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I have a 3 1/2hp oilless. Bought it used 14yrs ago. It's deafening (can hear it inside the house through the shop wall and the house wall with the shop 30yds away), but it has never failed (well, the pump hasn't.. pressure switch and regulator died but I scrounged replacements). I'd like to have something quieter, but I have run the dog doo out of this thing and can't complain. It runs my rattle wrench, die grinder, oiler on my big mill, airs tires. My cutoff wheel is really the only thing that will instantly bring it to its knees. As for rated power vs real compressor HP, the motor rating in reality has absolutely NOTHING to do with it. Al manufacturers now rate their compressors with the motor for one simple reason. The bigger the number, the more likely you are to buy it. A 1hp compressor is 4CFM at 100psi. If the electric motor is a 3450rpm motor, you can count on about half the motor rating as the actual hp of the compressor. A bit less than rated if it has a 1725rpm motor. About 3 engine hp per compressor hp if it is gasoline powered. Oilless seem to be even less efficient than piston types. I think that lost efficiency must be converted into noise. To this end, my 3 1/2hp is putting out about 8CFM at 90psi... less than 2hp. Now go down to Lowes or similar and have a look at that oilless 5hp 60 gal compressor. Big tank and a lot of plastic on a compressor that is maybe 3 actual hp.
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