Our every day engines may seem fine but in fact, their efficiency is dreadful. Engines in our cars are, at best, 25% efficient. Half (50%) of their fuel energy is dumped in their exhaust. Gas released by an Otto engine's exhaust valves is extremely hot, typically at over 2,800 degrees Fahrenheit and 100 pounds per square inch. Put another way, the 200 advertised HP engine in your family sedan engine wastes 400 HP of energy in its exhaust. Mechanics know that the exhaust manifold of a gasoline engine often runs at a red heat, but few people know that a Ford Triton exhaust manifold is specified to withstand 1,900 degrees F., far above a red heat.
Otto engines also have large losses called throttling losses which occur when operated at less than full throttle. Anyone who drives a car knows that most of the time, one must run at reduced throttle to negotiate dense traffic and comply with speed limits, an inefficient mode for the Otto engine.