In 1977, French manufacturer Renault surprised the conservative world of Formula One by exploiting a long forgotten loophole in the sport's engine regulations. Eleven years earlier, the FIA had abandoned the unpopular 1.5L formula in favor of a 3.0L limit, in a bid to help the cars of the day outrun the increasingly more powerful large capacity GT cars.

However, the new regulations also contained a clause allowing the use of 1.5L forced induction engines, something which was quickly forgotten after the resounding success of the legendary Cosworth DFV V8. Renault had remembered though, and decided to build the Renault-Gordini EF1, an innovative 90 degree V6 incorporating a large exhaust-driven turbocharger.

The EF1: a major breakthrough in F1 technology. The EF1: a major breakthrough in F1 technology.

Although the engine was still a highly experimental affair, and Renault's lack of experience in Formula One chassis design left the RS01 nothing more than a racing testbed, it didn't take long for the French squad to become a major threat to the establishment.

After two seasons of meticulous development, their competitor's laughs over the comically steaming "Yellow Teapot" stifled, and the worrying began. Driver/engineer Jean Pierre Jabouille managed to take the first ever win for a turbocharged car with the new twin-turbo RS10 at the 1979 French Grand Prix at Dijon, with teammate Rene Arnoux third after an awe-inspiring battle with Ferrari's Gilles Villeneuve.

Villeneuve vs Arnoux, a battle for the ages. Villeneuve vs Arnoux, a battle for the ages.

Though Gilles had managed to beat Arnoux's turbo weapon, and Ferrari secured both titles with Jody Scheckter, the writing was on the wall. Renault's was only just becoming reliable enough to consistently challenge for race wins, and their engine was already powerful enough to reel in anything on the straights.

There was no telling how much faster they could become. Clearly, the naturally aspirated engine was on the way out of Formula One, as the turbo became stronger and stronger. Not content with sitting on their laurels enjoying their recent success, Ferrari's top engineers started work on a forced induction engine of their own.

Ironically, the Scuderia had started their F1 career with a forced induction engine, as they followed Alfa Romeo into the 1.5L supercharged category with 1948's V12-powered 125 F1. After some thirty years of trusting in less complicated and generally more reliable naturally aspirated designs, the scarlet squad finally returned to its roots.

The Comprex pressure wave supercharger. The Comprex pressure wave supercharger.

Despite the success of the Renault concept, Ferrari elected to try an entirely different solution in the quest for power. The biggest problem with turbo engines was the phenomenon known as lag. As the turbine was driven by the exhaust gases, it wouldn't actually function until a certain pressure was reached.

This caused the engine to become stagnant for a few seconds, before experiencing a sudden surge of power as the turbo kicked in. This lack of responsiveness severely hampered the car on low-speed circuits full of tight turns, and the sudden power surges negatively affected drivability. The unpredictable on/off performance could drastically upset the car's balance, and surprise the driver into making a mistake.

Cutaway of a Comprex supercharger. Cutaway of a Comprex supercharger.

Keeping these concerns in mind, Ferrari's engineers sought a way to combine the responsiveness of a mechanical belt-driven supercharger, and the potential power of an exhaust-driven turbine. As it happened, a novel technology had just been developed by Swiss engineering firm Brown Boveri, the Comprex.

This system, utilized a cylindrical cell rotor driven by a belt, similar to the Roots-principle in a traditional supercharger. However, the cell rotor also utilized the pressure waves generated by the exhaust. Individual cells within the rotor alternately closed and open the intake and exhaust side of the supercharger as it rotates.

Fresh air was first drawn into the cell rotor, which then closed off the intake. Once the fresh air was contained, pressurized exhaust gas was let in, which helped compress the fresh air present within the rotor. The newly compressed air was then released into the engine through a secondary passage at the "top" of the rotor, after which the intake side closed and an exhaust passage opened to let the exhaust gases out again. As the exhaust was expelled, the change in pressure would suck in more intake air, and the cycle would start anew.

As both motive power from the engine and the pulses from the exhaust contributed to the compression process, the system effectively combined the best of both worlds. The belt ensured instant response from idle, while the pressure waves helped reduce the power loss normally associated with an engine-driven supercharger.

The 021 V6 fitted with the Comprex system. The 021 V6 fitted with the Comprex system.

Though the Comprex seemed very promising, famous engineer Mauro Forghieri and designer Antonio Tomaine weren't keen on taking any chances. Along with the Comprex, the team developed a twin Kuhnle, Kopp und Kausch turbo version of the new engine, the 120 degree 021 1.5L V6.

Aside from the need to achieve higher power figures in order to challenge Renault, the motivation for the switch to a smaller engine was the need for more efficient packaging. was The 312T-series used from 1975 up to 1980 had used an at the time very powerful 180 degree V12 (or flat-12) engine, which in turn dated as far back as 1970's 312B.

This was an excellent concept with a very low center of gravity, but as Formula One focused on ground effect after dominance of the Lotus 79 in 1978, the big twelve quickly became obsolete. With its cylinder heads directly blocking the path of a potential venturi tunnel, a crucial part of generating meaningful ground effect, it was something of a miracle the hastily adapted 312T4 was even remotely able to take the crown in 1979.

Similar to the V12 used in the 1960's 312 series, the V6's cylinder heads had an inverted layout, with the exhaust within the V of the engine, and the intakes on the outside. The wide angle provided space for such a layout, while at the same time being narrow enough to avoid getting in the way of the venturi tunnels crucial to developing the coveted ground effect. The inverted cylinder heads also helped facilitate this, as they eliminated the need for large exhaust pipes on either side of the engine.

During initial testing at Ferrari's Fiorano test track, drivers Gilles Villeneuve and Didier Pironi were impressed by the performance of the Comprex version. Pironi in particular praised its responsiveness and drivability, and likened it to a naturally aspirated engine that simply happened to have a lot of extra power.

Although Ferrari never officially released performance figures for the exotic engine, Pironi's comments suggest a number higher than the 312T5's 515 horsepower, while falling behind the savage twin turbo variant capable of pushing out around 600 horsepower in qualifying trim, and 540 for the races proper.

When you push on this one, it seems to have a powerful naturally aspirated engine. You don't feel the turbocharging, it seems like a naturally aspirated engine with a lot of horsepower. Didier Pironi.

Gilles Villeneuve testing the Comprex car at Fiorano, 1980. Gilles Villeneuve testing the Comprex car at Fiorano, 1980.

Due to the positive feedback coming from the Scuderia's driving team, a single chassis fitted with the Comprex system was sent to the first Grand Prix of the 1981 season, the United States Grand Prix West held on the sunny streets of Long Beach, California.

Initially, the car had been named 126BBC (Brown-Boveri Comprex), reflecting the origin of the innovative forced induction system. Before its debut in practice at Long Beach however, the name was changed to 126CX to bring it in line with its twin turbo brother, the 126CK, which was named after turbo manufacturer KKK.

Villeneuve blasting through the streets of Long Beach in the 126CX. Villeneuve blasting through the streets of Long Beach in the 126CX.

On the tight and twisty street circuit, the 126CX was thought to have the advantage over its more powerful sibling. While the 126CK was far more powerful, the turbos would have a hard time keeping up to speed out of the slow and technical corners that made up the Californian track.

Gilles Villeneuve was given the honor of taking the car out in practice. Sadly, he didn't get very far. Though the 126CX performed reasonably well, a snapped supercharger belt ended its run prematurely. Since there were no spares at hand, and nor real incentive to continue using the slower setup, the car was sidelined in favor of a second 126CK chassis.

The unsuccessful run stifled Ferrari's interest in the 126CX, and the drivers' preferences were duly overruled. From that point on the Scuderia would build its efforts around the more conventional 126CK, despite its unruly temperament and detrimental effect on the already lackluster 126C chassis' balance.

Ferrari engineer Nicola Materazzi had already drawn up a rough draft of a new configuration using two smaller Comprex cell rotors driven through a hydraulic clutch system instead of a belt, in an effort to improve reliability. However, his ideas were put to the wayside as traditional turbo technology was seen as a safer venture, as well as a more relevant option for use in future Ferrari road cars.

Aside from the reliability issues, the Comprex suffered from two main drawbacks compared to the turbo unit. As the exhaust gases effectively shared a space with the intake air inside the cell rotor, even for a brief moment, some of it was inevitably mixed in, causing excessive exhaust gas recirculation, sullying the air/fuel mixture and diminishing performance.

Additionally, the hot exhaust mingling with the cooler intake air combined with the resulting compression significantly raised the temperature of the intake air. The raised temperatures caused the system to yield less power than the twin turbo approach.

The only fix would be to incorporate a large intercooler. But since packaging was an issue, and the same technology could be applied to the turbo car for even more power, this was a lost cause. Lastly, the Comprex setup was far bulkier than the turbo, requiring an extended high cowling which disturbed airflow to the rear wing. In any case, the innovative 126CX failed to match its brutish brother on virtually all points.

With just one outing in practice, the 126CX became both the first and the last Comprex-powered racing car, as the turbo finally got a vice-like grip on the sport in the years to come. The technology wasn't lost entirely though, as it found a home in the diesel industry, where the increased intake temperatures were actually helpful to their compression-ignition operation.

Finnish tractor company Valmet introduced the Comprex-driven 411CX engine as early as 1980, and Japanese car maker Mazda finally brought the technology to the passenger car market with the advent of the 2.0L four cylinder RFT diesel engine fitted to the Mazda 626/Capella in 1987.