Doesn't matter how fast they spin. It's how much positive pressure they can generate. Thomas Knight's motors had a 15 hp draw. That's about what it would take to make positive pressure on a modest four-banger. (Indeed, their dynos showed that boost petered out at higher rpms on the 2.4 liter Altima they used as a test car.
5-7 kW might just cut it... probably enough to give your Jeep around... 5-6 psi of boost...
...the question is how much weight in capacitors or batteries you're willing to carry around?
