I was lead to believe that crumple zones (which British vehicles have been required to have since about the 1970s) improve safety for the occupants of the vehicle by making collisions last longer, therefore reducing the peak deceleration experienced i.e. the force, making the collision more survivable.
Mass-produced vehicle parts can be replaced relatively cheaply. Dead people can't be resurrected.
It's amazing what you can achieve when you stop restricting the flow of exhaust gasses to the point that the engine has to fight against the backpressure of its own waste products.
Could you dump some of the waste heat in the exhaust into a heat-exchanger to reduce the back pressure? Analagous to condenser on a steam turbine?