You probably won’t give much thought to which engine to choose in your next car. If you’re like most people, you care more about the car’s color than you do about its cylinder configuration.

But, really, what’s a car without an engine? Just some upholstery on wheels. Nowadays, with more option packages and trim levels available than ever before, you have more engine choices in a particular model. And your choice can affect the price, performance and long-term ownership cost of your new vehicle.

The ABCs of Shape

Today’s engines come in three basic shapes. The in-line configuration, or I, places the cylinders side by side in a neat row. In the V design, the cylinders are grouped in two slanted rows, forming the letter V. In a horizontally opposed (HO) design, the cylinders are arranged in two flat groups on either side of the engine. Because the cylinders on one side lie in the same horizontal plane as those on the other side, this design is sometimes called a “pancake.” And, because the moving pistons seem to punch at one another like two prizefighters standing toe-to-toe, it’s also sometimes called a “boxer.”

The long, narrow shape of the I (when turned sideways) allows for a shorter hood. The V is a more compact design for larger engines. The HO design reduces engine height and lowers the center of gravity, which often improves cornering.

While gearheads may argue endlessly about the merits of one design over another, Jim MacPherson, an editor of the AAA Auto Guide for 2003, says, “The vast majority of shoppers should concern themselves more with how a car performs, not with what the manufacturer did to achieve that performance. Is it quiet enough? Do you have adequate acceleration from a stop? Adequate power for passing and merging? Those are the important qualities.”

Technology Triumphs

Advanced technology and engineering have made most of the enthusiasts’ old arguments obsolete. “Innovations such as active engine mounts and counter-rotating balance shafts have quelled most problems with noise, vibration and harshness once associated with certain engine configurations,” says MacPherson. “Even the old rules—such as the one associating any four-cylinder engine over 2 liters with excessive noise and harshness—don’t really apply anymore.”

Configuration counts in one important respect, however: accessibility. How the engine fits in among all the other stuff crammed under the hood can make routine maintenance either relatively easy or extremely difficult. On some models, for instance, the transverse-mounted V-6 fits so snugly that the spark plugs in the back row seem almost impossible to change. That matters even if you don’t change your own plugs, because the fit and configuration may make an ordinary task more labor-intensive—and therefore more expensive.

Visit the dealer’s service department before you buy and ask for a schedule of required maintenance (with prices) for the model you’re looking at.

Power Principles

Often, engine size distinguishes one trim level from another within a particular model line. Size is measured in displacement—the total volume (in liters) occupied by all the pistons as they move. Generally, larger-displacement engines generate more power for accelerating, towing and hill climbing. But they also use more gas.

Other than increasing displacement, carmakers can also boost engine power by finding better ways to expel exhaust, by using more sophisticated valve systems, or by pumping more air in the combustion chambers. To add more air, engineers usually use either a turbocharger (a pump driven by exhaust gases) or a supercharger (a pump driven by a belt connected to the engine itself).

Of the two, turbochargers tend to be more finicky. Although their performance and reliability have improved dramatically in newer designs, “turbos definitely raise some potential service issues,” notes MacPherson. “For one thing, you have to be especially scrupulous about observing the recommended oil-change intervals.” For another thing, a turbo makes certain bad behind-the-wheel habits more expensive. “When you’re late for an appointment, you can’t rocket into a parking space and then turn off the engine immediately,” says MacPherson. “You force the turbo to spin way up and then shut off its oil supply. Of course, that increases wear and eventually leads to bigger repair bills.” On the plus side, turbos provide a nice boost for passing or merging without seriously reducing your overall fuel economy.

Carmakers can increase an engine’s power without increasing its size by engineering more valves per cylinder. These “multi-valve” engines deliver more oomph as rpms climb. Or engineers can squeeze more power out of smaller engines with variable valve timing systems, such as those popularized by Honda and BMW.

“It’s fair to say that the more complex the system, the more expensive it is to repair when it breaks,” says MacPherson. “If you do need a valve job on a multi-valve engine, there are more parts to machine—which means more labor and bigger bills.”

At the end of the day, an engine is just another part of a car. Engineers consider an engine’s weight, power and shape when fitting it into an overall design. As a consumer, you have to judge the “fit” of an engine the same way you judge the fit of a new pair of shoes—by feel. Does it give you enough power to haul what you need to haul? Does it give you enough pick-up to merge from an exit ramp? To pass at 55? If the answers are yes, then you’ve got a good fit—no matter what the shape.