Broadcast in part relates to petrol heads (12)
I believe the answer is:
transmission
'broadcast' is the definition.
(I've seen this before)
'part relates to petrol heads' is the wordplay.
I cannot quite understand how this works, but
'part' could be 'ans' (ANS is an example) and 'ans' is found in the answer.
This may be the basis of clue (or it may be nonsense).
'in' acts as a link.
Can you help me to learn more?
(Other definitions for transmission that I've seen before include "A broadcast programme" , "The sending of a radio signal" .)