Here's one dynamic which is usually not considered in these "size" calculations. That is the quality of the air flow at these higher lifts.
So we've got intake valves that are the biggest that can be stuffed into the available intake valve space. Only .06" bigger than the normal valves. Exhaust valves that are similarly the biggest possible. Both of which leave the real estate between them as very minimal. As flow bench tests indicate more air flow potential with them.
Now consider the air flow at various lift values of the valve. Does the flow start strong at .100" or does it take .400" before it really comes alive, compared to a stock head? All of these comparisons affect total cylinder filling capabilities. More air at the lower lift points will better fill a cylinder than huge flows at the .400" lift point, by comparison. Which means that "less cam" can be possible, with better street driveability and a possibly broader torque curve.
On the other hand, a faster lift curve (which can be assisted by the higher-ratio than stock rocker arms) can get the port to "full volume" quicker, which might help with a controlled turbulance in the chamber itself.
Big ports also aid the high-lift flow, but can result in "lazy flow" at the lower lift and rpm levels.
When you look at the combustion dynamics research in the middle 1950s (when the "modern" V-8s were being designed), one of the strategies was "stratified charge", where the richest mixture would be near the center of the chamber, hopefully where the spark plug was located, easier to fire-off, which would then fire-off the outer rings of less-dense fuel in the chamber. Which resulted in the later swirl strategy of the 1980s. Seems like Ford was one of the operatives in this research, according to magazine articles on such?
The Ford Y-block V-8 was a competive engine to the Small Block Chevy, but the Ford only achieved it's potential with a supercharger on it. Why? Intake valve shrouding, which was probably there to induce "swirl" into the chamber. As the Chevy V-8 was enlarged, valve sizes also increased, as possible. But when the breathing needs resulted in the famous 2.02" intake valves, little additional flow resulted. UNTIL an additional cut was made to help un-shroud the intake valve to the "close side" of the combustion chamber's edge. Which was done at the factory, on the same castings as the lower-performance cylinder heads. So, it was that extra cut that helped the larger valves to make more real power in the higher rpm levels the engine was capable of.
Not unlike the "clearancing" of the upper cylinder bore to put 340 heads on a 318, as mentioned in the LA Engine Race Manual, as I recall. Not a huge amount, and certainly above where the compression ring rides at the top of the bore, but still needed for the "large intake valve" clearance.
So, my point is, that unless the larger intake valve is completely unshrouded, compared to the stock size 2.08 intake valve, the real advantage of the larger valve might be lost, or not used to its possible full potential. I also understand that in many race applications, just 2 more horsepower might make the difference between winning and not. But considering the approx 20% power absorption of the drivetrain past the flywheel, such power increases on the dyno might become less significant in real performance increases.
Better getting a handle on combustion chamber turbulance has been a focus of engine designes for many years, now. Understanding and compensating for such things means that the air in the chamber, as the piston moves upward toward TDC, prior to the "big bang", keeping more of the fuel in suspension, makes for more horsepower and fewer exhaust emissions via a more complete burn activity. Which can also mean less fuel in the fuel curve for enahced efficiencies, for equal or more power output.
In later years, it appears that when the intake valve opens has been modulated a bit, compared to earlier times. The same might be true of when the exhaust valve opens, too.
Yet the best intake ports and exhaust ports can't work well unless what the exhaust flow encounters "after the fact" also works well. With the end result being less reversion (and internal EGR) in the chamber during "overlap", which due to pressure pulse reversion in the intake manifold, can dilute any fresh intake charge entering the combustion chamber.
Exhaust port deficiencies can be compensated for with more duration on the exhaust lobes, up to a certain point. To me, when looking at cam specs and rocker ratios, it can become evident when an exhaut port is not as good as it should be when you see much longer (than generally accepted as "normal") exhaust duration and higher rockder arm ratios. Although the rocker ratios can be a desired compensating design factor for a desired lower-lift cam lobe situation, by the engine's design team. This can also be a way to get the valve open quicker, too, if the ports might not flow too well at lower lifts, I suspect. There can be a few other dynamics in using higher-than-designed rocker arm ratios too, fwiw.
Better quality of air flow/turbulance in the combustion chamber could well be better than just going for max flow numbers on a flow bench. Size can matter, but sometimes too much can result in less benefit than suspected, compared to "the norm" of factory specs.
I'm fully aware that Chrysler recommended the larger valves, many decades ago. But I suspect that in later times, the larger exhaust valve (with increases in port flow) by itself, in concert with a better total exhaust system past the cylinder head, might be a better way to do things. Just my theory of things.
Enjoy!
CBODY67
