sub load_defaults_for_model {
   my $self=shift;
   my $model_attributes = $car_models{$self->{Model}};
   $self->drive_type($model_attributes->{drive});
   $self->body_type($model_attributes->{body});
   $self->engine_cap($model_attributes->{engine_capacity});
}

sub new {
   my ($class, $model) = @_;
   my $new_obj = {
       .... build your object ....
   };
   bless $new_obj, $class;
   if (defined $model) {
      $new_obj->{model} = $model;
      $new_obj->load_defaults_for_model();
   }
   return $new_obj;
}