Django model inheritance on other model's field
===

I have the following models:

    class Engine(models.Model):
        ...
        def speed(self):
            return 100
        objects = InheritanceManager()

    class TurboEngine(Engine):
        ...
        def speed(self):
            return 500

    class Car(models.Model):
        ...
        engine = models.ForeignKey(Engine)

No I am using a DetailView on a `Car` with a `TurboEngine`, but `car.engine.speed()` returns 100. How do I make it select the right class?