I get that, Eric explains it in pretty much every video he does :) i was more curious that if someone (Me) is planning a 408 that won't be going over say 6500 (cause i'm a wussy that worries too much) would having 330 over 300 make much difference or does that extra cfm mostly matter to the guys that are running up well over 7k?
RPM is part of the puzzle. The first half of it, are you lifting the valve that high? If not, then you’re under using the head. The third thing is CID. The larger the port the higher you’ll need to rpm the engine to make good use of it
However, that doesn’t mean you can’t make good power with an under utilized valve lift vs the heads potentially excellent return. Same with cubic inch vs head volume and rpm vs port volume.
In other words, you would have to build a pretty unbalanced engine to put to much head on top but it is easier to do the reverse. An example would be something like, tiling a 408 with a stock head and giving it a 260@050 solid roller cam and expect a 9.0 slip. Not happening. Then the flip side. A stock 319 @ 8.7-1 with a fully ported W9 isn’t going to run 9’s ether.
The closer you are to a well balanced engine the better it will perform for the use you intend on and it’s is easy to achieve but the super fine combo is hard. You can screw together almost any combo and it’ll go. How well it will go is another story. One hour trying to zero in on and that’s impossible since all of our crystal balls are broken.
Another thing is you can slice and dice a combo to death. Try not to split all the last fine hairs on it. Just work at it over time. No matter what you build, there’s always room for improvement in someone eyes.