Start your engines! On Dec. 17, gamers in the U.S. and Europe will have the opportunity to download a new demo for the long-awaited Sony racer, Gran Turismo 5. The demo, called the Gran Turismo 5 Time Trial Challenge, will be available via the PlayStation Store.

Gran Turismo 5 Time Trial Challenge will put gamers behind the wheel of a Nissan 370Z as they test out the newly designed physics engine for GT5. Players will have the option to race either a stock version or a tuned version of the 370Z, and each version will have its own time trial events on the same track.

Sony has also announced a contest that will begin adjacent to the release of the demo, and the Grand Prize will go to the player with the fastest combined time on both the challenges. The Grand Prize will be airfare, hotel accommodations and entrance to the Indy 500 on May 30, 2010, as well as two all-access passes for Carb Day. [Whatever that is; click the link to the official Sony blog below for more info.] Five runner-ups will get a voucher to download Gran Turismo for PSP. The contest begins on the day the demo releases, and ends Jan. 25, 2010.

Get more info straight from the horse's mouth, at the official SCEA website.