Why are top fuel drag race cars so long?

The length of the car has to do with straight line stability. A long, narrow car will drive straighter down the track than a short, wide car. As for the other classes, i.e. Pro Stock, Funny Car, etc. those cars are "derived" from actual street driven cars, and there are certain parameters to govern their chassis design, though they actually bear little resemblance to the original cars in their final form. These have also become elongated over the years.

At a velocity of 300 mph, or 440 feet per second, the slightest variance in the dragsters path is multiplied extremely quickly. The tires are also designed in such a way that the contact patch, where the rubber meets the track, is long and narrow. Both the length of the car and the design of the tire help to correct the straight line stability should the dragster begin to stray. Note the word "help", as these cars can and do get away from a driver very quickly when he/she makes a big enough mistake.

Contrast this with Formula 1 or Indy cars that are wider and have tires with a wide contact patch as the emphasis is more on handling and cornering.

Because with all of that hp ( about 7000) the length help keep it stable on take off. The Funny cars have the engine in front , so they don't need all that length. The pro stock, have to stay close to stock in size. They have to be a door slammer. With out the length on a top fuel the front end would go up in the air. It tries as it is even with the long rail.

To keep them from flipping backwards... same thing with motorcycles... the rear is stretched out so they dont wheely...

normally to reach the finish quicker, not to mention replacing the stock body with a lightweight aluminum.

aerodynamics