When replacing an old worn out pump, keep in mind that the new replacement pump is of a different design ,and has much more pressure and flow than the old one. If you are replacing an old bronze 1 h.p. pump, you would only need a 3/4 h.p replacement, due to the difference in performance and design. When it comes to pumps, bigger is not always better.
Never install more than a 3/4 h.p. pump if your pool has 1 1/2 inch plumbing. The only exception to this rule would be if you have a T
installed in the line between the pump and filter to operate a pool cleaner.
If your pool is plumbed with 2 inch pipe you can use a larger pump, but it probably isn't necessary unless you have a lot of return lines, a long plumbing run, or a pool & spa combination.