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You might have noticed that I have a thing for the RX-7.  Why you ask?  Something unique about the RX-7 is that it has what is known as a Wankel rotary engine.  I decided to give those of you that don't really know too much about engines a little tutorial.  This is a very rudimentary foundation of the concept of engines.

All other vehicles sold in America have piston engines.  Some have four pistons (or cylinders), six pistons, and so on.  The pistons are all arranged differently depending on the engine.  Most Hondas and Acuras have an inline four cylinder engine, which is basically four cylinders arranged, well, inline.  The same style of engine is used in many vehicles such as the Nissan Sentra, Toyota Celica, Mazda Miata, and many others.  More powerful engines have more cylinders (in general) like a V-6, which is a six-cylinder engine arranged in a "V" shape with three cylinders on each side of the "V", a V-8, or a even a V-10 (like the Dodge Viper).  Bavarian Motor Works (BMW) also produces inline six-cylinder engines as well in vehicles such as all of the 3-series (318, 323, 325, 328, M3, and so on).  I am not currently aware of any automobile manufacturers that produce inline eight cylinder engines. 

You may have noticed that all of the engines that I have mentioned have an even number of cylinders, but this does not have to be the case.   Volvo produces many five-cylinder engines, and the base Geo Metro has a 1.0 liter three-cylinder engine!  Vroom!

A special engine that is unlike the others is the horizontally-opposed engine, or boxer engine.  In all of the engines that I have mentioned, the cylinders all move in the same direction that are inline.  For example, in a basic inline four-cylinder engine, the cylinders all move in an up and down fashion with the crankshaft at the bottom of all of the cylinders.  Subaru and Porsche, however, produce boxer engines, and what they are is that the cylinders are all inline, but half of the cylinders move in the opposite direction of the other half of the cylinders.  For example, Subaru produces a boxer-four engine which has two cylinders on one side of the engine and the other two cylinders on the other side of engine, and in the middle is the crankshaft.  Porsche used a boxer-six engine in their 911s and Boxters.

Now let me just give a quick explanation of a four-stroke engine.  Automobile engines are all four stroke engines in that each cylinder goes through four "strokes" in each cycle.  In other words, the engine goes down, up, down, up in each cycle.  Each stroke has a different function, and in an automobile engine, the four strokes are intake, compression, combustion or the power stroke, and exhaust.  Other engines, such as lawnmowers and boat engines, are two-stroke, and they basically have the intake and combustion in the first stroke, and exhaust in the second stroke.

Now that bring me to the Wankel rotary engine!   The basic problem with a cylinder engine is that the pistons are all moving in a reciprocating manner where it's always changing directions.  That obviously leads to some inefficiency, and the rotary engine was produced to avoid that.  A basic rotary engine contains what are known as the rotor, which is a triangulated block, and the housing, which is in a special form known as a peritrochoid.  A peritrochoid is sort of like a fat "8".  The crankshaft runs through the middle of the rotor.   I've included a picture of the engine here: