Genuine Balboa Ultimax / Ultima / Vico Spa Jet Booster Pumps. This replaces the 2HP 3HP, and 4HP 2-speed pumps. Both 1 and 2 Speed versions available. These supersede the older  pumps. Balboa Water Group GG Industries. Comes standard with AMP plug. 

Replaces superseded part numbers: 1023021 ,1023033 ,1023034, 1023324, 1038105, 1038305, 1038301, 1038403, APUM40253A and others.

Versions:

•  (Labelled 1.5HP) (uncommon)

Installation Notes if Replacing a SuperWow pump:

• Use on pump thread due to a variance of the thread. Newer pumps have a tigher thread.
• Plumbing side is very similar, but in some cases it will need to be modified.
• Motor mount is different. Remove mounting studs in spa and mount motor as necessary.

Balboa Pumps marked "4HP" & "3HP" are actually a 2HP pump in Australian spas. See notes below for explanation. 

Ultimax (current) vs SuperWow (obsolete):

These are a very common pump found on many Spa Industries' brands of spas. (Bullfrog, Signature, Leisurite, Designer, Lanark, SCS Industries, etc)  They were often 2-speed pumps with the low-speed wire clipped off, thus actually becoming single speed pumps. If your plug has one wire clipped off, ensure the new pump has the same done! 

Dimensions:

• 2HP / 3HP / 4HP Two-Speed: Length: 395mm / Height: 197-232mm / Width: 168-195mm
• 2HP / 3HP/ 4HP One-Speed: Length: / Height: / Width: 195mm
• 1.5HP Two-Speed: Length: / Height: / Width: 195mm
•  - measures ~78-79mm OD on pump

Notes about Horsepower Ratings: 

• Some Spa Manufacturers use a complicated & confusing form of Horsepower measurement that was more commonly used in the USA, called hydraulic horsepower (HP=PSI*GPM/1714). It gives a more impressive appearance, and may give a false impression of performance. 
• Standard Australian HP ratings are calculated purely on input power in Watts, which are then converted to HP. (1HP=745.7Watts). 
• You can always measure (with an Amp Meter) the input current and convert back to real HP.
• Rough HP measurement can also be calculated using Ohm's Law (V=IR).  These pumps also have an Amperage rating that can be roughly converted back to Watts, and then to Horsepower. The problem here, is some spa manufacturers used slightly misleading ratings here as well, eg, they'd use a locked-rotor Amperage draw, etc. You'll see how the Amperage ratings and the HP labels don't match up.
• Furthermore, HP ratings are not an ideal measurement of pump performance anyway! Pump flow curves, which measure flow per metre of head pressure are a far more reliable method of measuring pump performance, especially with the advent of variable-speed DC motors.
• Basically the labels can appear to be very different in regards to the pump's actual HP rating.

Part Numbers: 1023033, 1023034, 1023073, 1025013, B- 1023034, B-P528226

UM EME 4HPR 2S / UM SI 3.0HPR 2S

Warranty: 1-year return to base. Excludes chemical damage, dry-running, etc.