It comes down to the efficiency of the head. Remember that all flow number CFMs are not created equal, but normally a 4v head will still always out perform a 2v head. That is why more modern heads are designed with 4v or 3v in the 2005 Mustang. If you look at the flow numbers of that head, intake is fine, but the exhaust is total crap (I wonder why that is?)
Typically a very good 2v head is in the 65% range, while a 4v head is in the 85% range (off the top of my head), this is where the difference is. Its not that boost increases this percentage, but given if your maxing out the power with a 2v head at a given rpm, timing, volume, flow rate, comp ratio, a/f, displacement, etc. What do think would happen if everything was equal and your head was more efficient? Your ECR will happen at a lower boost level, then you have to add more fuel, or take timing out for that same boost level. Its a dance between a lot of variables that a lot of guys do not understand.
That is what I was trying to explain in the other thread, with a 10.3 and a 4v head, that is not a very good starting point for boost. You would have to drop it to at least a 9.5:1 to add 8lbs of boost. Of course you can boost at 10.3, but your a/f is going to be pig rich, and your total timing is going to be very low, so what happens to your hp when that happens. Remeber you can led a horse to water
