Look for the smashed up cars in Manhattan Noir.
Blow up the silver car, and build its pieces into a deflector base.
Now you just need something to deflect. Take out the two goons guarding the Kingpinlike car, and build a power source out of their still-warm remains. This will start the the car's turret firing.
Hop on the deflector base, and aim the fire back toward the gangster car- disabling it, and popping a gold brick from under the hood.