The problem is air volume. Regular air compressors do not provide enough volume of air.
A typical Chevy 350 engine may require 600 cubic feet per minute at full throttle. The compressor would have to supply MORE than this in order to produce any pressure in the intake manifold.
Now. imagine a box 1 foot x 1 foot x 1 foot, with air inside. Now imagine 10 of those. This 350 cid engine uses 10 such boxes of air
each second. That's a lot of air.
A typical larger shop - type compressor flows about 5 cubic feet per minute, not 600.
You would simply need a huge compressor with a big pipe to flow so much air.
Here is a better idea:
I considered using my big backpack-style gas-powered leaf blower (the kind that professional landscapers use, not a cheapo hand-held unit)
Like this one.
(click)
These units can blow about 1200 cfm at minimal pressure. My guess is at about 400 - 600 cfm, they can produce about 2-3 psi or so.
The outlet pipe was about 4 inches dia, or about the same size a the intake on an efi 2.3 liter Mustang I had.
I had considered experimenting with pressurizing the intake with this leaf blower for more power, but never got around to it.
Also, I had considered using a 12 volt cordless 400 cfm blower, so I could make an under-hood unit for smaller engines. One could rig it up so the blower would come on at wide open throttle only. However, I probably would have gained only a few HP at best.