Spread silence by blocking F1 race at the finish (4,5)

'race at the finish' is the definition.
I know nothing about this answer so I can't judge whether this works.

'spread silence by blocking f1' is the wordplay.
I cannot really see how this works, but
'spread' could be 'paste' (synonyms) and 'paste' is found in the answer.
'silence' could be 'sh' ('sh' is said to tell someone to be silent) and 'sh' is found in the answer.
'f1' could be 'f' and 'f' is found in the answer.
A single letter 'i' remains which might be clued in a way I don't see.
This explanation may well be incorrect...

Can you help me to learn more?