The skinny on compressors is that the data plates lie. Really.
I really like it when I hear a guy has a 5hp compressor motor that runs on 110V/20A wall circuit (nope, no way.. math says so) or quote the CFM of the compressor like THAT means anything.
Here's a guide that will get you close:
MOTORS:
5hp motor will need a 220V/20A drop
7hp motor will need a 220/30A drop
If you plug it into 110V outlet its of no real shop use.
Mag starts will help, but I've run my 5hp motor off the pressure switch (as long as bugs don't crawl into the contacts)
PUMP:
No real pump is gonna have less than two cylinders. If its a one lung pump consider it less than 5CFM actual air and useless for shop use.
If it's 'oil less' its useless for shop use.
Should turn less than 1000-1500 RPMs for quite operation and long life.. pulley should have a built in cooling fan, cylinder interconnects also should have cooling fins.
Have an unloader and ball bearings, not bushings on the crank.
My pump it 14CFM (
http://www.eatoncompressor.com/catalog/item/518643/184117.htm) with a 5HP (true) Baldor motor and I use it for everything.. paint, sand blasting, body work (orbital sanders) and tools (impact, air ratchet) and with a 60gal receiver.
Total cost was about $600 (about 6 years ago) but you could put together a much better compressor from parts that you can buy in a store.
