1968 Chevy 307 Specs
by Richard Rowe
Introduced in 1968, the 307 was a typically muscle-car-era response to squeezing more power out of a small displacement engine. Essentially a 283 block with the crankshaft and rods from a 327, the 307 served duty as Chevrolet's smallest small-block V8 until it was replaced by the 305 in 1973.
Power
When it was introduced in 1968 the 307 was rated at 200 horsepower at 4,600 rpm and 300 foot pounds of torque at 2,400. However, the federal government's emissions regulations of 1972 saw the 307 de-rated to 115 horsepower. While a certain amount of this was due to testing standard changes from "gross" (just the engine with no exhaust system) ratings to "net" ratings (power measured with exhaust system, intake system, alternator and all accessories), post-1972 engines were still down about 60 horsepower when compared to earlier years. Chevrolet never produced a high-performance 307, but it did offer a marine version of this engine rated at 245 gross horsepower.
Lower Engine
The 307 used a 283 block with casting numbers 3914635, 3932371, 3932373, 3956632 and 3970020. The block used 3.875-inch cylinder bores, 5.7-inch rods and a 327 crankshaft with 3.25-inch arms (casting numbers 39110011 and 31110001). The 307 crankshaft used the same main and rod journal diameters as the 1968 327 -- 2.45 inches and 2.10 inches, respectively. Compression varied between 8.2:1 for emissions-era motors, to 9:1 for earlier engines and upward of 10:1 for marine engines.
Cylinder Heads
The 307 used one of three cylinder heads -- casting numbers 3927185, 3986338 and 3998991. Casting numbers 3927185 an 3986338 are early low-rpm torque makers with 70-cc combustion chambers, 1.72-inch intake and 1.5-inch exhaust valves. Chevrolet used the 3998991 from 1970 to 1976, and it was identical to the other heads except for its larger 74.56-cc combustion chamber.
Manifolds
The 307 used one of three cylinder heads -- casting numbers 3927185, 3986338 and 3998991. Casting numbers 3927185 an 3986338 are early low-rpm torque makers with 70-cc combustion chambers, 1.72-inch intake and 1.5-inch exhaust valves. Chevrolet used the 3998991 from 1970 to 1976, and it was identical to the other heads except for its larger 74.56-cc combustion chamber.
References
Writer Bio
Richard Rowe has been writing professionally since 2007, specializing in automotive topics. He has worked as a tractor-trailer driver and mechanic, a rigger at a fire engine factory and as a race-car driver and builder. Rowe studied engineering, philosophy and American literature at Central Florida Community College.
