Old race vehicle out of gas rounding port (7)
I believe the answer is:
chariot
'old race' is the definition.
'chariot' can be an answer for 'race' (chariot race is a kind of race). I am not sure about the 'old' bit.
'vehicle out of gas rounding port' is the wordplay.
'vehicle' becomes 'cat' (cat is a kind of vehicle).
'out of' is an insertion indicator (some letters on the outside of others).
'gas' becomes 'H' (chemical symbol for hydrogen).
'rounding' indicates putting letters inside (some letters go round others).
'port' becomes 'rio' (Rio de Janeiro is a port).
'cat' placed around 'h' is 'chat'.
'chat' enclosing 'rio' is 'CHARIOT'.
Can you help me to learn more?
(Other definitions for chariot that I've seen before include "former military vehicle" , "Two-wheeled horse-drawn vehicle in ancient Rome" , "Horse-drawn racing vehicle; oat rich (anag.)" , "American religious folksong 'Swing low, sweet ...'" , "Stately vehicle" .)