Turbolader technology

A patent in the German Reich was filed for the turbocharger by its inventor Alfred Büchi in 1905. The turbocharger boosts the degree of efficiency of combustion engines. Büchi’s invention was constantly further developed and optimized. Today, the turbocharger achieves amazing results.

How is a turbocharger built?

The turbocharger consists of

  • an exhaust turbine that is driven by the exhaust gases of the engine,
  • a shaft, which in turn is driven by the exhaust turbine and
  • a fresh gas turbine on the other side of the shaft that, through the shaft’s mechanical energy fed to it, takes in the air and feeds it to the engine.

State-of-the-art turbochargers achieve shaft speeds of over 200,000 rpm; in addition, a turbocharger is exposed to exhaust gas temperatures of over 1,000°C (1,832 °F). This leads to high material stresses that can reach the endurance limit.

Why you should never accelerate the rotating parts of a turbocharger with compressed air

If the turbocharger exceeds its burst speed, the centrifugal force on the turbine wheels is so great that either the exhaust gas turbine or the fresh gas turbine break. When this occurs, it’s like an explosion; in particularly severe cases, they might even break through the housing.

Why should a turbo engine be warmed up slowly?

In principle, every engine you want to possess for a longer period of time ought to be warmed up slowly. This way, the piston and other components can reach their operating temperature slowly and hence the right expansion in relation to their opposite component. Moreover, there is no excessive wear.

Things are similar for the turbocharger. If you warm it up very quickly by demanding a great deal of load from a cold engine, high exhaust gas temperatures evolve and the heat will not be distributed evenly in the charger. This can lead to material deformation, cracks and increased bearing load. In addition, the turbocharger is lubricated by engine oil. If the oil has not yet reached its operating temperature, its lubrication properties are also sub-optimal.

So if you like your turbocharger and engine, you should keep an eye on the oil temperature gauge and only load the engine fully once 80°C (176 °F) has been reached.

Why should turbo engines be started up cold and be left running idly awhile after shutting them off?

The lower the temperature and the speed of the turbine wheels in the turbocharger are prior to shutting off the engine, the better it is for the charger. While the engine is still running, the turbocharger is still supplied with fresh lubricant from the engine’s oil pump, so heat can be dissipated. In addition, depending on the load, a certain air flow is drawn through the fresh gas turbine, which also has a cooling effect. Most chargers also have an inlet and outlet for the water coolant, which are supplied by the water coolant pump of the engine.

When you now shut off the engine and the cooling with oil, fresh air and coolant stops, heat accumulates in the turbocharger: The temperature moves from the exhaust housing into the basic unit with the bearings up to the fresh gas side, since these components are no longer cooled. If this occurs too quickly, it can lead to material deformation and heat cracks. The gaskets and bearings also have a high thermal load in this case. The oil in the bearings can overheat and leave carbonization. Moreover, the water coolant in the housing channels of the charger can boil and, owing to the formation of vapor bubbles, lead to uncooled hot spots.

“I can’t help thinking of the poor turbocharger in my neighbor’s Golf TDI every time the car is tortured up the driveway still in second gear almost at full throttle, and then the engine is shut off immediately. The engine control still tries to get as much as possible boost because a lot of torque is used. The charger is accelerated to the maximum as good as it can be done at low engine speeds, and when it has reached about 10,000 rpm, lubrication and cooling are simply snatched away from it. Not good at all!” –Bartek

If you are simply a driver and don’t tinker on your vehicle or don’t do it too much, you only have to pay heed to careful warming up and cooling down at this point and can continue to look around in the shop. If you want to know more technically, you definitely should read on.

My turbocharger is defective. Can I repair it myself?

If the damage is on the housing halves or to an internal wastegate, the housing halves can be replaced; this also applies to parts of the wastegate and the actuator. Often, tuning parts are available for this, for instance turbine housing from TiAL for Garrett turbochargers or the actuators by Forge. But if it’s the turbines that are damaged (e.g. bearing damage), only a turbo repairer can help. Because as soon as you loosen the nut, the part is no longer balanced. Since it can be re-balanced only on special balancing benches for turbochargers, you ought to keep your hands away from it in your own workshop.

What must be considered when there is any damage to the turbocharger?

First of all, the reason for the damage must be carefully analyzed and remedied before the installation of a new turbocharger. It is also vital to ensure that all intake passages and charge air passages are carefully cleaned. The exhaust manifold must also be cleaned to prevent shavings or broken parts from flying into the new, rotating turbocharger or the engine.

What must be considered when installing a turbocharger?

  • The oil feed lines and oil drainage lines should always be replaced, since they might be clogged.
  • It is also recommended to install a new air filter, so the new turbo can breathe freely and its performance won’t be limited.
  • All gaskets associated with the turbocharger should be replaced. If, for instance, a manifold gasket on a cylinder is leaking, the turbocharger won’t get the full exhaust gas quantity, similar to the case of a slightly open wastegate. Then the whole boost controller cannot work properly, and a small defect has a severe impact.

I would like to install a larger turbocharger to increase performance. What do I have to be aware of?

First of all, you should consider how much performance you want. It’s silly to install a larger charger if you only have a vague idea. You should fall back on known turbo kits for which empirical values exist with respect to the performance that can be achieved with them. If you want to investigate the matter further and you trust yourself with putting together the turbo kit on your own, you ought to get acquainted with the interpretation of the compressor map and turbine map of turbochargers. Unfortunately, you’ll need a little math for that.

How can I interpret the compressor map?

Air quantity/air mass (x-axis):

For the performance, decisive is how much air quantity or air mass the turbocharger can provide. Unfortunately, the specifications of the manufacturers differ quite a bit. Garrett specifies the air mass in lb/min., for instance. 10 lb/min. are good for an engine output of about 100 hp. A turbocharger creating 50 lb/min. at a 2 bar boost therefore creates 500 hp at a 2 bar boost, provided of course that the engine is able to process this air mass at a 2 bar boost.

For those who want to convert the information to the metric specifications of other manufacturers: 10 lb/min. is about 4.538 kg/min. If you want to convert it to air volume, the air pressure and the temperature must be taken into account. 1013.25 hPa air pressure and 15°C (59 °F) temperature equals an air density of 1.225 kg/m³. This means that 10 lb/min. -> 4.538 kg/min. x 1.225 kg/m³ = ~5.56 m³/min., or ~5560 l/min. go through an engine, with 100 hp power output.

Boost/compression rate (y-axis):

Anybody dealing with turbochargers should know the boost. The boost is built up when more air volume or air mass is provided to the engine than the engine would be able to process without charging as a naturally aspirated engine.

So if the throughput of the engine is increased, e.g. by camshafts with longer control times, the boost falls with the same flow of the compressor. The processed air mass increases, however, so the performance is increased despite the diminished boost.

The boost is not directly shown in the compressor map but as compression rate before the compressor to compression rate after the compressor. Given a compression rate of 2.5, the boost is about 1.5 bar (simply compression rate minus 1).

What constitutes a good turbo exhaust manifold?

A differentiation must be made between constant-pressure turbocharger manifolds and pulse turbocharger manifolds.

Constant-pressure turbocharger manifolds are mostly used on standard engines but are also available for tuning. They are suitable for narrow spaces. With a constant-pressure turbocharger manifold, the channels of the individual cylinders are brought together by the shortest route in front of the turbocharger. An exhaust accumulation forms in front of the turbocharger, by which the exhaust turbine is driven. Constant-pressure turbocharger manifolds are usually cast parts, sometimes welded designs. If you want to achieve a slight increase of the performance output, a constant-pressure turbocharger manifold is the right thing; or you can simply use a turbocharger that fits your standard manifold.



If you want to make use of all their advantages, pulse turbocharger manifolds are the ne plus ultra in turbo engine design. They usually consist of very twisted, welded pipe designs with the same pipe length as far as possible from the individual cylinders to the turbocharger. A pulse turbocharger manifold should not only drive the turbine by the exhaust accumulation but also by the pulse energy of the exhaust gases coming out of the outlet valve. Therefore these manifolds must be as flow-enhancing as possible and must be designed taking account of the firing order.

Example: With a 4-cylinder engine, the firing order is 1-3-4-2. When all the pipes come together in front of the turbocharger in a 4-in-1 plenum, the pipes ought to arrive at the plenum in such a way that there is a swirl in the exhaust gas flow. Cylinder 1 next to 3, 4 next to 3 and 2 next to 4. This way, the pressure impulses of the cylinders go round in a circle and create a swirl. In addition, the pressure waves can impact the exhaust turbine in an even sequence.

To stay with our example: If you have a turbocharger with a twin-scroll exhaust gas housing, the cylinders with the greatest firing distance should always be combined, i.e. 1 with 4 and 3 with 2, or, in a 6-cylinder engine with the firing order of 1-5-3-6-2-4 and a twin-scroll housing, cylinders 1-2-3 and 5-6-4.

You should always take great care and check that a turbocharger is made of heat-resistant and scaling-resistant material as far as possible. They are very hard to find, but the absolutely optimal turbo exhaust manifolds are those with plugged-in or removable plenums, since the plug connection prevents heat deformations. The manifolds can thus be made of thin-walled pipes without them tearing. In the case of manifolds with plugged-in plenums, the design and choice of material are more important than the material thickness with respect to the question of whether cracks will occur in the course of time.

Make your own turbo manifold – with flanges from BAR-TEK®

Anybody who wants to build his own manifold can get the right flanges at our shop. They are made of heat-resistant stainless steel. Even if you just want to identify a flange on a part, these drawings are helpful. Here is a summary of the most common flanges; special flanges are available on request.







T4 Devided




Twin scroll/single scroll: Single-scroll or twin-scroll exhaust side – what is the difference?

As of a certain charger size, single-scroll or twin-scroll turbine housings are available. A twin-scroll turbine housing improves the response of the charger only if you build a matching pulse turbocharger manifold for it. Given a 4-cylinder engine with the firing order of 1-3-4-2, for example, the two cylinders with the greatest firing interval must go to one channel in the turbine housing. This means: cylinders 1+4 and cylinders 2+3 must go together. This results in a torque-oriented manifold guide for the engine as in a 4-in-2-in-1 manifold.

You should avoid installing a divided turbine housing with a manifold that first brings together all 4 cylinders and then divides the exhaust flow again. This is not what turbochargers are for, and the response at lower engine speeds will be not good. In such cases, a single-scroll turbine housing is preferable.

If you want to have a good response and not too high exhaust back pressure despite a large turbocharger and are able to build a matching exhaust manifold, to boot, you should not hesitate to use a twin-scroll housing. For constant-pressure charging and smaller chargers, it is not worth the effort, though. Both versions certainly have their justification.

What do I have to consider in terms of air intake?

The most important aspect is that the turbocharger takes in as much air as possible, which is as cool as possible and as dry as possible, with a flow resistance that is as low as possible. This one sentence actually says it all – to implement it might be a bit more difficult.

First, you should ensure that the filter area of the air filter element is not too small, since otherwise the flow resistance is too high.

Example: The air filter of a Porsche GT3 with 435 hp has the dimensions: 178 mm x 522 mm. So without taking account of the folded air filter element, the area is 92916 mm². This corresponds to 92916 mm²/435 hp = 213.6 mm²/hp. As a car manufacturer, Porsche most certainly is not keen on throttling back the performance of its engines on account of the air filter throughput, so this value is useful to calculate the size of the filter area you need for your turbo project.

Unfortunately, you often see large filters in conversions but they often sit in the engine compartment unprotected. They draw too much warm air, and performance is wasted. But if you study the three basics thoroughly, you can find a good solution for every conversion.

How do I recognize a good performance intercooler?

The intercooler should have as low a resistance as possible to the charge air flow and cool the air down as far as possible. For this, the side boxes must have a flow-friendly shape, and the cooler must have a large surface. With the large surface, the number of channels in the cooler increases and thus the cross section through which the charge air can flow. You also ought to make sure – especially if the water cooler is located behind the intercooler – that the radiator block is not too thick. Although the cross section for the charge air is reduced again with a thin radiator block, the air stream can flow better through the cooler. If the charge air encounters little resistance but is not sufficiently cooled down due to poor air stream flow, you’re back to square one. So you fare best in finding a large-surface cooler with a thin radiator block and flow-friendly side boxes that, ideally, can be installed in the vehicle with little effort.



What is a wastegate?

The wastegate is a bypass of the exhaust gas turbine, guiding the exhaust gas past the turbine. When the wastegate is open, the turbine is no longer driven by the exhaust gas. Then the speed of the turbocharger decreases. Depending on how wide the wastegate is opened, the boost is reduced or even completely dissipated. The wastegate is usually controlled with a linkage and an actuator. In order to control the actuator, a clock valve is usually put in upstream.



Is it better to use an external or an internal wastegate?

In most cases, smaller chargers are equipped with internal wastegates; larger turbochargers often require an additional, external wastegate. Usually, internal wastegates are well adapted to the charger already at the factory. You will likely have to experiment somewhat with an external wastegate, but it might well achieve better results than an internal one.

In order to find the right solution for one’s own conversion, you first must check how much space there is in the engine compartment and which charger size you actually want to use. You should know how much boost you want for what displacement and approximately which performance you want to hit. Then you should consider how the available space should be used and how all components can be installed in a flow-friendly way without creating thermal problems. So your creativity is in demand!

How does the boost controller work?

When the wastegate opens, a part of the exhaust gas can flow past the turbine of the turbocharger. This causes the turbocharger to be less strongly driven, and the boost is reduced. The valve or flap of the wastegate is controlled by a diaphragm capsule. The boost affects one side of the diaphragm, the force of a spring works on the other side. When the boost exceeds the force of the spring, the wastegate opens. So in order to set the boost at which the wastegate opens, you can increase or reduce the spring pre-load or install a harder or softer spring. If the wastegate is used without control, only a fixed maximum boost can be set.

If you want to set the maximum boost during driving, a boost controller must be installed in the boost line to the wastegate. It is vital in this context that the spring and spring pre-load in the wastegate are always designed for the lowest maximum boost you want to drive. The boost controller works like an adjustable leakage. The more you open the boost controller, the more boost is released and the less boost arrives at the diaphragm capsule.

Example: The wastegate would open at 0.6 bar when the boost controller is closed. If the boost controller is opened to the extent that, given a 1.0 bar boost, only 0.5 bar arrive at the diaphragm capsule, the wastegate opens only at 1.1 bar or 1.2 bar.

An electronic boost controller works similarly. Instead of working mechanically, an electronic boost controller has an electromagnetic valve (called a N75-valve at VAG, for instance), which is triggered at a specific frequency. If it is triggered with a frequency of 50 Hz, it can be triggered 50 times per second, i.e. every 20 msec (milliseconds). So if it is triggered 50 times per second with 10 msec, i.e. with 50% of the signal length, it opens approximately halfway. 5 msec trigger time would open the valve 25%, etc.

The electronics of the engine control device or electronic boost controller can thus control the switch-on time and determine how much boost is passed to the diaphragm capsule. An electronic boost controller has the advantage that you can set a different boost according to engine temperature, engine speed or other parameters. This means it is considerably more flexible but also technically far more complex.

A good example of electronic boost control is the over-boost function. Some vehicles have it ex factory. Among others, the old Audi 5-cylinder turbo engine allows, at full acceleration, a 0.2 bar higher boost for a time of about 30 seconds. How long and whether the over-boost function is used at all is described in the program of the boost controller and can be changed only by chip tuning, for instance.



What does the A/R ratio express?

A/R stands for “radius over area” on the turbocharger housing; or put simply: It expresses how strongly the flow cross section in the turbocharger housing has changed beyond its radius or has not.

For example, compare two housings of an exhaust gas turbine: The one has an A/R of 0.82, the other an A/R of 1.01. So both have the same inlet cross section on the manifold flange, given the same flange form (e.g. T4 flange). In the housing with an A/R of 0.82, though, the cross section decreases significantly faster than in the housing with an A/R of 1.01. In most cases, you can infer it from the external dimensions of the exhaust housings. The same applies to compressor housings. The flow goes through them the other way around, however, so the cross section increases in the course of the flow instead of decreasing. Normally, the manufacturers of the compressor housings always have a fixed A/R and offer different housings with different A/Rs and/or flange shapes for the exhaust side. The turbine maps are therefore furnished with different characteristics for the different A/Rs. Basically, one can say: the smaller the A/R, the quicker the charger responds but also the more exhaust gas accumulation it causes at higher speeds. With a large A/R, it is the other way around.

How can I interpret the exhaust gas turbine map?

The map shows what performance the turbocharger generates at what speed. The map of the exhaust gas turbine has the compression rate marked on the x-axis. This does not indicate the intake air to compressed air but the exhaust gas pressure before the turbine to the exhaust gas pressure after the turbine. The mass flow for the exhaust gases can be read on the y-axis.

What are the differences of turbochargers made by KKK, Garret, Borg Warner and Turbonetics

KKK chargers

KKK chargers are often installed in series-production vehicles. In the area of tuning, chargers of larger engines are often installed on smaller engines. The most common charger series by KKK have slide bearings. The upgrade chargers are a combination of the original exhaust turbine, partially with a different A/R on the housing, and a larger compressor from a charger for larger engines. KKK provides virtually all parts for their turbochargers. This way, turbocharger repairmen can combine parts of different chargers without any problem. Unfortunately, KKK supplies little information, so maps of compressors or turbines are hard to find; and, when you use chargers, parts of which had been combined from two or more turbochargers, even this information would be of no use. With KKK chargers, you should collect information in advance from people who have already used something similar beforehand and how it went.

Garrett chargers

With Garrett chargers, the information situation is much better. Maps of compressors and turbines are available for every charger from the normal range. All Garrett chargers with an “R” added to their names are equipped with ball bearings on the main shaft. The ball bearings allow for faster revving up of the rotating equipment. By revving up the rotating equipment faster, the response will be quicker – given an even charger geometry – compared to slide bearings, and the boost is built up more quickly as well.

Garrett turbochargers with ball bearings should always be driven with an oil restrictor, because the bearings and gaskets are designed for a high oil pressure. You should always order the oil restrictor together with the charger.

The Garrett GTX turbochargers have the same design as the GT chargers of the same name. Only the compressor wheel is different. The GTX compressor wheels are made from a forged blank instead of a cast blank; they are brought into a flow-optimized shape with a CNC mill. With this, the GTX charger range manages more air mass and higher boosts.

EFR chargers

The EFR charger range by Borg Warner presents the technological state of the art at present. All EFR chargers have dual ceramic ball bearings and an oil restrictor that is integrated in the housing. The forged compressor wheels have been finished so finely with the CNC mill that they look almost polished. The compressor housings have been optimized to the flow on the intake side and on the pressure side. Even a blow-off valve has been integrated in a flow-enhancing way. The compressor side has a solenoid valve for the triggering of the wastegate in chargers with internal wastegate. The compressor housing also has a semi-finished drill hole with an M6 internal thread. When you remove the compressor housing and complete the drilling, a speed sensor can be inserted there. Although Borg Warner does not offer any evaluation electronics for this, you can monitor the charger speed during test bench runs and thus – together with the boost – define exactly at which point in its maps the charger currently stands.

If you look at the exhaust side of the EFR chargers, you can see that Borg Warner offers the smaller chargers of the range complete with T25 flanges and only one A/R for the exhaust housing. The larger chargers are offered with three different A/Rs; the housing with the smallest A/R always has a T25 flange and an internal wastegate. The medium-sized housing has a two-part T4 flange and also an internal wastegate; the large housings are also equipped with a divided T4 flange; they have no internal wastegate, however, and must be driven with an external wastegate. All EFR chargers have a built-in turbine made of lightweight and high temperature-resistant gamma titanium. This material cannot be clearly classified as ceramics or metal. The reduced masses in connection with the ball bearings make for a very fast response and a high speed stability of the rotating equipment. With the material used, exhaust gas temperatures of up to 1050 degrees Celsius (1922 °F) can be driven. With chargers of other manufacturers, this can be done only for a very short time. With other chargers, you had better be careful with temperatures from 900-950 degrees (1652 - 1742 °F).

The Borg Warner EFR range is to be recommended from A to Z. It is a pity, though, that most of the larger chargers are not available yet from Borg Warner.


Turbonetics has a very wide range of turbochargers for the tuning range. Compressor and turbine maps are not available for all chargers, though. But Turbonetics has an application list that offers good orientation.

Once you know what performance you want to achieve with what displacement, you get right to the charger you need. Depending on the charger series, Turbonetics offers various compressor sides with “anti-surge” drill holes or “high-flow” geometry. The drill holes for anti-surge go from the intake flange straight up to the turbine. This allows some air to flow past the turbine at low speeds if the compressor does not provide enough air. The compressor map becomes wider and with it the usable speed range of the engine. The boost is reduced more quickly. These compressor sides allow for a somewhat lower boost, though. The high-flow compressor sides work at lower speeds like a compressor side with a normal geometry. But since they have a larger intake cross section and quarter-circles are machined around the compressor inlet, more air from the side can flow to the intake head. On account of this improved flow, these compressor housings have a slightly higher flow volume and a slightly higher boost at high speeds. With some charger ranges, Turbonetics, like Garrett, offers chargers with ceramic ball bearings that show a significantly better response than the usual slide bearings.

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