Reply to "351C cylinder heads, open chamber vs closed chamber"

Derek, focusing on the 351C 4V motors with self adjusting (hydraulic lifter) valve train manufactured in the US from 1970 through 1974 there are 3 distinct motors.

1) the 1970 and 1971 351C 4V, had closed chamber heads with 2.19" & 1.71" size valves, an engine block with 2 bolt main bearing caps, a very mild cam shaft, a 600 cfm Autolite 4300A carburetor, a very light harmonic balancer, and cast flat top pistons. Ford rated the compression ratio at 10.7:1, but it was actually about 9.5:1. The ignition consisted of a single breaker point distributor. The motor was rated at 300 bhp in 1970. That year, AK Miller, one of Ford's own contractors, tested a production motor and found it produced only 288 bhp. The results were published in Hot Rod magazine, so the following year the motor was rated at 285 bhp.

2) the very late 1971 through 1972 351 Cobra Jet, had open chamber heads with the same 2.19" & 1.71" size valves as the previous motor, an engine block with 4 bolt main bearing caps, a Cobra Jet camshaft having specifications identical to the FE 390GT & FE 428 Cobra Jet motors, a 750 cfm Autolite spread bore 4300D carburetor, a decently heavy harmonic balancer, and the same cast flat top pistons as the earlier motor. The compresion ratio was accurately rated by Ford at 8.8:1. The ignition consisted of a dual breaker point distributor. This motor was rated at 280 bhp. This motor ran stronger and rev'ed higher than the earlier motor.

3) the 1973 through 1974 351C 4V motor was actually a Cobra Jet motor, Ford simply reverted back to calling it a 4V. This motor differs from the 1972 Cobra Jet in 4 ways. The 2.19" & 1.71" size valves in the open chamber 4V head were replaced with the 2.04" & 1.65" size valves of the 2V motor; the camshaft timing was retarded 4 degrees; dished pistons replaced the flat top pistons, resulting in a drop of the compression ratio to a dismal 8.0:1; and exhaust gas recirculation was added to the motor, evidenced by an "EGR plate" sandwiched between the intake manifold and carburetor. This motor was rated at 264 bhp.

Your friend on the DTBB, George