[cleanspeed1]

Let's take a look at the differences between the 4.6 Modular ( 2V ) and the 5.0 Ford.

Reduced bore for lower emissions

Low fiction valvetrain

Low friction piston rings

Undersquare bore to stroke ratio

Fast burn combustion chambers, small valves and ports for high velocity

Long runner intake manifold

For economy, the closer you can keep it to stock, the better it will run because it was optimized from the factory to run in the lower ranges most of the time. Anything that enlarges the ports lowers the velocity of air into the port at lower rpms, unless there's a displacement increase or some form of supercharging. Headers are not bad if they are built for no compromise in tube size and length, along with collector dimensions.

Cam timing, overall tune and gearing are the arbiters.