Pidyon Haben

Pidyon Haben Everybody knows, eating at a Pidyon Haben is like fasting 84 Taniyos. 
 The Sdei Chemed writes, there is no such Mekor anywhere. Most Poskim don’t consider a Seudas Pidyon Haben as a Seudas Mitzvah. 
 The Ostrovtzer Rebbe ztl said that it is “ Keilu “as if, he fasted. A “Keilu fast only works on “Keilu Aveiros” and not for the real Aveirah. (Kol Hador Bechul Keilu Oved Avoda Zarah etc.) 

 The Rebbe said, we find in Shas, 84 such Keilu Aveiros. 

 R. Yosef Chaim Zonenfeld ztl . said learning a blatt Gemoro works just as well as eating food from a Pidyon Haben. Daf has the osiyos Pei Daled = 84.