351C 2V vs 4V heads — where each one actually wins

Engine dyno, as configured — flywheel horsepower. Standard test config: stock manifolds through 18" of pipe, air cleaner lid flipped, no accessories driven. Factory SAE net ratings are measured as‑installed and read 15–25% lower. Rev ceiling for this combination: 6000 rpm.

Where each one wins

Torque, lb-ft, at the flywheel. Everything except the part named is identical between the two runs.

Everybody repeats that the 4V ports are too big for the street. Almost nobody puts a number on it, so here is one.

On a flow bench the 2V actually out-flows the 4V until about .350" of lift — 142 cfm against 116 at .200", 189 against 163 at .300". The 4V only pulls ahead once the valve is off its seat far enough to use those ports, and then it never stops climbing while the 2V goes flat at about 199.

That crossover is what the table below shows in torque. The 2V leads everywhere your street car actually lives, the 4V takes over up top and wins peak horsepower. Which one is "better" depends entirely on where you drive it.

One honest caveat: nobody has ever published a controlled 2V-versus-4V dyno swap on one Cleveland short block. This is computed from the measured flow curves, not copied off somebody's sheet.

The build

The other one

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