The longer stroke has a very specific application on the Elio Gonna be a bit long winded, but work with me here. I need to start with the aerodynamics (I'll get to the point, I promise) The Elio has roughly half the drag of the 1996 Geo Metro (5 speed manual 1.0 3 cyl), a car that is commonly used for comparison. This is very important. Let's Say: Elio at 30 mph has 1 unit of drag Geo Metro at 30 mph has 2 units of drag The units are unimportant for this argument, measure them in lb or kg of resistance if you will. Double your speed and the drag increases by 4 fold (use the K = ½mv2 if you must) Elio at 60 mph has 4 units of drag Geo Metro at 60 mph has 8 units of drag So an engine designed to be efficient in a Geo Metro at 60 mph (with a specific gearing, and stroke) would actually be LESS efficient in an Elio (measured in thermal efficiency) This is where the length of the stroke of the piston comes into play. Definitions: Torque: power per impulse Horse Power (Watts or Kilo Watts): Power per impulse multiplied by rate of impulses (RPM is a factor here) A short stroke engine will produce less work per impulse but typically make an engine that allows a higher RPM with the same technology. The power curve will show less HP at the lower RPM's but, due to the higher RPM, it will produce more HP at the high end. A long stroke engine will produce more power at lower RPM's helping acceleration but be limited on the high RPM's thus limited on the rated HP. Most drivers rarely make maximum horsepower which is measured at best rate RPM AND open throttle. This brings me back to aerodynamics. The Elio aerodynamics require less work to be done at speed. This allows a longer stroke engine to provide good acceleration without the NEED to have additional HP at the higher end. Thus 55 HP may seem paltry, it's actually sufficient due to the power curve of the long stroke engine. This would actually explain the drop from 65 HP to 55 HP during the development of the engine. Keeping this in mind, it is likely that the Elio will actually be "peppy" and fun to drive opposed to the sluggish nature of the Geo and more modern Prius C Stay tuned for our next lesson: A longer stroke does not necessarily mean a higher compression ratio.