Blast resounded round exhaust's opening in backfire (9)
I believe the answer is:
boomerang
'backfire' is the definition.
(I've seen this before)
'blast resounded round exhaust's opening' is the wordplay.
'blast' becomes 'boom' ('boom' can be a synonym of 'blast'**).
'resounded' becomes 'rang' ('ring' can be a synonym of 'resound').
'round' means one lot of letters goes inside another.
'opening' suggests taking the first letters.
The first letter of 'exhausts' is 'e'.
'boom'+'rang'='boomrang'
'boomrang' placed around 'e' is 'BOOMERANG'.
'in' acts as a link.
(Other definitions for boomerang that I've seen before include "Backfire" , "Primitive weapon" , "Curved throwing stick" , "Aboriginal throwing stick" , "Aboriginal weapon" .)