[londons_explore]

Those things also don't need 400psi.

A modified fridge compressor could have 4x the capacity at 100psi and be suitable for a small workshop.

[mnouquet]

Do you understand the concept of air flow at a specific pressure ? 15CFM at 90psi is no small feat.

Lowering working pressure does not increase CFM, pump have a fixed displacement at their most efficient RPM, it's not gonna change...