Car manufacturer’s obsession with endless space up top (7)
I believe the answer is:
bugatti
'car manufacturer's' is the definition.
'obsession with endless space up top' is the wordplay.
'obsession' becomes 'bug'.
'with' says to put letters next to each other.
'endless' means to remove the last letter.
'space up top' becomes 'attic'.
'attic' with its last letter removed is 'atti'.
'bug'+'atti'='BUGATTI'
(Other definitions for bugatti that I've seen before include "Ettore -, It. racing car designer" , "Vintage car" , "classic racing car" , "Twentieth century Italian sports-car company" , "Italian racing car pioneer" .)