Ion propulsion?
Remember, those things have TINY amounts of thrust. Not enough to make the car move, never mind at high speeds. The only reasons space probes can reach extremely high speeds with them is because there is no gravity or atmosphere to slow them down, and even then it takes quite a while to build up speed.
Even at high altitudes, it would barely budge.
Maybe liquid-fuel rockets...
Or ramjets if you can go fast enough... And are crazy enough...
