That compressor came off of a Speedaire 3JR76 unit that is sold by Grainger. If you can find an air compressor repair shop they should be able to help you. The motor on my compressor says SPCL where the HP should be. I can tell you that it's rated 230volt, 21AMP single phase and 3450RPM. Hope this helps.Yes it is ,4 cylinder but information I found says it is single stage. I am still looking for a electric motor to put on it. Building it for my son.
X2 on that, my 2 cyl, 2 stage Champion has a 5 hp 230v Baldor“SPCL” dates from the false advertising era. But 21 amp and 230 volt is going to be a 5 hp motor.
Electric motors have considerable overload capacity above their continuous rating, dishonest manufacturers were slapping that useless and totally irrelevant figure on the sides of their air compressors and vacuum cleaners, then hiding it on the motor nameplate with SPCL.