Why can’t we use the heat from combustion to make cars more efficient?

Question

Can we use the heat to boil water to turn a turbine? Or would the water never cool enough to be used again?

What about using the heat to create pressure and then releasing the pressure to help move the fly wheel?

In: 1046

Answer 1

But we already do it.
Turbochargers harvest excess energy that comes out the exhaust and use it to pump more air into the intake, aiding combustion