The original races were run on dirt tracks that got rutted and bumpy. The unmodified cars were not tough enough for this type of abuse, so NASCAR began allowing modifications to the stock cars to increase their durability. Over the years, more and more modifications were made, sometimes to increase safety (see How NASCAR Safety Works for details) and sometimes to improve competition. NASCAR strictly controls all of these modifications, which are spelled out in detail in the NASCAR rule book. Cars are checked for compliance with these rules at every race.
Today, NASCAR race cars have very little in common with street cars. Almost every detail of a NASCAR car is handmade. The bodies are built from flat sheet metal, the engines are assembled from a bare block and the frame is constructed from steel tubing.
Here we'll see how these race cars are made, starting with a component that is key to the drivers' safety and provides the foundation for everything on the car: the frame. The Frame
The frame consists of a structure of round and square steel tubing of varying thickness. The bulk of the structure surrounds the driver. This part of the frame -- the roll cage -- is made of the thickest tubing and is designed to stay together, protecting the driver during any type of crash The Engine
The engine in the NASCAR race car is probably the most crucial component. It has to make huge amounts of power for hours on end, without any failures.
You might think that these NASCAR engines have nothing in common with the engine in your car. What we learned was a little surprising: These engines actually share many features with street-car engines.
Dodge provides the engine block and cylinder head for the engines used by Bill Davis Racing. They are based on a 340-cubic-inch (5.57-liter) V-8 engine design that was produced in the 1960s.
The actual engine blocks and heads are not made from the original tooling. They are custom-made race-engine blocks, but they do have some things in common with the original engines. They have the same cylinder bore centerlines, the same number of cylinders and they start out at the same size (they get a little bigger during the building process). Like the original 1960s engines, the valves are driven by pushrods
The engines in today's NASCAR race cars produce upward of 750 horsepower, and they do it without turbochargers, superchargers or particularly exotic components. How do they make all that power?
Here are some of the factors:
The engine is large -- 358 cubic inches (5.87 L). Not many street-cars have engines this big, and the ones that do usually generate well over 300 hp.
NASCAR engines have extremely radical cam profiles that open the intake valves much earlier and keep them open longer than in streetcar engines. This allows more air to be packed into the cylinders, especially at high speeds.
The intake and exhaust are tuned and tested to provide a boost at certain engine speeds. They are also designed to have very low restriction -- that is, to provide little resistance to the gases flowing down the pipe. There are no mufflers or catalytic converters to slow the exhaust down, either.
They have carburetors that can let in huge volumes of air and fuel -- there are no fuel injectors on these engines.
They have high-intensity, programmable ignition systems that allow the spark timing to be customized to provide the most possible power.
All of the subsystems, like coolant pumps, oil pumps, steering pumps and alternators, are designed to run at sustained high speeds and temperatures.
When these engines are machined and assembled, very tight tolerances are used (parts are made more accurately) so that everything fits perfectly. When an engine (or any part, for that matter) is designed, the intended dimensions of the part are given along with the allowable error in those dimensions. Making the allowable error small -- tightening the tolerances -- helps the engine achieve its maximum potential power and also helps reduce wear. If parts are too big or too small, power can be lost due to extra friction or to pressure leakage through bigger than necessary gaps.
Several tests and inspections are run on the engine after it is assembled:
It is run on the dynamometer (which measures engine power output) for 30 minutes to break it in. The engine is then inspected. The filters are checked for excess metal shavings to make sure no abnormal wear has taken place.
If it passes that test, it goes back on the dynamometer for another two hours. During this test, the ignition timing is dialed in to maximize power, and the engine is cycled through various speed and power ranges.
After this test, the engine is inspected thoroughly. The valve train is pulled and the camshaft and valve lifters are inspected. The insides of the cylinders are examined for abnormal wear. The cylinders are pressurized and the rate of leakdown is measured to see how well the pistons and seals hold the pressure. All of the lines and hoses are checked.
Only after all of these tests and inspections are finished is the engine ready to go to the races. Insuring the reliability of the engine is critical -- almost any engine failure during a race eliminates the chance of winning. Tyres
Tires are another critical component on the race car. A high-speed blowout can be incredibly dangerous.
Like the tires on your car, NASCAR tires are radial tires, but that is about the only similarity. The tires on a NASCAR race car have some very special requirements. They have to remain stable at very high temperatures and speeds, provide incredible traction and be changed very quickly.
Nitrogen Instead of Air
Most of the teams remove the air from the tires and replace it with nitrogen. Compressed nitrogen contains less moisture than compressed air. When the tire heats up, moisture in the tire vaporizes and expands, causing the pressure inside the tire to increase. Even small changes in tire pressure can noticeably affect the handling of the car. By using nitrogen instead of air, the teams have more control over how much the pressure will increase when the tires heat up.
Inner and Outer Tires
On tracks that are more than 1 mile (1.6 km) long, where speeds are faster, NASCAR rules require that tires contain an inner liner. This is essentially a second tire mounted inside the first tire. It mounts to the rim and has its own separate air supply. If the outer tire blows, the inner tire is still intact, allowing the driver to bring the car to a controlled stop.
Different Compounds for Different Tracks
NASCAR regulates which tire compounds are used on each track. The tire compound is the material the tire is made from -- a softer compound can provide more grip but wears faster, while a harder compound will last longer. Each track causes tires to wear differently, and the inside tires wear differently than the outside tires. Track surface, number of turns, tightness of turns and type of banking are all factors that determine how a tire will wear. Since tires are so critical for safety, NASCAR and Goodyear have determined the best compounds for the inside and outside tires for each track, and these are the tire compounds that the teams are required to use.
NASCAR tires look completely bald, but that's not because they are worn out. It is by design. On a dry track, tires can generate more traction if more of their sticky rubber is in contact with the ground. Putting a tread pattern on the tire helps in wet weather, but in dry weather it is better to have the whole tire touching the ground. That's why NASCAR races stop whenever the track is wet.
How do they get the tires on and off so fast?
You may have seen a NASCAR pit stop before. In 12 to 14 seconds, seven people manage to completely refuel the car and change all four tires. This requires incredible hand-eye coordination, but there are a couple of tricks the teams use to make things a little easier. When the new tire is placed onto the car, the five lug nuts are already attached to the wheel by an adhesive. The studs are long and have no threads for the first three-quarters of an inch. This ensures that the lug nuts do not get cross-threaded, making it easier for the tire to be positioned.