Absolutely final way to get petrol during part of Grand Prix? (4-4)
I believe the answer is:
last-gasp
'absolutely final' is the definition.
(last-gasp means at the last possible moment)
'way to get petrol during part of grand prix?' is the wordplay.
'way' becomes 'st' (abbreviation for street).
'to get' means one lot of letters go next to another.
'petrol' becomes 'gas' (synonyms).
'during' indicates putting letters inside.
'part of grand prix?' becomes 'lap' (a lap of a race course).
'st'+'gas'='stgas'
'stgas' going inside 'lap' is 'LAST-GASP'.
(Other definitions for last-gasp that I've seen before include "'Final breath (4,4)'" , "Done at the latest possible moment" , "Finalk expiration, moment of death" , "Done in desperation at the final moment" , "Remnant of energy or final exhalation" .)