[Christ]

It also creates a larger plenum area, which means slightly more air available for higher RPM operation.

I'm also pretty sure that lengthening a tube while keeping the same diameter increases air velocity, though I might be wrong on that.

Anyway, if it does increase air velocity, that would mean better atomization, as there would be more turbulence in the air, which might make better power/economy.

AFAIK though, the biggest gains are seen in the higher RPM bands (mid-range torque and higher HP) due to the extra volume of air in the plenum.

As an add-on to this - Using thermal plastic to make an intake manifold will net you better HP and TQ as well, due to the temp differential (thermal plastic allows the incoming air to cool the intake manifold, as opposed to the cylinder head heating it... air temp decreases and you get better throttle response and HP)