I wasn't sue where to post this, but since this is potentially applicable to dirtbikes, I put it here. Feel free to move, if appropriate. So, when I first heard about a 6-stroke engine (a few days ago), I thought it was a joke, but they really exist (at least in theory) and fascinate me. I don't remember where I heard about it (hope it wasn't on TT). Anyhow - here is a description (stolen from link): https://en.wikipedia.org/wiki/Six-stroke_engine The term six-stroke engine has been applied to a number of alternative internal combustion engine designs that attempt to improve on traditional two-stroke and four-stroke engines. Claimed advantages may include increased fuel-efficiency, reduced mechanical complexity and/or reduced emissions. These engines can be divided into two groups based on the number of pistons that contribute to the six strokes. In the single-piston designs, the engine captures the heat lost from the four-stroke Otto cycle or Diesel cycle and uses it to drive an additional power and exhaust stroke of the piston in the same cylinder in an attempt to improve fuel-efficiency and/or assist with engine cooling. The pistons in this type of six-stroke engine go up and down three times for each injection of fuel. These designs use either steam or air as the working fluid for the additional power stroke.