10 Banned NASCAR Modifications That Were Brilliant (and Illegal)

Learn about the creative but illegal changes made to NASCAR cars that pushed the limits of racing technology. A lot of these changes were ahead of their time, even though some of them were banned because they were unsafe or gave unfair advantages.

Tricia Quitales
April 9, 2025
4 min read

10 Banned NASCAR Modifications That Were Brilliant (and Illegal) — Diego Martinez on Pexels

Teams and engineers have always tried to get ahead in NASCAR, even breaking the rules by making creative changes to the cars. Even though some of these changes were brilliantly thought out, they were not allowed because they gave teams an unfair advantage or were dangerous. This article shows 10 of these modifications that were great but illegal. They range from changes to the car’s aerodynamics to engine tweaks that broke NASCAR’s rules. Even though they were banned, these changes showed how hard people were trying to get better, and they left their mark on the history of the sport.

1. The “Flying” Rear Spoiler

Brian on pexels

The “flying” rear spoiler used in the 1980s was one of the most well-known changes in NASCAR history. This spoiler was meant to make more downforce, improving grip at high speeds. However, it worked so well that it might have lifted a car off the ground in some situations. Even though the idea was great, it wasn’t allowed because of safety concerns.

2. The “Coke Bottle” Body Shape

Daniel on Pexels

In the late 1990s, some teams used the “Coke Bottle” shape, which narrowed the body near the back wheels to make the car more aerodynamic. This change made it easier for air to flow over the car, cutting down on drag and making it go faster on straightaways. Even though the modification worked very well, NASCAR banned it because it gave drivers an unfair advantage.

3. The “Tunnels of Air”

martin tuithof on Pexels

Some NASCAR teams tried out an idea in the 1970s called “Tunnels of Air.” The idea was to make low-pressure areas under the car to lower drag and boost downforce. This modification used smart venting systems to move air under the car, which made it faster on the track. When NASCAR discovered that the plan gave some teams a big advantage in races, it was banned.

4. The “Shark Fin”

Andrei on pexels

“Shark Fin” was a modification added to the back of the car to make it more stable by making the back bodywork longer. The idea came from studying how fish move through the water. The fin was meant to reduce drag and keep the car stable when turning quickly. Even though it worked, NASCAR quickly banned the change because of how it was made and how well it streamlined the car.

5. The “Double-Sided” Tape

Geancarlo Peruzzolo on Pexels

Even though it wasn’t a mechanical change, teams were known to change the car’s aerodynamics with “double-sided” tape in the 1990s. Teams would use tape to block off some vents so that air could flow more smoothly around the car, making it go faster. This change was taken away when it was found that teams were using it strategically to get an edge over their opponents in ways that weren’t intended.

6. The “Unrestricted Engine”

Juan Montes on pexels

In the early days of NASCAR, some teams tried out “unrestricted engines” that made engines more powerful than they had ever been. By circumventing rules meant to level the playing field, these engines were made to get as much horsepower as possible. Even though they were very powerful, these engines put the competition and driver safety at risk. They were quickly banned.

7. The “Air-Cooled Radiator”

Tom Fisk on Pexels

Some NASCAR teams tried riding with radiators that were cooled by air. The traditional water cooling system was swapped out for one that used air to keep the engine cool. This made the engine lighter and better overall. NASCAR banned it because it gave cheaters an unfair advantage and could cause cars to overheat during races.

8. The “Weight Shift” Modification

chris howard on Pexels

Many teams tried weight-shift systems in the 1980s. These involved putting adjustable weight boxes on the car to change its balance during the race. Teams could use this to make their cars more maneuverable in certain corners or on certain tracks. Even though it improved performance a lot, it was banned because it was so easy to use to gain an unfair edge.

9. The “Variable Rear Spoiler”

Auto Records on Pexels

Some teams began testing a “variable rear spoiler” in the early 2000s. This type of spoiler could change its angle during the race to make the most of downforce. This change let teams change how the car is handled dynamically, which made it more stable in straight lines and faster when turning. NASCAR banned the change because it could give some teams an edge in different race conditions.

10. The “V8 Turbocharged Engine”

Mike Bird on Pexels

Some NASCAR teams secretly tried turbocharging their V8 engines to get more horsepower and better fuel economy without breaking the rules for engines. This change made the car faster without adding the weight that comes with high-horsepower engines. After seeing how well it worked, NASCAR quickly banned the turbocharged V8 engines to keep things fair.