Frank with best type of car? (4-3)
I believe the answer is:
open-top
'type of car?' is the definition.
'frank with best' is the wordplay.
'frank' becomes 'open' ('open' can be a synonym of 'frank').
'with' is a charade indicator (letters next to each other).
'best' becomes 'top' ('top' is associated in meaning with 'best').
'open'+'top'='OPEN-TOP'
(Other definitions for open-top that I've seen before include "Lacking cover" , "(Of car) not having a permanent roof" , "Like some tourist buses" .)