Click to enlarge pictureForza Motorsports 4 (© Turn 10 Studios)

Using the Xbox 360 Kinect body-sensing interface, players can explore the Ford GT's exterior, interior and raw specs by moving around and into the vehicle, and touching highlighted components.

Sound Effects
For some types of games, realistic audio is welcome but optional. For driving titles, every tire screech, gear shift and exhaust note is subject to intense scrutiny. Most studios find the safest option is to simply hire audio engineers who have an existing library of up-to-date automotive sounds. Most of that audio is recorded live anyway. Eutechnyx bought specific audio files for its NASCAR game, such as crowd noise from actual races, but it also incorporated engine noise from individual cars, recorded and supplied by the teams themselves.

Despite using in-car recordings, the "Gran Turismo" series has been consistently criticized for its lackluster audio, particularly when compared with the "Forza" games. This is a major sticking point for fans of these dueling franchises. And while neither Sony nor Polyphony Digital responded to requests to talk about this article, Turn 10 Studios says that it captures all of its own audio, and isolates the intake, exhaust and engine sounds from each vehicle.

Bing Images: Gran Turismo 5

What's Next?
The arms race between "Gran Turismo" and "Forza" is leaping into another dimension: "Gran Turismo 5" is one of the few games that can be viewed in 3-D, while "Forza Motorsport 4" will have limited functionality with the body-sensing Kinect control system. Kinect utilizes a 3-D camera with an integrated microphone that allows users to interact with specially designed games without using a controller or headset, using only the motion of their bodies.

Aside from differentiating these dueling franchises, both technologies have major implications for the entire racing-game genre. Stereoscopic 3-D, which generally requires glasses, can create a sense of depth that driving games desperately need. "It changes everything," Eutechnyx's Baker says. "You see the track unfold in front of you, and you start to feel the corners as you take them, as opposed to everything just being flat."

The catch, however, is capture. Creating increasingly convincing 3-D environments will require even more data and images of racetracks and vehicles. The same goes for Kinect, which Turn 10 has demonstrated as a kind of advanced ogling tool: Players can walk around their vehicles, but also explore inside, opening the car door with their hands, and craning and leaning to get a closer look at the whole interior. That means more time spent capturing and coding essentially every vehicle in the game.

The more interesting Kinect feature demonstrated so far is more subtle and less data-intensive. Never mind the phantom steering wheel you can grip and steer. In Kinect-only mode, when you lean to one side or the other, the driver's perspective edges with you, letting you peer around a blind curve or just slightly around a car before passing it.

But like the pop-out 3-D graphics in "Gran Turismo 5," the head-tracking point-of-view shift in "Forza 4" is more gimmick than breakthrough. Still, as these gimmicks stack up and evolve into new modes of play, there's potential for the next generation of driving games to be packed with more than just ever more detail and data.

"I think we're just scratching the surface," says Dan Greenawalt, game director at Turn 10 Studios. "I have the feeling that we'll all look back at these first few years of Kinect and reflect on it as a huge inflection point in interactive entertainment."

So start your engines. It's only gonna get more real from here on out.

View Pictures:  Forza Motorsports 3

Based out of the Boston area, Erik Sofge is frequent contributor to Popular Mechanics and Slate.com. He specializes in everything scientific and technical.