Register a car of superior quality but not special (4)
I believe the answer is:
roll
'register' is the definition.
(I've seen this before)
'a car of superior quality but not special' is the wordplay.
'a car of superior quality' becomes 'rolls' (Rolls Royce).
'but not' indicates named letters should be taken away.
'special' becomes 's' (common abbreviation as in Special Air Service).
'rolls' with 's' taken out is 'ROLL'.
(Other definitions for roll that I've seen before include "Schedule" , "Press" , "Small rounded bread" , "Cylinder (of paper etc)" , "Move by turning over" .)