in 1968 for the use of 2.45” medium-sized journals. The first engine in this family was the small journal 327 in 1962 and the last being 1992's medium journal 350. The medium journal 350 would later be further developed into the "Generation II" LT 350 in the early 1990s.
302
Chevrolet produced a special 302 cu in (4.9 L) (referred to as 5.0 L) engine for Sports Car Club of America SCCA Trans-Am Series racing from 1967–1969. It was the product of placing the 283 3-inch stroke crankshaft into a 4-inch bore 327 block. The 1967 302 used the same nodular cast-iron crank as the 283[4], with a forged-steel crankshaft that was also produced. This block is one of 3 displacements, 302/327/350, that underwent a crankshaft bearing diameter transformation for 1968 when the rod-journal size was increased from the 2.00 in. diameter small-journal to a 2.10 large-journal and the main-journal size was increased from 2.30 in. to 2.45. The large-journal connecting rods were heavier and used 3/8 in. 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 heavier 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 8.00 in. diameter harmonic balancer. This engine was used only in the first-generation (1967-69) Z/28 Camaro. It had a 3/4-length semi-circular windage tray, heat-treated, magnafluxed, and shot-peened forged 1038-steel 'pink' connecting rods, floating-pin in `69, and forged-aluminum pistons with higher scuff-resistance, better sealing single-moly rings. Its solid-lifter cam, known as the '30-30 Duntov' cam named after its .030/.030 in. intake/exhaust hot valve-lash and Zora Arkus-Duntov (the Duntov cam was the .012/.018 1957 camshaft known as the '097', which referred to the last three digits of the casting number) the "father of the Corvette", was also used in the 1964-65 carbureted 327/365 and F.I. 327/375 engines. It used the '202' 2.02/1.60 valve diameter high-performance 327 double-hump #461 heads, 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 runners and smoother passage turns was introduced for the Z/28 that the LT-1 350 1969 Corvette and 1970 Z/28 were equipped with until 1973. Unlike the Corvette, the exhaust manifolds were the more restrictive rear outlet 'log' design to clear the Camaro's front cross-member. It had a chrome oil filler tube and valve covers from 1967 to 1968, and chrome 14.00 x 3.00 in. drop-base open-element air-cleaner assembly on a 780cfm vacuum secondary Holley 4-Bbl carburetor. A 'divorced' exhaust crossover port heated well-choke thermostat coil was used to provide cleaner and faster engine warm-up. Its single-point distributor had an ignition point cam designed to reduce point-bounce at high-rpm along with a vacuum diaphragm to advance ignition timing at idle and part-throttle for economy and emissions. Balancer and water-pump pulleys, as well as optional power-steering pullies, were deep-groove for fan belt retention at high-rpm. In 1969, the 302 shared the finned cast-aluminum valve covers with the LT-1 350 Corvette engine. Conservatively rated at 290 hp (216 kW) (SAE gross) at 5800 rpm and 290 lb-ft at 4800, actual output with its production 11:1 compression ratio was around 376 hp (280 kW) with 1.625 in. primary x 3.0 secondary tubular headers that came in the trunk when ordered with a new Z/28, carburetor main-jet, and ignition timing tuning.
After the 1967 Trans-Am campaign with the 4-Bbl induction system producing more horsepower than the competing auto makers' 8-Bbl systems, for 1968 Chevrolet developed a factory 'cross-ram' aluminum intake-manifold package using two Holley 585cfm 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' off-road cam, the package increased a stock 302's hp from 360 hp to approximately 400. Chevrolet went so far as to carry the positive crankcase ventilation (PCV) 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 465 hp with little more than the 8-Bbl induction, ported heads with higher pressure valvesprings, roller rocker arms, and the '754' 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. In 1969, factory ZL-2 cowl-induction hoods were available for both the single and dual four-barrel induction systems that were sealed to the air-cleaner base ensuring cooler, high-pressure, dense air from the center of the base of the windshield was supplied to the engine for combustion smoothness and maximum power production. Another popular service-parts-only component used on the 302 was the Delco transistor-ignition distributor, introduced in 1967 and also used in the L88 427 Corvette, that eliminated the production breaker-point ignition allowing more stable ignition-timing at high engine speeds.The 302's bore/stroke and rod/stroke geometries made it a natural high-rpm 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, the pinnacle of the 302's use in professional racing was its being the primary engine that powered the outstanding but overshadowed 1968-1976 SCCA Formula 5000 Championship Series, a SCCA Formula A open-wheel class designed for lower cost. Weighing 1400 lbs., with 525-550 hp, a 5-spd. magnesium transaxle, and 20 in. wide 15 in. rear wheels, it produced incredibly exciting racing. Prepared with a Lucas-McKay mechanically-timed fuel-injection individual-stack magnesium induction-system that was paired with ported production double-hump iron heads and a virtually stock production crankshaft, it had a lasting impact on the series' ability to conduct high car-number finishes and close competition events by the degree of mechanical success it provided to a series filled with star international Grand Prix drivers like David Hobbs, Brian Redman, Jody Scheckter, and Mario Andretti.
