It depends on the thickness of the loin. Pops recipe says that if its thicker than 4 inches that it requires injecting. He said that 2-4 inches may require injecting. I've done some that were 3 inches+ without injecting but I like to cure for 3 weeks.
{copied from Pops instructions}
"Refrigerate 7 to 30 days, depending on thickness of meat.
Up to 2 inches, 7-10 days.
2 - 4 inches, 5 - 17 days, may require injecting to cure from the inside-out as well as from the outside-in.
4 inches and larger. 17 - 30 days, requires injecting.
Injecting - use a Morton's injection 4 oz. manual injection pump with the Broadcast needle."