[BruceWilkie]

Something to keep in mind about head flow. NA its a matter of VE at a given rpm. Amount of flow capacity determines rpm point for peak power. Once you hit that point it becomes more difficult to make more power above that RPM.

Boosted engines, head flow capacity greatly determines what pressure would be required to move more than 100% VE at whatever rpm you chose to limit yourself. Mass airflow. Want 1500 hp? Then you need about 150 lbs/min airflow. If the turbo is up to it it can supply it.

Boost psi on the gauge is a measure of restriction. What pressure are you going to end up with to flow 150 lbs/min air?

The higher flow capacity head will move that 150 lbs/min at a lower pressure vs a more restrictive head.

With pressure comes charge heating. More psi for a given flow amount can still make same power up to the point charge heating affects preignition/detonation for the fuel being used.

Three examples 1500 hp. All three combos need 150 lbs/min airflow to acheive 1500 hp

455 6x head ported to 260 cfm. Its going to take a tid over 5700 rpm to use 100% CAPACITY of that 260 cfm NA! basically 100%ve.
What Boost pressure would it take to move 150 lbs/min air???

Nearly 29 psi on the boost gauge MINIMUM pressure.

535 370 cfm head. NA its going to take a tid over 6900 rpm to reach 100% capacity. At 6000 rpm you could potentially have a capacity of 15.5% above 535 cid at 6000 rpm.(115%ve potential)

So now what does MINIMUM boost pressure for 150 lbs/min airflow look like??

About 15.8 psi MINIMUM on the boost gauge.

Now lets put the 370 cfm head on the 455 and set rpm at 6000 rpm. 1500 hp goal.
Still needs 150 lbs/min airflow from the turbo.

At peak power whats the boost gauge going to read?

Now you are looking at 135.8% flow potential capacity over what the engine could consume 100% ve.

SURPRISE! Same as the 535! 15.8 psi minimum to move 150 lbs/min air through them.

Why? SAME FLOW CAPACITY.

The 535 will still be a better package. Better low speed and transient response, faster spool up etc. (greater liklihood of a turbo match as well)

So with boost pressures likely higher than estimated because your not likely going to be as close to those potential VE capacities to start with regardless, do you want 15.8 psi or 29 psi MINIMUM to do the job?

Which is going to be more fuel sensitive and preignition/detonation prone?

PLEASE NO HATE MAIL these are approximate GUESSTIMATES as there are many other factors to consider. I just wanted to illustrate the effect of head flow capacity on boost psi vs airflow through an engine.