Photo credit: edvvc from London, UK Taken on: July 7, 2001 License: Creative Commons Attribution 2.0
Photo credit: edvvc from London, UK
Taken on: July 7, 2001
License: Creative Commons Attribution 2.0
At a time when the Lotus 79 seemed unstoppable, Brabham responded with the BT46B, introduced mid-season at the Swedish Grand Prix.
In the first few races, the Brabham was not an uncompetitive car, but Lotus was clearly the team to beat. When the BT46B arrived, it won its debut race at the Swedish Grand Prix. But how was it built, was it developed in secret, how did it actually work, and why did the team decide to withdraw it?
Who Built the BT46B Fan Car
The BT46B was the brainchild of Gordon Murray, Brabham’s young and fiercely inventive chief designer.
However, Murray was already known for thinking laterally, often questioning assumptions other designers look for granted.
At Brabham, he worked under team owner Bernie Ecclestone, a man who understood that F1 was as much about power and influence as lap time.
The base car, the Brabham BT46, was designed around the wide and heavy Alfa Romeo flat-12 engine.
That engine caused serious packaging problems and compromised aerodynamics, especially compared to the sleek Lotus 79 that was dominating 1978 through ground-effect tunnels.
So what was the solution? Murray did not try to copy Lotus directly. Instead, he went hunting for something better.
And the result was not an evolution of ground effect; it was a bypass around it.
Was the Car a Secret
Yes, and deliberately so. Development of the fan car happened away from curious eyes, with private testing.
The fan of BT46B itself was visually obvious, so Brabham went to unusual lengths to hide it whenever possible.
At the 1978 Swedish Grand Prix, in the middle of the season, mechanics famously covered the rear fan with what looked like dustbin lids when the car was parked.
However, the rivals’ immediate reaction was one of suspicion and concern, wondering what this car was and how it actually worked.
The engineers knew something unusual was happening, but they did not yet understand how devastating it would be.
Niki Lauda and John Watson were instructed to sandbag in qualifying, intentionally holding back to avoid revealing the car’s true pace. In hindsight, that instruction alone tells you how confident Brabham already was.
How the BT46B Actually Worked
The heart of the BT46B was the large fan mounted at the rear of the car. Unlike later banned devices, this fan was mechanically driven by the engine through a system of clutches. Its primary function, at least on paper, was cooling.
The fan sucked air from underneath the car, while flexible skirts sealed the sides of the floor against the track surface. This created an intense low-pressure area under the chassis, effectively gluing the car to the asphalt. The key difference compared to the Lotus 79 was consistency. Ground-effect tunnels needed speed to work properly. The Brabham did not.
At low speed, under braking, and even mid-corner, the car produced massive downforce instantly. Drivers did not need to wait for airflow to build. Grip was simply there, all the time.
Gordon Murray exploited a loophole in the regulations by mounting a horizontal radiator above the engine. He demonstrated that more than half of the air moved by the fan was used for cooling. Aerodynamic downforce, therefore, was classified as a secondary effect. According to the wording of the rules in 1978, the car was legal.
Technically, it was brilliant. Philosophically, it was dangerous for everyone else.
The One Race That Changed Everything
At the Swedish GP, the BT46B did not just win. It embarrassed the field.
Niki Lauda pulled away with ease and won by over half a minute.
What made the result even more unsettling was Lauda’s later admission that he was not pushing anywhere near the limit.
From an observer’s perspective, the car looked calm and planted while others slid and struggled.
Why Brabham Removed It
Officially, the car was declared legal by the governing body of the time.
Rivals pressure was immediate and intense, Colin Chapman of Lotus, protested fiercely.
Claims were made about debris being thrown from the fan car, about safety risks, and about the spirit of the regulations being violated.
However, the debate is even now about whether those safety claims held real weight. Gordon Murray has always argued that the fan rotated too slowly to fire stones dangerously, but in F1, perception can matter more than physics.
Ecclestone voluntarily withdrew the car before the next race in France to appease his rivals, following protests from other teams.
👉 Colin Chapman’s Greatest “What-If”: The Story of the Banned Lotus 88
👉 The Lotus 72: How Chapman Built a Car That Couldn’t Be Stopped
Would It Have Won the Championship
In my opinion, yes, assuming reasonable reliability.
The evidence points strongly in that direction; Lauda and Murray both believed the car was vastly superior to anything else on the grid, and even the drivers were told not to push.
However, the BT46 Solved the biggest weakness of ground effect by making downforce independent of speed.
The only real question mark was durability, the standard BT46 struggled badly with reliability in 1978, and the fan system added complexity.
Over a full season, failures were likely, but even with occasional retirements, the performance margin looked large enough to overcome that.
After the fan car disappeared, Lotus cruised to both championships. Brabham still finished third overall using the compromised standard car. That alone hints at what might have been.
How Much Faster Could the Brabham BT46B Have Been?
At the Swedish GP, the Brabham’s potential advantage over the Lotus 79 was staggering, with estimates suggesting it could lap 1 to 1.5 seconds faster per lap.
Official times from qualifying and the race showed a much smaller gap, but this was by design, Lauda and Watson deliberately sandbagged to hide the car’s true pace.
John Watson and Niki Lauda in qualifying, were less than a second off Mario Andretti’s pole time.
But during the race, Niki Lauda admitted he was only using about 70% of the car’s potential.
The Brabham BT46B remains the only Formula One car with a perfect win record. One race, one victory, zero defeats. More importantly, it stands as a reminder that Formula One’s limits are not always technical. Sometimes, the real boundary is how much disruption the sport is willing to tolerate.
The fan car did not just challenge Lotus. It challenged the balance of power itself. And that, more than lap time, is why it was never allowed to race again.
