Introduction

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 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Finally superseded by GM's Generation II LT and Generation III LS V8s in the early 2000s and discontinued in 2004, the engine is still made by a GM subsidiary in Mexico as an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.

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. It did not have a provision for an oil filter. The familiar oil filter boss on the small block came around in 1956, along with an all new casting. 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.

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 ever to make one horsepower per cubic inch. Chevrolet went to an new motor mounting system placing the mounts near the freeze plugs on the side of the block. The old system had mounts located on the front of the block at either side of the timing cover. The 283 would later be extended to other Chevrolet models, replacing the old style 265 V8s.

The 327 cu in (5.4 L) debuted in 1962, turning out as much as 375 hp and increasing horsepower per cubic inch to 1.15. Fitted with its own unique valve cover that featured a flat spot for a decal like "327 Turbo Fire". This design was used until around 1965 and is very popular with collectors today. The 1956-1967, small block Chevys also used a cartridge type oil filter inside a steel canister. In 1968 the small block had a spin on style oil filter. There are adapters available to update the older style blocks to the newer style.

Before 1963, the small block Chevy engine used a "Road Draft Tube" to ventilate the crankcase. Featuring a large hole at the top rear of the block inside the lifter valley. These blocks are from the 1950's through to the mid 1960's. The PCV (positive crankcase ventilation system) replaced the daft tube in 1963. The vent hole disappeared in 1968 when the system was redesigned to ventilate through the oil filler tube located at the front of the intake manifold. Later engines ventilated through the valve cover.

Since around 1964 most small block Chevys have had two threaded holes at the rear of the block on the drivers side near the oil filter boss. These are to accomodate the clutch counter shaft for vehicles with manual transmissions. Only one of the holes are required. Some vehicles used a counter shaft located approx 6" further to the rear, thus the need for the rear hole. Early blocks have only one hole and are pretty much worthless to a vehicle that requires the rear hole for their clutch assemblies.

In 1962 Chevy came out with the Chevy II, or Chevy Deuce. Using an inverted front suspension, the Chevy II had shock towers in the engine bay. This put the steering arms right where an V-8, oil pan would go. This problem was solved for the small block applications with a special block with a recessed oil filter boss and an oil dipstick located on the passenger side. The problem was done away with in 1968 with a new chassis and body style. The unique 64-67 blocks are in demand by collectors due to the recessed oil filter boss.

Several changes took place to the small block Chevy in 1967. It was the last year of the 283 CID and the first year of the 350 CID (Camaro only).It was also the first of three years for the famous 302 CID (283 crank in a 327 block).

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.

1968 was the year that Chevy started making the small blocks with large journal cranks, that greatly improved the strength and durability to the crank. This also means that small journal(pre 1968) cranks do not fit large jounal blocks (post 1968). Although this change did not occur until around March or April of 1968. 1968 marked the first year of the 307 CID. The 307 CID utilized the stroke of a 327 CID and the bore of a 283 CID. Chevy tried again with an economy small block with the 305 that is now not considered a performance engine.

1969 brought with it 4 bolt main bearing caps that further strengthened the bottom end of the small block for high performance and heavy duty applications. 1969 also marked the last year on the 327 CID as well as the 302 CID.

The Chevy small block grew to it's largest factory displacement of 400 CID in 1970. This block required siamesed cylinders to gain the internal space for the displacement. Extra holes were also drilled into the surface of each deck to promote cooling. Therefore with the use of a small block 400 CID, you also need the small block 400 heads. Many of the crankshafts and connecting rods from the small block 400's ended up with a better life as part of a 383 build-up. These engines are referred to as Stroker 383 engines.

Another year of change was 1986. The two piece rear main seal was replaced with a one piece unit. Displacement of the block was also cast into the block next to the casting number.

Though not offered in GM vehicles since 2004, the Gen I small block 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.