While every car racing within NASCAR must abide by the strict regulations set forth, there can be just the slightest variation and differences between different NASCAR models. When people began stock-racing back in the 1940s, drivers would purchase cars directly from dealerships with no modifications on them. Drivers would use the same cars that people at home were driving. In 1947, NASCAR was formed and since early racing tracks were primarily dirt, the organization allowed for vehicle modifications for durability.
Over the years, more and more modifications have been allowed slowly increasing the performance of the cars over the years. The only real variation of NASCAR models today is in their engines and body shell. The overall shape of each of the cars, the tires, suspensions, fueling systems, electronics, and transmission are all the exact same.
There are currently three different manufacturers who produce NASCAR cars: Toyota, Ford, and Chevrolet. Each of these companies is required to submit their engine design to NASCAR for approval. NASCAR only allows these parts for competition:
Racing teams are able to reuse these parts and some elements are allowed variation. For example, the block and cylinder heads of the engine can be remachined within a range of certain tolerances. The tolerances for piston ring gaps and bearings are the only pieces that engineers did not have to follow any NASCAR regulations on. In terms of quantitative regulations for the engine, all engines have to feature a 358 cubic inch (5.86 liter) pushrod v8 capacity that develops 750 horsepower. This standard was set in place as a standard and limit for all NASCAR cars. The current regulations on horsepower for NASCAR is 750 hp on tracks shorter than one mile and just 550 hp on tracks longer than 1 mile. Overall, due to the strict regulations that NASCAR has set in place, all engines will have almost the exact same performance, with a variation of about 1-2%.
NASCAR prohibits the use of turbocharged engines and no car has ever used one in the history of the sport. This is largely due to turbo lag which can result in the engine delivering instant power likely leading to an error or crash.
NASCAR uses a template which it refers to as the Gen-6 Racecar to establish a level playing field for all drivers and car models. The whole concept behind the template is to ensure that all drivers are racing under the same conditions. The template is made up of the chassis (the underpinnings of the racecar) with steel tube welding to complete the skeleton of the car. Teams will then drop their own distinctive body shell on the skeleton giving the cars their different appearance, but still having the same shape. All race cars looking to race in NASCAR must meet and be approved by the guidelines set by this template.
In the sport of NASCAR there are many different locations where racing events are held and because of this there are many different tracks a driver would race on. Teams may want to use different cars depending on the track and which one optimizes their performance. Short tracks will favor cars where top speeds are lower and turning is tighter, while cars with higher speeds would be used for longer tracks. The short track cars are designed with as much downforce as possible to increase friction and the ability of the car to stick through a tight or sharp turn. This higher downforce however does increase air resistance which is why these cars are only used on short tracks.
Super Speedway tracks such as Talladega and Daytona are examples of longer tracks and where you would want to be racing higher speed cars with less air resistance. In the early days of racing, teams had the ability to use three or four different cars, however as of 2020 NASCAR has limited that number to just two.
Before any car can race in a NASCAR event it must first be inspected and approved by a NASCAR official. These inspections take place on race days a couple hours prior to the start. Inspectors carefully examine each car and make sure the wing follows regulations and that tolerances fall within a certain range. Teams often bring mallets and tools to this part of the inspection process in case they need to make any additional adjustments. The cars are also inspected after the race a final time to double check that no regulations or rules have been violated.
If the car fails NASCAR's inspection it will not be allowed to race and depending on the infractions could be subject to penalties as well. An example of this was in 2007 when NASCAR found that Jeff Gordon's #24 car had modified their fenders in an area in which the NASCAR template could not detect. As a punishment the car was impounded until the fenders were fixed, the team was fined $100,000, and got a 100 point penalty as well, an extremely costly mistake.
All NASCAR race cars are built with power steering to both help the drivers steer the vehicle when traveling over 200 mph and to keep accuracy on the track. These power steering systems are what controls the way in which the wheels are turned. This allows drivers to yank the wheel rapidly in a certain direction and not spin the car out of control.
All NASCARs are designed and built to be able to go in reverse due to safety reasons in case the driver ever needs to change directions. NASCARs currently have a 4-speed manual transmission known as a "H" pattern, so sometimes it is mistaken that they are not able to go in reverse. The reverse gear is also used when unloading/loading the vehicle.