Secondary air injection on gasoline engines

The secondary air injection system of gasoline engines ensures a reduced emission of pollutants in the warm-up phase when starting the engine. During this time, the engine requires a mixture with fuel surplus until reaching the operating temperature, with the result that some of the fuel leaves the combustion chamber unburned. Since the lambda control and the catalytic converter don’t have the time to warm up during the cold start phase, the harmful hydrocarbons and carbon monoxides can be released into the environment without aftertreatment. For this purpose, the secondary air system is installed behind the outlet valves.

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Power loss of internal combustion engines – Problems & How to Repair

Over time, internal combustion engines may lose their performance due to a variety of reasons. Mainly because of the aging of the engine, the burning process no longer runs too frictionless and ‘smoothly’ as at the beginning. For this purpose, the air and fuel supply, as well as the compression and ignition play an important role. Continue reading “Power loss of internal combustion engines – Problems & How to Repair”

Mercedes-Benz 300 SL: The legendary “Gullwing” of the 1950s

Mercedes 300 SL

The Mercedes-Benz 300 SL (W 198) was presented together with the smaller 190 SL in February 1954 at the International Motor Sports Show in New York. It was offered in the years 1954 to 1957 as a coupe with gullwing doors and in the years 1957 to 1963 as a roadster. The 300 stands for the engine capacity measured in cubic centimeters, the additional designation SL is the short form for “super-leicht” (german: super-light). Alternatively, it is claimed that the letters were derived from “sport-leicht”.

Mercedes-Benz 300 SL (W 198)

The original 300 SL, the Mercedes-Benz W 194 racing car, achieved unexpected success in 1952. The even faster road version (W 198) was with a top speed of 230 km/h the fastest sports car of its time.

The Gullwing

The body of the 300 SL was shaped as streamlined as possible. In order to keep the frontal area small, the bodywork was slightly retracted from the window line. Only after the construction of the frame, which went far to the top, it was noticeable that conventional doors could not be used because of the frame construction on the vehicle flanks. Despite the misconception that the doors are mere stylistic affectations, the eye-catching “gullwings” were necessary because of the vehicle design. A total of 1400 gullwing cars were built,  while most of them were exported to the United States.

The body of the 300 SL consisted largely of sheet steel. The hood, the trunk lid, the sill and the doors, however, were made of aluminum. On request and for a relatively small extra charge, the entire body was made of light metal, which made the vehicle 80 kilograms lighter. But only very few customers chose that option, making those versions very rare and sought after today.

Mercedes-Benz 300 SL Gullwing

The little brother: Mercedes-Benz 190 SL

Next to the Mercedes 300 SL, Daimler-Benz introduced the Mercedes 190 SL (W 121) in February 1954 at the International Motor Sports Show in New York. By 1963, a total of 25,881 units of the “Tourensportwagen” (engl.: “touring sports car”) had been built, of which almost half were exported to the United States. Many stylistic elements such as front mask, bumpers and headlights have been adopted from the 300 SL. The 190 SL was available either as a convertible or as a coupe with removable roof. Today one would probably call it a convertible with hardtop.

The concept of the open two-seater 190 SL with an easy-to-use weatherproof soft top was so successful that in the following, the 300 SL was modified accordingly. The legendary gullwing was replaced in the spring of 1957 by a roadster variant (W 198 II).

The convertible top of the 300 SL could be stored under a separate flap behind the seats and was easy to operate. The grid frame of the roadster variant needed to be changed in the area of the doors and the rear. Thus, normal fortified doors with much more comfortable entry were able to be installed.

Mercedes-Benz 300 SL (W 198)

The new technology: direct fuel injection

The first automotive direct injection system was produced by Bosch and was developed by Goliath and Gutbrod in 1952. The Mercedes-Benz 300 SL became in 1955 the first production sports car with four-stroke engine to be equipped with a direct fuel injection system. The Bosch fuel injectors were placed into the bores on the cylinder wall,  and the spark plugs were relocated to the cylinder head. The result was a boost in engine output and efficiency and would remain a signature feature of the 300 SL “Gullwing” for a long time.

Mercedes-Benz 300 SL


The Mercedes-Benz 300 SL was also very popular among replica manufacturers. Therefore, Mercedes-Benz had the design of the vehicle protected and banned the reproduction of the 300 SL in court. Previously, there were replicas from Germany and Switzerland, which were offered under the name Gullwing and Gullwing Roadster.

Turbo-compound engine: The “cooler” turbocharger

A turbo-compound engine uses the exhaust gases through a downstream turbine. This can be installed in addition to a turbocharger.

While the first exhaust gas turbocharger provides more boost pressure in the combustion chamber due to the exhaust gas energy and thus higher engine power, the second turbocharger converts the remaining energy into movement power. The generated energy is passed on to the crankshaft via a mechanical or hydraulic transmission.

Porsche 919 Hybrid Motor Turbo Compound Technik
In the 2.0L V4 engine of the Porsche 919 Hybrid, a system with the hot exhaust gas flow drives a generator with the turbo-compound technology, which in turn generates additional electrical energy. (Picture: manufacturer)

The overall complexity of a turbo-compound system and especially for road vehicles quite low saving effect has prevented widespread introduction of the turbo-compound engine.

Mercedes CLS Coupe 218: The luxury Benz with retro flair

Introduced in January 2011, the Mercedes CLS (218) is the second generation of the CLS series. Based on the platform of the E-Class, it is available as a four-door coupé or as a Shooting Brake.

The predecessor

The first generation of the Mercedes CLS (W219) was launched in 2004 and had its run until 2011. By that time it was unclear weather the market would receive a four-door coupe with no technical advantages to the other models in the Mercedes-Benz lineup. Neither did the CLS offer more performance than the E-class it was based on, nor did it come with a bigger interior. It even offered less headroom and poorer visibility than the conventional Mercedes sedans. What distinguished the CLS, however, was the exterior design, designed in 2001 by Michael Fink. The elegantly curved body impressed the customers, and by 2010 more than 170,000 vehicles were sold. The brave step of Mercedes paid off, and the CLS established itself successfully as the first four-door coupe on the market. The success of the Mercedes CLS also inspired other manufacturers such as VW, BMW or Aston Martin, who followed up with similar concepts.


The CLS of the 218 series was initially available in 2011 with V6 petrol and diesel engines. Later followed by a 4-cylinder diesel, as well as two V8 gasoline engines. The most powerful engine on the market is the CLS 63 AMG with a 5.5-liter V8 with direct injection and twin turbocharging. The resulting power is 535 hp (386 kW), which can be increased to 557 hp (409 kW) with the optional AMG performance package.

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Mercedes SLK R172 – The transition to the SLC

The Mercedes SLK R172 is the third generation of the 1996 introduced SLK series. It was built from 2011 to 2016, after which it has been named Mercedes SLC since the facelift. The long bonnet and the far rear passenger compartment are typical for Mercedes sports cars. The expressive styling is reflected in the front with the diamond grill. In the silhouette, the sporty styling continues in details such as air intakes with fins in silver chrome.

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The Steering: From the steering wheel to the steering axle

The steering is generally a part of the chassis, and responsible for the directional control of the vehicle. It allows the driver to influence the direction of travel by turning the wheels of the front steering axle in the desired direction.


In the basic principle, the movement of the steering wheel is transmitted via the steering column to the steering gear, which transmits the movement in direct or indirect form to the tie rods.

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The Exhaust System

The exhaust system receives the exhaust gases escaping from the exhaust valves of the cylinders through the exhaust manifold. These are attenuated in their noise generation after they have been cleaned in the catalyst, and discharged into the environment at a suitable part of the vehicle. The entire system is connected to the underside of the vehicle with the vehicle floor.

Direct Fuel Injection

In a diesel or gasoline engine with direct fuel injection, the fuel is injected through a nozzle with up to 200 bar directly into the combustion chamber. This mixes with the air that was introduced through the inlet valve. In gasoline engines with direct injection gasoline is supplied mainly in the compression stroke. In diesel engines, however, this happens at the beginning of the power stroke.

BMW High Precision Injection (Source: Manufacturer)

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Turbocharger: How Exhaust Gases Increase Engine Power

A turbocharger (also exhaust gas turbocharger) uses the energy that is lost by the exhaust gas of a reciprocating engine, profitable for driving the cylinder. It compresses the combustion air supplied to the engine, providing more torque and an increase in engine power.

In a normal reciprocating engine, the amount of air needed for combustion in the intake stroke is drawn by the piston into the cylinder. This type of engines are therefore also called ‘naturally aspirated’. For high performance engines, the movement of the piston alone is not enough to get enough air into the cylinder. Therefore turbochargers are used, which provide for a higher oxygen content in the combustion chamber of the engine.


In essence, a turbocharger consists of a centripetal turbine connected by a fixed shaft to a centrifugal compressor. The exhaust gas stream sets the turbine wheel in rotation. Its torque and speed is transmitted via the common shaft to the compressor wheel in the intake system.


How a Turbocharger works

When using a turbocharger, the thermal energy of the exhaust gases is converted into kinetic energy. The exhaust gases drive the turbine, which in turn chases fresh air through the compressor. The compressor compresses the fresh air, which is then passed through the intercooler back into the cylinder. This results in a better filling of the cylinder compared to pure naturally aspirated engines. The result is higher engine performance with lower fuel consumption and better emissions.

As long as enough exhaust gas flows, the speed is sufficient to generate an overpressure on the intake side. But this condition is reached only at higher gas flow rates from engine speeds of about 1500 to 2000 rpm, so that turbo engines operate in the lower speed range as naturally aspirated and delayed response to sudden acceleration.


The Intercooler

The intercooler is installed between the turbocharger and the intake valve. It cools the air heated by the charge. Since cold air takes up less space, more oxygen fits into the combustion chamber. Cooling also thermally relieves components of the engine (cylinders, valves, pistons, spark plugs, etc.). Intercoolers themselves are either air or water cooled.

AMG 5.5-liter V8 engine: twin turbocharger with intercooler (Source: Manufacturer)

The Turbo Lag

In older turbochargers, a certain speed was required for the charge. In the low speed range, the amount of exhaust gas is insufficient to produce the required boost pressure for the turbocharger. Even with more modern engines, the onset of the turbocharger requires some time in stationary accelerations, since the turbine must first be sufficiently accelerated by the exhaust gas flow. As the size of the turbocharger increases, it takes longer for the compression to take place. This delay until the action of the turbocharger is called turbo lag.

Mercedes AMG GT Biturbo turbochargers
Mercedes AMG GT with biturbo-marking in the side gills.


Bi-turbochargers (also: twin-turbo) are two parallel turbochargers. They are powered by two cylinders of the engine, which allows them to work more efficiently.

Sequential bi-turbochargers do not charge both chargers continuously. As soon as higher engine power is demanded, the second turbocharger is activated. Typically, bi-turbochargers are installed in larger engines, where manufacturers want to keep fuel consumption low.

Turbo-Compound Engine

In addition to a regular turbocharger, the exhaust gas energy can also be utilized by the turbo-compound technology. For this purpose, an additional turbine is switched, whereby the remaining energy is transmitted in the form of kinetic energy to the crankshaft.

VTG Superchargers

Turbochargers with variable turbine geometry (also VTG superchargers) have adjustable vanes on the input side of conventional turbochargers. These become steeper with increasing exhaust gas quantity, which increases the cross section.

With a VTG charger, the turbo lag can be reduced or even avoided. A large engine torque is possible in the lower and upper speed range. However, if the engine is adjusted incorrectly or the car used for sort distances only, the VTG-adjustment can be contaminated by exhaust gas residues.

Turbocharger Porsche Turbo

VTG Turbocharger of the Porsche 911 Turbo (997). With the variable turbine geometry, the cross sections of the optimum load size are simulated by vanes that are located in the exhaust gas flow. 


In addition to cars with petrol or diesel engines, turbochargers are also used in aircraft and ships. In planes, where the power of the engine decreases with increasing altitude, it can be counteracted with a turbocharger. In addition, turbochargers allow for downsizing in engine size, which saves additional weight through a smaller unit.

While in the early days the increase in performance was predominantly the reason for the engine’s charging, nowadays the main focus is on reducing emissions. For this purpose, more and more car manufacturers rely on smaller engine sizes with correspondingly optimized turbocharging.

Turbocharger: Pros / Cons

A turbocharger allows a higher maximum mean pressure and thus an increase in torque and maximum power at a given displacement. This increase either results in a more powerful engine of approximately the same size and weight as the original, uncharged engine, or allows the same power to be obtained from a smaller unit.

In addition to the many advantages, turbochargers also bring some disadvantages. The use of a turbocharger leads to higher mechanical and thermal loads as well as higher mean pressures. Therefore, many components in the engine such as e.g. Engine block and cylinder are designed to be more resistant. These measures generally increase vehicle weight.