hell-bent vs hell-bent for leather

hell-bent

adv
  • In a recklessly determined manner; determinedly, wholeheartedly. 

adj
  • Recklessly determined to do or achieve (something). 

hell-bent for leather

adv
  • determinedly recklessly, in a manner that lacks restraint. 

  • Synonym of hell-bent (“(recklessly) determined”) 

  • Synonym of hell-for-leather (“very fast”) 

How often have the words hell-bent and hell-bent for leather occurred in a corpus of books? (source: Google Ngram Viewer )