Small block V8: 262, 265, 267, 283, 302, 305, 307, 327, 350, 400

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As you are probably aware the release of the 265 cid engine in 1955 introduced a revolutionary engine design that has become one of the most, if not the most, popular overhead valve V8 engines ever manufactured. Often referred to as a "small block" or "mouse motor" due to its design and not necessarily its cubic-inch displacement possibilities. The 348 cid and 409 cid engines used from 1958 through early 1965 essentially truck engines and are often referred to as "w-engines" due to their unique cylinder head configuration. When General Motors introduced the Mark-IV 396 engine in mid- 1965 it was referred to as a "big block" or "rat motor."

The venerable small block engine has ranged in cubic-inch size from 262 to 400 in factory form until its demise in 2003, an impressive 48 year run, in favor of a new generation of small block V8s. Factory horsepower ratings ranged from 110 horsepower with the 262 V8 engine to a whopping 370 horsepower with the LT1 Corvette in 1970 before horsepower ratings were drastically cut in 1971 due to government emissions requirements.

Fuel systems included 2-barrel carburetor versions, 4-barrel carburetor versions, 2x4-barrel carburetor versions, and fuel injection.

Probably no small block cylinder head is more misunderstood than the infamous "camel hump," or "double hump" cylinder heads. Three castings used this symbol from 1962 through 1968. Casting numbers  3774682, 3782461, and 3917291 have this casting symbol and were used on both standard and high performance engines. The major difference in the heads is the intake and exhaust valve sizes. Standard cylinder heads have1.94" intake valves and 1.50" exhaust valves where the high performance cylinder heads have 2.02" intake valves and 1.60" exhaust valves. There are as differences in the combustion chamber volume that are too extensive to mention here. So, when someone touts "camel hump" heads it DOES NOT ALWAYS mean high performance. Low performance cylinder heads used a press fit rocker arm stand as opposed to screw-in rocker arm stand for high performance durability.

Beginning in sometime 1968, Chevrolet moved the water temperature sending unit from the intake manifold to the cylinder head. The 1967 and older cylinder heads do not have this tapped boss, 1968 cylinder heads do but even the, some were cast with the boss but not drilled. The casting number 3917291 cylinder head is the only one of the three "camel hump" heads to have this feature.

 
In 1969, Chevrolet went from a 'short' water pump to a 'long' water pump and move the alternator from the driver-side of the engine to the passenger-side of the engine. This change necessitated a change in the cylinder head to accommodate the new alternator mounting braces. Some late 1968 heads may have the bosses but are not drilled and tapped.

In 1971 most small block Chevrolet engines began using tapered seat spark plugs. Older small block Chevrolet engines used a spark plug with a flat set and compression washer. The spark plug wrench size also changed from the early 13/16" to 5/8" on the tapered seat spark plugs. Cylinder head castings were changed as well so you need ot ensure you use the correct spark plug.

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