Race, as an engine (3)
I believe the answer is:
rev
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">race as an engine</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for rev that I've seen before include "vicar?" , "Clergy title" , "Minister" , "Gun (an engine)" , "Clergyman, or woman (abbr)" .)