In NASCAR, as in any other type of motorsport series, the engine is perhaps the most important part of the car, and certainly the most expensive piece of equipment in the sport. It is impossible to be successful with a bad engine, which makes teams and manufacturers spend lots of time and money into research to develop the best engines possible. In NASCAR's Cup Series, its premier racing car series, there are 3 different engine suppliers today: Toyota, Chevrolet, and Ford. With 3 different engine suppliers, you can already tell that engines are not all the same. However, they are all quite similar, given that they have to follow the same set of rules.
All three of the engine manufacturers are also big road car manufacturers. Their interests in being in NASCAR are related to their own commercial need of selling cars. Toyota, Chevrolet, and Ford all use NASCAR as a place to develop and showcase innovations that may be implemented into their road cars, bought by their customers. Also, NASCAR is a way to do some marketing and expand their brand, especially when there is some competition involved. If all engines were exactly the same, there would be no reason for all three companies to be involved in NASCAR, and the sport would suffer financially.
At the same time, NASCAR does not want a single manufacturer to be extremely dominant. Therefore, they must limit how different engines can be from each other to ensure that there is still competition in the sport. In fact, the Manufacturer's Championship is a big part of the NASCAR season with Toyota, Chevrolet, and Ford competing to take the trophy home every year.
The way NASCAR ensures there is a fan attracting competition is by creating regulations that must be followed by teams, which change from time to time. These levels of changes are called generations.
NASCAR cars come in generations. That is, all cars must follow the same specs and regulations, which eventually evolve and change into a new generation. Currently, NASCAR cars are what is called the Generation 6 cars, which debuted in 2013. The Gen-6 cars are due to be retired soon, with a next generation of more modern, and most importantly different cars to come.
The specs that Toyota, Ford and Chevrolet must follow when designing their NASCAR engines is likely to change soon, following new technologies and the new rules established by NASCAR. Naturally, the three engine suppliers are part of the discussion in developing the next generation of NASCAR cars, and their engines.
Although the specifics of engine rules won't change greatly for the next generation, the expectation is that the engine will have more electric components than the current version, that is, there will be hybrid engines. Hybrid engines are those that are powered by a combination of both fossil fuels like gas and electric energy. Notably, all three engine suppliers have been investing in extensive research into electrical engines the last few years, and sell cars with hybrid engines. Toyota, Ford and Chevrolet would all be making engines for NASCAR that are more similar to what they sell to their customers, and to what the future of cars look like.
The shift to hybrid changes has been happening in other motorsport categories as well, with Formula 1 having hybrid engines since 2013, and Indy car planning a similar shift. The change also makes sense from an environmental perspective; hybrid engines are more environmentally friendly, as they pollute less. Making less damage to the environment is crucial for NASCAR's (and all of motorsport's) long run success, which also helps explain the transition to hybrid engines.
In addition, adding a hybrid engine to the sport might even attract more car manufacturers, who are looking to showcase their own work in hybrid and electric technology. The addition of new known car companies that supply engines would increase competitiveness, something that is always good for the sport and fun for the fans.
While the engine itself will change, the competition between the three companies that supply them to NASCAR won't. Engines will still all have to follow the same rules, but will not be all the same, as Ford, Toyota and Chevrolet will each design their own NASCAR hybrid engines and supply to the teams that use them.