There have been some Aussie developed steam cars in the past that turned some pretty respectable mileage and performance figures...never made it 'though.
Was looking at some 3,000 HP steam turbines yesterday at an overhaul facility. 3,000HP at 6,000 shaft RPM, with two stages of rotating blading around 2 feet in diameter (blade height above the disk was around 1.5-2".
Not really suitable for street use...the system described would be lucky to achieve 15% thermal efficiency. (My 625,000 and 900,000 hp machines are mid 30s and low 40s respectively)