INDIANAPOLIS, IN - Question: What has 16 cylinders, 48 valves, five camshafts and produces 1,365 horsepower?

Answer: The two GM racing engines that will propel Tony Stewart in his quest to win both the Indianapolis 500 and the Coca-Cola 600 on May 27.

Stewart will rely on two very different powerplants in his 1,100 mile racing odyssey. A 3.5-liter (214-cubic-inch) Oldsmobile IRL Aurora V8 powers the Target Chip Ganassi Racing G-Force Indy car that he will pilot at Indianapolis Motor Speedway. The Joe Gibbs Racing Home Depot Pontiac Grand Prix that he will drive at Charlotte Motor Speedway is propelled by a 358-cubic-inch GM SB2 small-block V8.

Stewart last attempted the "double" in 1999. He finished ninth in Indy and fourth in Charlotte, completing 1,090 exhausting miles.

"When I got out of the car in Charlotte in 1999, I said I was never going to do it again," said Stewart, "but the next day I had already made up my mind I was going to try it again somewhere down the road. I just didn't realize it would be this soon."

Stewart will start his fifth Indy 500 from the inside of the third row. He qualified seventh with a four-lap average of 224.248 mph, the fastest speed among the four Ganassi Racing drivers who qualified for the 33-car field.

Stewart will rely on two racing engines that have little in common except eight cylinders - and the same birthplace at GM Racing in Warren, Mich. Both motors were developed by GM engineers to meet the specific requirements of the Indy Racing Northern Light Series and the NASCAR Winston Cup Series.

The IRL Aurora V8 is based on the design of the production Aurora V8 that debuted in Oldsmobile's flagship sedan in 1994; the SB2 Winston Cup engines is a descendant of the legendary Chevrolet small-block V8 introduced in 1955. The Indy car engine's methanol fuel is metered by electronic fuel injection, while the stock car motor's four-barrel carburetor dispenses racing gasoline. The IRL Aurora V8 relies on four overhead camshafts that operate 32 titanium valves; the SB2's valvetrain employs a single block-mounted camshaft, pushrods and rocker arms to operate 16 titanium valves.

With 144 fewer cubic inches, GM's Indy car engine has 40 percent less piston displacement than its NASCAR cousin. What the IRL engine lacks in size, however, it makes up for with its higher operating speed. The IRL Aurora V8 revs to an IRL-mandated 10,700 rpm redline, while the NASCAR small-block operates under 9,000 rpm.

Despite the differences in specifications and hardware, the two engines produce very similar output. A typical stock car small-block without a restrictor plate produces 715 horsepower, approximately 10 percent more than its 650-horsepower Indy car counterpart.

An astute driver like Stewart can feel this difference in the seat of his driving suit.

"The IRL Oldsmobiles are a lot smaller than the Pontiac engines we race in Winston Cup, so they have less acceleration when I stand on the throttle," said Stewart.

The cars that Stewart will drive in Indy and Charlotte are also worlds apart. Constructed of carbon fiber and composite materials, Stewart's open-wheel Indy car weighs just 1,550 pounds. The tube-framed Grand Prix he drives in NASCAR weighs more than twice as much, tipping the scales at 3,400 pounds.

"When I compare how I drive an Indy car with how I drive a [Winston] Cup car at the Brickyard, it's like the difference between a tennis ball and a 16-pound bowling ball," said Stewart. "When you get to the end of the straight in an Indy car, you can run it wide open if it's driving right. In a Winston Cup car, you always have to lift off the throttle and get on the brakes no matter how good it's driving."