Have this idea in my head that there must be an ambient HP that drives a Prius, and I'm attempting to figure that out based on the fuel burn. My Prius in my hands for my conditions achieves 4.3 Lt/100km. Lt per 100 km 4.3 US MPG 54.7 IMP MPG 65.69 KM per Lt 23.26 Now if I knew what the fuel efficiency of the Prius engine was I could make a simple math calculation to determine HP per Hour. In older aircraft speak would see 0.5 lbs of fuel burned per HP per Hour, but more modern car engines do better than this. If I assume 4lb per HP per Hour I think I would be around the median of useful figures. Based upon this: 4.3 Lt per hour converts to 4.3 x 0.737 = 3.169 Kg fuel per hour or 6.98 lbs. Now it is simply 6.98lbs/0.4 = 17.4 HP I wonder would anyone care to make any advances on that, or just check out the reasoning (if there is any ).