- Small ports
- Small valves
- High turbulence combustion chambers
- Low overlap camshafts
- Short intake duration
- Advanced camshaft timing (early intake valve closing)
- Dual plane intake manifolds (carburetor)
- Smaller (650 cfm) carburetors
- Long runner intake manifolds (fuel injection)
However, based upon many decades of personal experience I strongly disagree that 4V cylinder heads are strictly for high rpm operation. 351C 4V motors were factory equipment in Torinos & Montegos that weighed 4000 pounds or more, equipped with automatic transmissions, low stall torque converters, and 3.00:1 rear axle gearing. In other words 4V cylinder heads are quite capable of providing good low rpm power, however when hot-rodding a 351C 4V one must understand the difference between a motor with 4V heads and other motors, and make intelligent choices based on those differences.
There are many paths to making 500 horsepower with a 351C, with horsepower peaking in the range of 6000 to 6500 rpm. Dual plane or single plane intake manifolds, 750 cfm carburetors, free flowing exhaust systems (special attention paid to the mufflers), 10.0:1 compression ratio, and cams that lift the valves in the range of 0.570" to 0.620".
-G