In 1977, the FIA allowed turbocharged 1.5-liter engines into Formula 1 to compete against the existing 3-liter normally aspirated units. Two years later, when Renault recorded its first win with the turbocharged RS 10, Ferrari knew the technology held great promise for the future.
“We clearly understood that was the right road to follow,” said Ferrari’s chief of race-car engineering Mauro Forghieri, who had held the post since 1962. “We couldn’t obtain more than 515 bhp from a 3-liter normally aspirated unit—with a rev limiter, due to the ignition distributors of the period—but with the turbocharged 1,500-cc engine we aimed at a starting point of 550 bhp.”
With its comprehensive in-house manufacturing facilities, recent history of high-performance engineering, and close links with qualified suppliers, Ferrari was well-prepared to jump aboard the turbocharged bandwagon. To exploit boosting’s potential, Ferrari produced a new car, the 126 C, which was first shown to the press in June 1980 and demonstrated to the public in practice for Monza that September.
“I was probably one of the few who had some notion of it all,” said Forghieri about forced induction, “due to my passion for aeronautical piston and turbine engines. Rocchi and Salvarani were not far from retirement, but in the meantime engineers Luciano Caruso and Nicola Materazzi had arrived, so we designed a V6 engine with 120-degree cylinder banks. This was a layout of proven success that had won the World Championships for Phil Hill and Ferrari in 1961. It was a highly advanced unit into which we poured everything we had learned with the flat-12, including short exhausts at the center to avoid high-temperature problems under the monocoque.”
Claude Seippel’s 1940 patent of the Comprex principle.
By this, the engineer meant that the usual arrangement of ports was reversed, with the exhausts in the center of the vee and the inlets on the outside. Also unusual was that, in addition to developing a traditional turbocharger setup, Ferrari used the innovative Comprex pressure-wave supercharger, conceived by Swiss company Brown Boveri (also known as BBC).
“It was based on a rotor powered by an engine-driven belt,” explained Forghieri. “Exhaust gas passed into the end of the rotor and initiated a resonance in many small rotating channels, or cells, that compressed the air delivery that then flowed into the engine. With the Comprex, the engine ran like a normally aspirated unit with almost all the advantages of the turbocharger.”
In 1940, Switzerland’s Claude Seippel, working with BBC, patented a rotating drum with longitudinal passages at its periphery as a “pressure exchanger.” It wasn’t until after World War II that such a radical idea could be realized industrially, and by the late 1970s BBC was progressing with its introduction of the Comprex to the larger motor industry. Its aim was to make practical a concept that was by no means new but still promising enough to create “another turbocharger business,” as a BBC executive said when expressing his company’s hopes for its success.
“The Comprex obviously is not a turbocharger,” explained engineer Charles Amann, “but it performs the same function—using the energy in the exhaust gas to increase the density of the air entering the engine. The Comprex incorporates a cylindrical rotor containing a series of longitudinal annular cells. The revolving rotor is typically belt-driven. On the inlet end of the rotor, atmospheric air is ducted into part of the annulus and compressed air leaves over the rest. On the opposite end of the rotor, cylinder-exhaust gas is ducted into part of the annulus and the exhaust gas leaves at essentially atmospheric pressure over the rest. Within the rotor passages, the exhaust pressure waves compress the fresh-air charge.
Schematic shows how rotating drum uses exhaust gases to create boost.
“Compared to the turbocharger,” Amann continued, “the Comprex enjoys a much lower rotational speed. Because the cell walls are exposed alternately to both exhaust gas and fresh air, they run at a lower temperature than turbine blades. That eases the materials problem. The overall efficiency of the Comprex is in the same ballpark as that of a turbocharger. Being run from the engine, the Comprex escapes the acceleration-lag problem that haunts the turbocharger in road vehicles.”
Compared to the turbocharger, which was disadvantaged in racing applications by its delayed throttle response, or lag, the Comprex delivered boost pressure that rose much more consistently and steadily with engine speed. This promised to be more effective on Formula 1’s road circuits.
“Enzo ordered me to take on the new technology,” said Forghieri. “I didn’t have the slightest doubt of the correctness of his decision. The engine continued to be at the epicenter of a car project to the Commendatore, but it was significant that a man of over 80 years had decided to disrupt the technical objectives of his company with a choice which, at the time, was by no means commonplace.”
FROM 1979, FERRARI AND BROWN BOVERI agreed to work jointly and exclusively to exploit this new and attractive concept for motor racing. By that time, under the direction of BBC’s Andreas Mayer, the Comprex program had led to 70 inventions and nine patents concerning the device’s construction, adaptation to engines, and emissions issues. BBC was also evaluating its installation in road cars, producing several in substantial volumes. Now, with the Comprex effort led by Ernst Jenny, BBC welcomed the cooperation with Ferrari, which had the potential to make motor-racing history.
Cross section of Comprex’s internals.
“We tested the Comprex for a long time,” said Forghieri, “and negotiated an interesting exclusive agreement with the Swiss company. Among the Comprex’s good qualities was the absence of the turbo’s high delivery temperature, to the extent that we could use a simple air-to-air intercooler. But it was also heavy and raised the car’s center of gravity.”
Enzo Ferrari himself reportedly devised a way to use the impulse patterns of the Comprex to create an intercooling effect. After extensive dynamometer testing, the CX 160 Comprex, 6.3 inches in diameter, first enhanced the power of a Ferrari Grand Prix car in December 1980. Tested just before Christmas at the Fiorano track, the 126 CX gave far better throttle response than twin turbos and good mid-range power. However, the Comprex engine could not challenge the turbocharged V6’s peak output, and the car weighed 44 pounds more.
“Three weeks later,” said Belgian reporter Paul Frère, “both the Comprex car and a turbocharged car were taken for several days’ testing on the Paul Ricard circuit in the South of France. To everyone’s surprise, the Comprex car lapped faster than the turbocharged version. True, the times were not quite up to those of the Renault and Alfa—fastest at that time—but the object of the tests was to develop the engines, so practically no work had been done either on the running gear or on aerodynamics.”
In the Ferrari, the Comprex’s rotating drum was powered at up to 30,000 rpm by a toothed belt driven by an exposed jackshaft that ran along the top of the V6 from the camshaft gear train at the rear (clutch end) of the engine. Pressurized air from the charger went forward to the intercooler, from which it was split to smaller coolers at the sides of the body in advance of the inlet manifolds.
Mechanical layout of basic Comprex system.
“The spent exhaust gases exit by way of a large megaphone with an internal baffle,” Britain’s Denis Jenkinson reported. “The noise emitted is a very satisfyingly ‘different’ sound, very shrill and very ‘tight,’ unlike the ‘knackered Formula Ford’ sound of a turbocharged layout.”
“The Comprex has a rather flat boost curve,” Frère wrote in Motor after discussions with BBC engineer G. M. Schruf, “so the boost pressure remains roughly constant over a fairly wide range of operation. To some extent the peak of the curve can be moved up or down the engine revolution range by altering the drum speed relative to engine speed. In the case of the Ferrari, the ratio is approximately 1.2:1.
“The boost curve obtained is rather similar to that given by a positive-displacement supercharger,” Frère had learned, “rising, as clearance leaks decrease, until a certain critical engine speed is reached. Peak power is given where optimum resonance is obtained in the Comprex. Output starts to decrease when the optimum resonance speed is exceeded and the rotor’s various pipes suffer increased pressure drops. The shape of the curve and the maximum boost pressure obtainable are obviously also dependent on the Comprex’s size.
“In the Ferrari installation,” continued Frère, “in order to flatten the curve further and to feed the engine at the highest pressure at which it will operate reliably on commercial fuel over the widest possible operating range—from about 6,000 to some 11,000 rpm—a waste gate is used to cut off the highest part of the curve. This pressure-limiting valve can be small compared with that required by a turbocharger because it has to handle only about one-fifth of the volume of gases.”
Mauro Forghieri, chief of race-car engineering, oversaw the Scuderia’s Comprex efforts.
Concluded Frère, “Of course, the major feature of the Comprex is that the response to opening the throttle is virtually as immediate as in a normally aspirated engine. As soon as exhaust gases are produced, boost pressure builds up to its maximum. In its present stage of development, the Comprex-supercharged engine apparently develops slightly less power than its turbocharged counterpart, fed at the same boost pressure. This may be caused by a slightly higher exhaust back pressure. According to Ing. Schruf, it is about 20-percent higher than the boost pressure, whereas, to my knowledge, the exhaust back pressure caused by a turbocharger blowing at that sort of pressure is about equal to the boost pressure, or slightly less.”
GILLES VILLENEUVE AND DIDIER PIRONI tested both the Comprex (126 CX) and turbocharged (126 CK) versions of the new Ferrari extensively over the winter of 1980-81. With its better throttle response, the Comprex-equipped car was seen as potentially superior for the race on the streets of Long Beach, California on March 15—an event that officially opened the 1981 season after the South African Grand Prix was excluded from the World Championship. Two of the three Ferraris prepared for the Long Beach race were shipped to California with Comprex-compressed engines.
BBC project manager Tony Köllbrunner was happy with this choice. His reasoning was that because Long Beach was a multi-cornered street circuit, the Comprex’s better low-speed responsiveness would prevail. In pre-race practice, wrote Denis Jenkinson, “it was pretty obvious which system Ferrari was concentrating on, with Brown Boveri engineers in attendance, Brown Boveri advertising on the side of the car, and, apparently, an exclusive contract with the Swiss firm for this season, much to the chagrin of Renault.
“The Scuderia Ferrari started off with all their efforts centered on the Brown Boveri Comprex supercharging system,” added Jenkinson, “both drivers using this layout. But Gilles Villeneuve had the drive belt to the supercharger break. While he was out in the T-car, fitted with twin KKK turbochargers, he not only went a lot faster but also was faster than Didier Pironi with the other Comprex.”
Comprex supercharger fitted to 126 CX.
Both drivers then switched to the turbocharged 126 CK, qualifying fifth and 11th, although both would retire with engine-related problems. Since this was the first race entry for a completely new car as well as a new engine system, it was to be expected that the Ferraris were not at the front in either qualifying or the race. But the Scuderia’s practice experience showed that the Comprex-blown engines had limitations which hadn’t been revealed by tests on the dynamometer or at Fiorano.
“While practicing for the United States Grand Prix West at Long Beach, it became clear that a system was necessary to keep the Comprex drive belt from breaking,” recalls Forghieri. “That happened because of the speed variation between one gear change and another and the subsequent inertia. We didn’t come across that problem at Fiorano, a circuit that didn’t impose great differences of that kind.”
Long Beach, with its harsh acceleration demands and bumpy surface, revealed the weakness. The rotor’s inertia loadings were too high to permit the belt to survive.
BBC’s Köllbrunner had misjudged the nature of Formula 1 racing. The benefits of his Comprex could have been demonstrated at Long Beach, to be sure, but its faults were fatally manifested there, as well. Ferrari asked BBC to develop a smaller rotor that would have less inertia, but this was not made available. Later in 1981, a Comprex-equipped engine was taken to South America for the Grands Prix in Argentina and Brazil, but it was not used in a race. This was in fact the ultimate fate of the Comprex, which never saw a starting flag.
“I suggested the development of a system with a hydraulic coupling,” said Forghieri, “and spoke to the Brown Boveri technicians about it. They agreed, but the BBC directors requested a contribution of about a billion lire towards the work.”
That would have amounted to more than one million dollars. Unfortunately, neither side could afford the experiment, and so the Comprex exited the world of motorsport. The innovative compressor did achieve production status in diesel-powered passenger cars, but in racing the power potential and reliability of turbochargers won the day.
