Oh my... there are many types of engines available. I'll try to answer this one relatively completely. There are rotary engines (certain Mazdas) and piston engines (everything else). Piston engines are available in many different cylinder layouts and with different valvetrains and methods of fuel delivery. Or for that matter, different fuels, like diesel. CYLINDER LAYOUT: Inline engines, with all of the cylinders in a single line, need only one cylinder head and valvetrain, which reduces the part count somewhat. They are simpler to put intake and exhaust manifolds on. However, they do get long. FWD cars mount their engines transversely, so they are generally limited to 4 cylinders if they use an inline engine. RWD and AWD cars can use 6 cylinders before the hood gets ridiculously long. V-engines have two banks of cylinders, and thus require two cylinder heads, two valvetrains, and (generally) two exhaust manifolds. Compared to an inline engine, you can get twice as many cylinders in (roughly) the same length. Volkwagen takes it a step further by setting the cylinders in each bank in a zig-zag; their W-8 is about the same length as a conventional V-6! Horizontally-opposed ("Flat' or "Boxer") engines, used in Subarus and Porsches, are similar to V-engines except that instead the banks being separated by either 72 or 90 degrees (the most common), they are 180 degrees apart. This results in a lower center of gravity, which helps handling. However, they are relatively wide, and it's EXPENSIVE to get a new exhaust manifold for them. VALVETRAIN: Pushrods, as used in old, American V-8s, are still available in a couple of American muscle cars, but I have no idea why. IMAO, pushrods are for those who believed time stopped fifty years ago. Most modern engines are overhead-cam designs, either single-cam (SOHC) or twin/dual-cam (DOHC). SOHC engines have two valves per cylinder; 1 intake and 1 exhaust. This limits the breathing ability of the engine, and thus limits horsepower. But for non-competitive uses, like commuting or as a family car they are quite servicable and more economical than a DOHC engine. DOHC engines have four valves per cylinder; 2 intake and 2 exhaust. This allow more airflow through the engine, thus increasing power. That is why most modern sports cars (or sport-trim econoboxes) use twin-cam engines. FUEL DELIVERY: Carbeurators are the ancient way to deliver fuel to an engine. IMAO, the only use for them is to fit within the rules of those motorsports so archaic as to disavow any advances in engine technology in the last fifty years (NASCAR), or for applications where simplicity is more important than either performance or economy (lawn/yardcare equipment). Throttle Body Injection (TBI) is a little better than carbs, but not by much. It DOES allow better control and a greatrer ability to adjust for varying conditions (throttle position, temperature, humidity, etc). However, given where the injectors are in the intake tract, they have many of the drawbacks of carbs. Multi-port fuel injection injects the fuel right before the air gets drawn through the intake valve into the cylinder. Much more efficient; more power from less fuel. Direct injection injects the fuel directly into the cylinder just before ignition, allowing even more efficiency than MPFI. AFAIK, direct injection is just emerging in gasoline engines. THE LOWDOWN: Any modern car, performance or otherwise, will be fuel-injected, either multi-port or (less likely) direct injection. MPFI is well proven to be the best for both economy and power, though direct injection may replace it in a few years. It will also have overhead cams. For general use, a SOHC inline-4 is the cheapest, simplest, most economical choice. That is why SOHC I-4s are probably the most common engine in use today. Beyond that, it's personal preference. Personally, I'd like to replace the SOHC Inline-4 in my car with a DOHC flat-6, but they don't make one that'd fit my car. Clarification - (4-11-06) - IMAO = In My Arrogant Opinion. Uncommon except in places normally occupied by egotistical people ;)