go ahead vs plunge in

go ahead

verb
  • To proceed with; to begin. 

  • Used to grant permission for or to give endorsement of a suggestion or proposal. 

  • To send communication over the radio. 

plunge in

verb
  • To start a new endeavor enthusiastically and wholeheartedly, though possibly without experience. 

How often have the words go ahead and plunge in occurred in a corpus of books? (source: Google Ngram Viewer )