Modern cam lobes have faster rate ramps. The ramps are where clearances are taken-up in preparation of opening the valve; and where setting the valve back on its seat occurs as the valve closes. A faster rate also equates to a shorter ramp length or duration. Modern cam lobes also have faster lift-rate flanks … the flanks of a cam lobe are where the opening and closing of a valve take place. High lift no longer requires long duration as it once did.
Aftermarket cams are generally ground with narrower lobe centers, thus torque curves are steeper and power bands are narrower. The cams imbue engines with lopey idles, the steeper torque curves react more vigorously to the throttle, and therefore burning rubber is easier … sometimes unavoidable.
Supposedly that's what SEMA customers want, or at least that's what SEMA advertising and Hot Rod magazine have people convinced they need.
The needs of a 351C with 4V heads are different than the needs of a 351C with 2V heads. But this is not unique to the 351C. Explaining why will help in understanding the peculiar needs of the 351C with 4V heads.
When federal emissions regulations took effect in 1968 they impacted 3 aspects of an engine … the carburetors were tuned for leaner air/fuel mixtures; the compression ratios were lowered; AND the camshafts were designed for less duration and overlap. These things were done to lower hydrocarbon emissions, carbon monoxide emissions, and emissions of the nitrides of oxygen (i.e. NOx).
The manufacturers initially responded to the federal regulations with plans to work around them and continue building performance cars. So the manufacturers developed heads that didn't rely upon long duration cams in order to have high rpm power bands. Chevy developed rectangular port heads for their big block Mark IV engine. Pontiac developed big port heads for their 350/400/455 engines. Chrysler's new performance heads had bigger valves, open combustion chambers and larger ports. Ford developed the Cobra Jet heads for the Big Block 385 series V8. And Ford also developed the 4V heads for the 351C. These “big port” heads allowed those engines to develop high rpm power bands while using short duration low overlap cams. This is a unique group of engines that "in general" the SEMA crowd doesn't understand. The extent to which cams are designed to meet the needs of these special engines varies from engine to engine. Comments about these engines however are more or less the same … the ports are too big … and it’s easy to over-cam them.
Unfortunately the SEMA industry has many enthusiasts believing all engines are the same. They reject engines that don’t fit the mold, rather than accept the fact that their methodology doesn’t apply to all engines. That “mold”, i.e. the average engines which SEMA caters to, are akin to the small block Chevy. They have inherently low rpm power bands; they require long duration cams, more overlap, and dual carburetor or single plane intake manifolds to get them to rev higher. The "big port" engines however were designed differently. They have inherently high rpm power bands. Performing the same modifications to big port engines that are normally applied to low rpm engines drives the power bands of the big port engines too high … and drivability suffers. Then the engine is blamed instead of the methodology of the mechanic.
Modern high lift – short duration camshaft lobes work fabulously with the late 1960s – early 1970s big port engines. But even when increasing valve lift alone an engine’s power band shall be pushed to higher rpm, in a manner similar to increasing a camshaft’s duration. So limitations arise.
In regards to camshafts for the 351C with 4V heads, to take advantage of modern cam lobes, to "improve performance in a civilized fashion" as you put it, I find it necessary to have camshafts custom ground to my specs. I keep the torque curve flat and wide with wide lobe centers (I use 114 degrees these days) which makes the power easier to control, and I keep the duration and overlap short to avoid pushing the power band any higher than it already is. But pushing the power band higher is inevitable. For instance peak horsepower occurred at 5800 rpm with the factory cams (the 351 Cobra Jet had 0.481 gross lift, the 351 Boss had 0.477 net lift), while with 0.580 inch gross lift (0.570 inch net lift) peak horsepower occurs at 6500 rpm.
A Cleveland should be rev limited at 6200 rpm unless high rpm durability improvements are performed. Peak horsepower occurs at 6200 rpm with gross valve lift at 0.530". So unless a person is willing to spend the money performing the needed high rpm durability improvements, it doesn't make sense to install a cam with more than 0.530 lift. The factory rocker arms are known to cause accelerated valve guide wear when used with high lift cams. So 0.530 lift is a good limit for the factory rocker arms too. AND … with 0.530 lift an engine with a single 4bbl carburetor will make about 410 net horsepower. It just so happens that 410 net horsepower is near the limit of the factory fuel system to supply fuel. So there's quite a point of convergence for 0.530 lift and 410 horsepower. From that point onward the dollars multiply quickly.
Of course, those Webers your engine is equipped with raise volumetric efficiency, so for any given set of parameters, your engine would make more horsepower than an engine equipped with a single 4bbl carburetor.