General Chevy Small Block V-8 Data - 3.75 Bore Family
|General Chevy Small Block V-8 Data|
|3.75 Bore Family|
|4.00 Bore Family|
|4.125 Bore Family|
|3.670 Bore Family|
|3.50 Bore Family|
3.75 in bore family (1955-1973)
The engine family from which all Chevy V8s from the big blocks to today's LS7 and LS9 evolved is 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 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 give rise to later small blocks and to the “W” blocks which would later give rise to the Chevy big blocks. The last of this family was the 307 which was a stroked 283 with a medium journal.
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-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 1955 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.
The 265 ci V-8 was bored out to 3.875 in (98 mm) in 1957, giving it a 283 cu in (4.6 L) displacement. 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. Power was up a bit each year for 1958, 1959, and 1960. The 1957 Ramjet mechanical fuel injection version produced an even 1 hp (0.746 kW) per cubic inch, an impressive feat at the time. Many tout this as the first US-built production V8 to produce one horsepower per cubic inch.
Besides being available in the Chevrolet line, it was optional in Checker Taxis beginning in 1965.
A 307 cu in (5 L) 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.
The 307 replaced the 283 (but are the same engine block with a longer stroke) in Chevrolet cars in 1968 and produced 200 hp (149 kW) SAE gross at 4600 rpm and 300 lb·ft (407 N·m) of torque at 2400 rpm in the 1960s. The later emissions-modified versions produced just 115 hp (86 kW) SAE net, giving the engine one of the lowest power-per-displacement ratings of all time. Chevrolet never produced a high-performance version of this engine, though they did produce, for Outboard Marine Corporation, a high-performance marinized 307, rated at 235 hp (175 kW) and 245 hp (183 kW) SAE gross, depending on year, that shipped with the Corvette/Z-28's cast aluminum valve covers and Rochester QuadraJet carb. Chevy also built other versions of the OMC 307 rated at 210 hp (157 kW), 215 hp (160 kW) and 225 hp (168 kW) SAE gross.