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In some of our past and upcoming articles, we've been throwing around the word homologation, and it occurs that we should pause to explain what it means.

The etymology of the word is Greek; "homologate" is derived from homologeo, Greek for "to agree." It means the granting of official approval after demonstrating adherence to a set of regulations or requirements. In an automotive context, it usually refers to racing.

Homologating a car for racing means obtaining approval from the officiating body to enter a car in a specific  racing class or category. Homologation rules vary depending on the form of racing, and they often change from year to year. They generally include things like engine displacement, wheelbase, minimum weight, production quantity, and allowable modifications. For example, a particular class might require that all entrants be production cars, with engines between 1.6 and 2.0 liters.

Homologation is not the same as qualification. Most racing organizations require that each car undergo technical inspection to confirm that it conforms to the rules -- racing teams have a tendency to bend the rules as far as they can (i.e., cheat). It's entirely possible for a car to be homologated and still be technically disqualified. A Mazda MX-5 (Miata), for example, might meet the homologation requirements for the hypothetical class described above, but if you show up to a race with a Miata powred by a 5.0 L Ford V8, the inspectors will still disqualify you.

The biggest issue in racing homologation is typically the production requirements. Racing officials prefer to keep production cars separate from one-offs or prototypes, so as to maintain a more level playing field -- naturally, matching a purpose-built race car against a stock street car is not going to make for fair competition. The problem is trying to decide what qualifies something as a production car. Homologation rules usually set a requirement for minimum annual production; it might be 5,000 cars, or it might be 500. The production cars rarely have to be identical to the racers, but if the racers are to use certain configurations or components, the stock cars usually have to, as well. For example, if the racer is going to have an intercooled, turbocharged engine, the production cars must also have turbochargers and intercoolers. The rules might allow the racer to remove emissions control equipment, run higher boost pressure, and use different camshaft and ignition timing, but require that the racing engines use the same basic engine block and heads as the stock car.

The intricacies of homologation have led to the creation of various interesting limited-production cars known as "homologation specials." An homologation special is a car offered for public sale to ensure that some equipment or specification needed for racing is sold in sufficient quantities to meet homologation requirements. Homologation specials are usually rare, expensive, and not necessarily well suited to normal driving, but they have a tendency to become coveted collector's items. Famous examples include the Dodge Charger Daytona and its Plymouth Road Runner Superbird cousin; the fearsome Porsche 959; and the original BMW M3.

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One of the most confusing (and frequently contentious) questions in the automotive realm is the difference between horsepower and torque. You may have heard any number of pithy expressions, like "horsepower sells cars, but torque wins races," or fans of big-engine muscle cars complaining that 200-horsepower four-cylinder engines are "gutless." Surprisingly few of the worthies who throw around comments like that, though, are actually able to define the difference. What IS the difference between horsepower and torque, and what effect do they have on how a car performs?