I've got a new craftsman 5.5 hp, 30-gallon air compressor. It is capable of 6.4 SCFM at 90 PSIG. I just bought a 25-400 ft/lb impact wrench. The box said its minimum requirements were 4.0 SCFM at 90 PSIG. However, the instructions inside the box says 8.0 SCFM at 90 PSIG is needed.
If my compressor will not be able to power it to the full 400 ft/lbs, I'll return it for a cheaper model that I could fully use. A 25-225 ft/lb version from craftsman exists and it is $40 cheaper.