Both forms of forced induction that we know of, superchargers and turbochargers, are naturally flawed in some respects. A supercharger is great for producing immediate power and torque in lower operating ranges by deriving its energy directly off of the belt, commonly being done in a positive-displacement system by utilizing a belt that the crankshaft drives in order for the screws in the compressor to spin and compress the air to increase the pressure and/or density of the air entering the engine, but it generally means that fuel economy won’t be as great as the engine’s efficiency could be (if it were naturally aspirated) and that at higher operating ranges, the supercharger begins to draw more power from the engine to produce more power, with the compressor leeching off of the potential power supply in order to function.
If this isn’t a suitable option, a turbocharger’s promises of much more power and torque, higher efficiency and fuel economy due to running off of the exhaust gases, having less reciprocating and rotational mass (in smaller engines), and greater quantities of power being produced regardless of engine size also seem attractive. The exhaust gases from its respective manifold propel the turbine’s blades (which are connected to a turbine that drives the compressor that pressurizes the air in the air filter and manifold with a shaft that shoves more air into the system) increase the fuel-air ratio, but they need to accumulate in order for the compressor to spin, with this process waiting being labelled “turbo lag.” On larger turbochargers, this boost can come on suddenly and powerfully, and it occurs when the boost threshold is reached, with this form of forced induction creating power higher in the operating range due to relying on exhaust gases.
For performance applications, there’s one solution to both systems’ shortcomings. By using both forms of forced induction in one engine, the supercharger is able to make its power in the lower operating range as the turbocharger spools up, and when the turbocharger comes on boost and creates its power, it takes over for the supercharger as it begins to leech off of the power supply. Along with this, compounding allows for the air compression to be much greater than just adding the amount of boost that the supercharger and turbocharger individually produce, with large amounts of boost possibly being created by (relatively) low-cost components.
The twincharger exists in two forms: series and parallel. The former, the most common arrangement, is where one compressor’s output feeds another’s inlet, which can occur in either the turbocharger or the supercharger. The former is of medium or large size, and the supercharger is sequentially-organized, which provides manifold pressure for boost almost instantaneously as the larger turbocharger begins to spool up. As the turbocharger reaches its operating speed and creates its pressure, the supercharger can continue to compound the pressurized air to the turbocharger’s inlet to create higher intake pressures or be bypassed and/or mechanically decoupled from the drivetrain through the use of an electromagnetic clutch and a bypass valve, which would be a move that’s in favor of the induction system’s fuel efficiency.
Without this bypass system, both compressors can operate at the same time, with compounded boost, where air that was compressed previously in the first stage with the supercharger is compressed again in the second stage when the turbocharger activates, resulting from this system. The amount of compounded boost that’s created from this kind of series system is the product that occurs from multiplying the pressure ratios, explaining the larger amount of power that can be created from these systems when the compressors run in synchronicity. By using this system without a bypass, one can obtain boost pressures that wouldn’t be possible with other kinds of arrangements with the compressor and would, as a result, operate inefficiently. The issue with this system, however, is that the thermal efficiency in both compressors are multiplied together, with the supercharger’s inefficiency skewing the better efficiency granted by the turbocharger. Unless large amounts of cooling are provided by the intercooler, the manifold can reach high temperatures and suffer a decrease in reliability. Along with this , the supercharger also needs a larger amount of energy to power it than the turbocharger, and if the former is bypassed, there’ll only be slight parasitic losses from spinning its working components due to removing the load of performing compression, with the slight losses being removed completely by intervening electrically with the aforementioned clutch disconnect.
The latter arrangement, that of the parallel kind (also know as an inline arrangement), usually uses a bypass or diverter valve in order to allow one or both of the compressors to create boost within the manifold. Without the bypass, if both compressors were routed directly to the intake manifold, the supercharger would blow backwards into the turbocharger’s compressor instead of into the intake because of the former having the path of least resistance, which warrants the need for the diverter valve in order for the turbocharger’s air to be vented until it reaches the necessary pressure in the intake manifold, with this method needing complex and/or expensive electronic devices to ensure that the power delivery throughout the operating range is smooth. When the turbocharger successfully spools up, the supercharger stops operating once the electronic relay or diverter halts it, with this method being the one that the Volkswagen Auto Group used in the 1.4 TSI.
Such complex and expensive electronic components are the downfall of the twincharger as a whole. In order to have a responsive, smooth delivery ow power and large gain of power, many of these components are needed to control the pressure that’s created, and in a spark-ignition engine (usually gasoline-powered engines), a low compression ratio is a must in the case that the supercharger creates large quantities of boost, which would bring a low-displacement engine’s efficiency into conflict with the increase in performance. Along with this is the inherent gain in weight by using the two differing compressors, which brings a (slight) decrease in performance and efficiency due to the extra weight being pulled about by the vehicle.
Due to such complexity and operating costs, many manufacturers decide against using this form of aspiration, but there is an increase in interest for this form of aspiration, with aftermarket twincharger conversion kits being available from different companies for such cars as the Toyota MR2, the Ford Mustang, and the Subaru Impreza. There were, however, a few manufacturers that decided to experiment with the two differing compressors, with their attempts being documented in the creation of the following cars, which range from normal commuters to obstreperous, race-ready machines.
Lancia Delta S4
Resplendent in its Martini livery, the Delta S4 was a widowmaker in a hot hatch’s clothing, a car that found flinging itself around and off of a course (and off of a hill) an enjoyable activity that it usually frequented in the hands of Henri Toivonen. Placing the engine, an inline-four with dual overhead cams that, in total, used sixteen valves, behind the driver’s head in a move similar to Peugeot with their rampant, dominant 205 T16, it put out a conservatively-rated 480 HP, with some reports claiming that the evolved engine from the 037 had a power figure looked to be closer to 560 HP. By keeping the displacement at 1,759 cc, Lancia’s engineers were able to sneak into the under 2,500 cc class by multiplying the four-pot’s capacity by 1.4, which allowed the car to weigh a lithe 890 kilograms (1,962 pounds).
Appearing at first in 1985, the car was called a Delta only for marketing purposes; they didn’t even share door handles due to the lack of them on the car, with the doors being opened by a small loop. Beneath its driver was an all-wheel drive mechanism developed with Hewland that had a center differential that allowed 60-75% of the torque to be sent to the rear wheels. Such torque, being developed on the lower end of the operating range, would be produced by only the turbocharger at higher engine speeds due to a bypass valve disabling the supercharger at these higher velocities. Surrounding the driver was a tubular space frame chassis, which was connected to four long-travel double wishbones, and bodywork molded into fully-removable front and rear sections by carbon-fiber composites.
Such was its formation that an opening in the hood behind the front-mounted water radiator with a Gurney flap, a front spiltter and its associated winglets, a flexible front skirt, and a rear deck wing that consisted of a full aerofoil wind section and a deflection spoiler were all molded and incorporated into the body’s design to ensure that the car would reach third and second in the 1985 and 1986 championships respectively.
Such an application of this aspiration in rally inspired two designers in 2009 from Denmark, the same country that creates Legos and emissions-free electricity, to create the Zenvo ST1, an 1,104 HP answer to (relatively) new companies like Koenigsegg and Pagani. Everything involving this car was hand-crafted, save for a high-performance, five-axis CNC router, and in the middle of this car sat a 6.8 liter V8 that had the supercharger and turbocharger bolted onto it. This allows the car to produce this four-digit output at 6,900 RPM, with 1,050 lb-ft of torque preceding it at 4,500 RPM, allowing the car to spring from a standstill to sixty-two in about three seconds, charge on to 124 MPH after 8.9 seconds, and fly on the ground at speeds of 233 MPH. The body, forged from carbon fiber, comes from Germany, and different components on it, including the gauges, gas tank, ABS system, traction control, and airbags, originate from German and/or American cars.
While such parts were borrowed from different manufacturers, Zenvo states that the basis for its design, for all 3,721 pounds of its features, body, and massive heart, was a result of Danish design, which is a form of functionalistic design that evolved from the school of Bauhaus, and as Danish designers utilized new technologies, they would mesh them together with simple ideas that were focused more on an object’s purpose.
The body’s designed for what it’s supposed to do: to offer respite to the sweltering power plant and channel the air in such a way that it’s able to avoid taking off. It was available not only with a seven-speed dual-clutch sequential gearbox by Xtrac, but also a robust six-speed stick shift by Ricardo, which can be especially helpful in roasting the 345-section rear tires.
The steel backbone connects to the wheels through double-wishbone setups with Öhlins adjustable dampers being what control spring oscillation in the springs. Three settings limit the amount of power on hand, with normal freeing 650 HP, sport sporting 850 HP, and race unleashing the maximum amount of power, and concerning traction control, while it’s fully operational in normal mode, it has limited availability in sport and is completely absent in race mode, with this making such a vehicle rather dangerous even in its lowest power setting.
Nissan March (or Micra) Super Turbo
This, however, is a car that can be utilized daily while sporting a twincharged engine; it only makes 110 horsepower from its twincharged 930cc engine. On one side of the block, there’s a turbocharger, and on the other, there’s a supercharger, and the latter is able to produce 10 psi of boost until approximately 4,000 RPM, where the former boosts the amount of pressure to 14 psi to the 6,500 RPM redline. To determine whether it’s best to utilize the compressor, a magnetic clutch activates it, doing so under hard throttle to bypass turbo lag and disengaging when it spools up and takes over. Considering this, the passenger hops between these ranges in the operating range through the use of a five-speed manual shifter. Known as the PLASMA MA09ERT, the “PLASMA” was an acronym for “Powerful and economic, Light, Accurate, Silent, Mighty, Advanced,” which is an acrostic that perfectly fits the puny pugilist.
Where the previous two examples of twincharging were extreme, high-performance applications that pushed the boundaries of what internal combustion was capable of, the Super Turbo was the first car of its kind that one could buy at a reasonable price and enjoy, with there being a reasonable quantity of these cars for the public to purchase and utilize. This homologated version weighed 1,697.56 pounds, with this weight increase being due to the addition of several features that were necessary for daily driving. There was also another version of this, the 1988 March R, that used the same engine as the Super Turbo, but the former was sold with four-point harnesses for the seats, a wheel designed for racing, a taller gear shifter, and a lack of a rear spoiler, which was featured on the Super Turbo.
Where the R is a race car for the people, the Super Turbo is the homologation special for the people, with this being done to allow the car to race in the 1988 All-Japan Rally Championship alongside the Bluebird SSS-R. It was the fastest Micra in Nissan’s history, reaching 62 MPH in 7.7 seconds and powering on to 112 MPH, and considering this, it gave people an inkling of what the two compressors held in potential.
Any Car from the Volkswagen Auto Group that Uses the 1.4 TSI Engine
Continuing to impress people, the dynamic duo appeared again with the arrival of the 1.4 TSI, a 1,390cc engine that found widespread usage in the Volkswagen Auto Group due to its versatility in fuel economy and performance. Eight power ratings were available, ranging from 138 HP and 162 lb-ft of torque in the Volkswagen Golf (generation five), the Volkswagen Jetta (generation five), and the Volkswagen Touran to 182 HP and 184 lb-ft of torque in the Audi A1. In a Golf with either 120 or 158 HP, the car was rated at six liters per 100 kilometers (on the Euro-cycle), and its cousin, the 177 HP Polo GTI, was rated at 5.9 liters per 100 kilometers. For being such a versatile power plant that could be adjusted for numerous applications, major promise could be seen in the four-cylinder, being able to provide the torque of a corresponding 2.3 liter engine, but with 20% less fuel consumption.
To craft such an engine, Volkswagen chose a direct-injected FSI system from its EA111 engine series, which is commonly seen in the Golf. After this, they needed to create a bulletproof cast-iron cylinder crankcase to withstand the higher pressures brought by twincharging (for example, the 1.4 TSI is able to produce 36.26 psi of boost in a Golf GT 1.4 TSI), and a coolant pump with an integrated magnetic clutch and a supercharger were installed shortly after. The injection system was then modified to include the first multiple-hole, high-pressure injection valve with six fuel outlet elements, and the injector was arranged on the intake side between the intake port and the cylinder head seal level, like that in a naturally-aspirated FSI engine. The maximum injection pressure was increased to 150 bar (2,175.57 psi) in order for the engine to support the differing amounts in the quantity of fuel needed throughout the operating range, and a Roots-type supercharger was selected for a compressor.
Due to the two counter-rotating screws, the air is moved as a fixed volume of air per rotation, with this occurring in the intake manifold, and this is connected with the turbocharger in a series where a control valve makes certain that the fresh air needed for a certain state can enter either the exhaust turbocharger or the compressor. Despite the resulting praise and accolades, Volkswagen decided that it would be best to terminate the project after its healthy run, citing complexity and costs as a major issue and their belief that more advanced technologies that were applied to turbochargers can achieve similar results to the twincharger at a greatly reduced cost.
Any Volvo that Uses the Volvo Engine Petrol Four in the T6/T8
Still finding promise and interest in the method, Volvo decided to apply it to their newest engines, those used for the T6 and T8 models in their lineup. Over the lower-spec T5 engine, the supercharger allows the T6 engine to produce approximately 140 lb-ft more torque when it’s just off of its idle. Interestingly, the turbocharger in Volvo’s twincharged engine activates earlier than others, doing so around 1,500-1,600 RPM, and it allows the T6 to maintain its peak torque past 4,500 RPM. When this torque begins to wane, it does so in a manner that turbocharger-only engines can’t, in that it decreases more gradually. Idle air first flows into the supercharger, then into the turbocharger, and finally into the engine, with this being done in order to benefit the car’s low-end responses to the accelerator being depressed, but also to assist with spinning the turbine more quickly.
At a predetermined point in the code of a car’s computer, approximately 3,500 RPM, a butterfly valve opens to bypass the supercharger and de-clutch it in order to prevent its inherent loss of power, with the results of a low-end supercharger and a high-end turbocharger creating horsepower and torque curves that can rival those of three-liter twin-scroll turbocharged inline-sixes, including that of its idle, length of the torque’s metaphorical plateau, and higher operating ranges. Along with this, Volvo innovated further with the engine, including a variable speed electric water pump that cools the engine, direct injection to increase the efficiency of an explosion within a cylinder, and low friction bearings and rings to make the components operate more fluidly.
Due to such innovations, an XC60 with this engine in the 304-horsepower T6 trim can earn 29 MPG, which is a 50% increase over the fuel economy of a V8-powered XC90 in 2009, and it has more torque being produced at a lower operating range than that of any other two-liter four-cylinder engine in the United States.
However, others pine for the losses of the same company’s six-cylinder and eight-cylinder engines, meaning that Volvo may need to ignore some people as the issue of emissions slowly, but surely, strangles all cars.
What, then, is the future of the twincharger? Will companies continue to utilize an ingenious device like this or leave it to find a home with another? The aftermarket continues to hold a strong following for twincharged vehicles, but the government is eventually going to find a way to phase out certain technologies. The twincharger is a fun alternative to the harsh reality of emissions and fuel economy regulations, one that promises that us petrolheads and politicians can eat cake together and get along, where one gets performance and the other gets better results from the pipe and the pump. Manufacturers, automobile or aftermarket, can try everything in their power to make certain that the twincharger survives due to its potential, but in the end, laws, not wills, usually dictate what occurs.