It's hard to consider a Ford Mustang as "dusty", but some of them
have been particularly weak, before the recent performance resurgence. What we have here is the Mustang in the NHRA Classification Guide with the worse performance factor of any year:

The 1987 Ford Mustang LX 140/88 I-4
This car has a whopping 30.38 factor in Stock, putting it in W/S or W/SA (At -561lb from shipping weight)
In Super Stock, the engine is re-rated to 100hp with a factor of 26.73. That puts it into SS/P or SS/PA (At -973lb from shipping weight)