Knowledge engine tuning
Worth knowing about the engine tuning and turbo conversions
We do not just want to sell you something, we also want to advise you correctly. In the text below, we have compiled the most important technical background information on the topic of engines and turbos, to give you a basic knowledge. With that facts we aware you of a bad buy and you will get the best out for your project. If you still have questions, you can reach our technical hotline at +49 (0) 30/991 94 99 95.
You should have the largest possible pipe diameter, mufflers without large constrictions and only a few but generous elbows, because the turbine lives from the temperature gradient, which of course is higher with less exhaust back pressure. In exhaust noise behavior, the turbo engine is quieter compared to a naturally aspirated engine because the turbine absorbs some of the noises and acts like a silencer.
He is thermally loaded higher in the turbo engine as the naturally aspirated engine. On the one hand due to the higher back pressure up to the turbinr housing and on the other hand, it still has to absorb the weight of the turbo and wastegate. As a result, the exhaust manifold works more and needs high-quality materials (also for seals, screws, nuts). There are 2 ways to use the exhaust energy: pulse turbocharging and congestion charging (more on that below).
This is at a turbo gasoline engine at 850 ° C to about 950 ° C. Under full load, may be slightly higher (depending on the engine software programming), but should remain below 1050 ° C, otherwise there is a high probability of a too lean mixture. For turbo engines, the temperature should be measured in or near the turbo (if possible always before).
The shortest possible intercooler pipes with a few but generous bends and thus a small intake pipe volume ensure a fast response with the lowest possible pressure and throttling losses.
The turbine size of the turbocharger largely influences the volume flow rate. The A / R ratio is a method of fine tuning. The A describes the turbine inlet cross section and the speed with which the gases hit the Turbine Wheel. A smaller cross-section thus causes higher gas velocities. The R describes the entry angle of the gases on the Turbine Wheel. If it is small, higher turbine speed occurs. A small A / R ratio stands for faster response, a bigger A / R for more power and less back pressure at high rpm.
Electronical / Mechanical Boost Control Valve
Electronic / mechanical boost controllers offer the possibility of adjusting the boost pressure without having to change anything in the basic setting of the wastegate. The pressure line to the wastegate is narrowed / manipulated so that the wastegate (valve / flap) remains closed up to the desired or set boost pressure. So the wastegate "thinks", the boost set value is not yet reached.
The turbocharger has an efficiency of about 75%, which is higher, the less a heating effect of the boosted air takes place. That means, the higher the efficiency, the lower the temperature that the turbo delivers (on the compressor side) and the less backpressure (heat) on the exhaust side. This back pressure causes high temperatures between turbine and combustion chamber, which may need to be counteracted (sodium-cooled valves, larger exhaust system, oil and water cooler).
In the interest of a high performance engine, a metal catalyst should be always used in a boosted engine since it has larger cross-sections in the honeycomb structure than ceramic cat's. It thus contributes to reducing the back pressure in the exhaust system.
Compressor & Turbine Maps
The maps of the compressor and the turbine are their performance diagrams, which allow conclusions about their efficiency and behavior. The compressor map compares the pressure ratio with the volume flow (speed / throughput). The left-side of the efficiency lines represents the surge limit. Here no throughput takes place, since the air flow breaks off at the compressor blades. This happens, for example, when the throttle valve is closed, when a high pressure builds up, but the volume flow is small. Backward curved blade ends, as well as a recirculation valve can prevent backflow of the gases and thus shift the limit positively. On the right side, the efficiency clams reach the choke line. Here the throughput is limited at high volume flows. At this limit, the compressor is at the limit of its capacity, which happens when the speed of sound is reached at the compressor wheel. By returning each second compressor wheel blade, manufacturers achieve a delay in the choke line. The turbine map compares the turbine pressure ratio to the flow rate. The behavior of the turbine is determined by the temperature and pressure gradient before and after the impeller.
In addition to the increase in density (boost pressure build-up), the turbocharger also causes an undesirable increase in the temperature of the charge air, which represents a higher engine stress (knock limit, combustion chamber temperature, pressure,…). Furthermore, the hotter the air, the less the density, so less oxygen and less engine power. The goal is to cool the air, which the IC does. Its advantages are: more power, torque, compression, stability, pre-ignition and less boost pressure with the same power, consumption and octane requirement. The size of the ICdepends on the amount of air to be passed through and the charge air temperature. See air / air IC and water / air IC.
He is the most common type of intercooler. This is cooled by the air flowing through the ambient air (wind). When placing it is advantageous if the radiator is placed neither in front of another radiator or behind, to be able to flow as freely as possible from the wind. If this is not possible due to the structural conditions (intercooler size, no space in the front of the vehicle ...), it should at least be the first radiator in the airstream. An improvement in efficiency can also achieve cooling air ducts. From the construction method, a large area, low cooling network depth (air flow through intercooler is better) and a high back pressure of the airstream are the best (with excessive turbulence, however, blocking flows occur). Here is the conflict between low pressure loss of the charge air (high cooling network depth) and high cooling efficiency (sufficient turbulence). An efficiency advantage can be achieved by spraying water against the radiator (especially on hot summer days).
He is a bit more complicated than an air-to-air intercooler. Because here are actually two coolers available. One that cools the boosted air while it is surrounded by water, and a corresponding separate water cooler installed in the front of the vehicle (normally less than air-to-air intercooler). The circulation of the water is created by an electric pump. For full-load trips (1/4 mile), there are also similar dry ice intercooler, which have an extremely high efficiency during racing and also contribute to a very short charge air line (fast response), just like the air-to-water intercoolers.
To make it resistant to the increased temperatures and pressures, there are the following options: high-quality bearings for connecting rods and crankshafts, forged connecting rods, forged pistons, stronger valve springs, bolts / screws for connecting rods, optimized cylinder heads, a nitrided crankshaft, and a stable cylinder head gasket. Occasionally, even diesel blocks / crankshafts (1.8l Petrol / 1.9l Diesel ...) are used, since they are designed for higher combustion pressures. The elevated temperatures are affected by additional oil cooler, additional water cooler, oil splash cooling of the piston crowns, sodium-cooled outlet valves, increased speed and earlier switch-on point of the fans.
Sodium Cooled Exhaust Valves
They are a way to account for the increased temperatures of a turbo engine and are available on almost all standard supercharged engines. While the intake valves (300°C up to 500°C) are cooled relatively well by the incoming gases, the outlet valves (up to more than 700°C) are heated much more strongly by the exhaust gases. The sodium filling can reduce the temperatures by up to 100°C.
Extremely high duration cam shafts with long opening times and large valve lifts are not required for a turbo engine as opposed to the naturally aspirated engines to achieve high performance. Due to the high pressure in the manifold, they can cause a large part of the exhaust gases to get back into the combustion chamber.
You should not have any chambers and constrictions, especially at high boost pressures, as this will increase the back pressure, which negatively affects the performance ability of the turbocharger. The exhaust system should be as large as possible during turbo operation, in the interest of high horsepower and be equipped with generous radiuses.
Pulse Charging Principle
It uses the heat energy of the exhaust gases, which is created by the pressure and temperature gradient before and after the turbine. Here, the exhaust gases are led in front of the turbine in a common collector, the pressure conditions remain almost constant.
Back Pressure Charging
This utilizes the energy of the exhaust gas velocity of the individual engine cylinders, which are led up to the turbine separately (exhaust manifolds). If a separation is no longer possible, only the lines of the cylinder with the largest firing intervals should be merged. The back-pressure charging creates fluctuating pressure conditions in front of the turbine wheel, which results in advantages in terms of efficiency and response.
It describes the dimension between housing and turbine / compressor wheel. Part of the air escapes through this column, which of course is bad for the efficiency. The S. should be as small as possible, but large enough to ensure a sufficient clearance in the radial and axial direction of the wheel. These tolerances the wheel needs to compensate for the leverage and bending vibrations.
Blow Off Valve / Pop Off Valve
They are integrated into the charge air line in front of the throttle valve. It has the effect of changing gears and releasing sudden gas, ie jerky / fast closing of the throttle valve, preventing backflow of the already conveyed charge air to the compressor wheel. If such high-pressure oscillations occur, this may even damage the compressor wheel. The recirculation valve thus "detects" when the pressure rises sharply and returns the excess charge air back into the intake area in front of the compressor side, with even the compressor wheel remaining at high speed for a longer time. The blow-off valve works just as well, up to that it simply releases the excess air into the environment (engine compartment).
It consists essentially of the constant bearing housing and at the ends of a turbine and compressor housing, in each of which a paddle wheel is located, which are rigidly connected to a shaft (in bearing housing). The turbine housing is mounted directly on the exhaust manifold. The turbine wheel is driven by the exhaust gases of the engine. Since both wheels are rigidly connected, now turns the compressor wheel with and sucks in turn fresh air. At high enough engine speeds, pressure builds up, allowing the engine to deliver much more oxygen than it would be able to suck in, resulting in a higher engine performance (assuming enough fuel). The bearing housing should be water cooled as this drastically reduces the risk of coking the oil.
The task of the turbine side is to supply the Compressor Wheel with energy so that it delivers the required air flow and pressure fast enough. At the same exhaust gas ratios, a small turbine responds faster than a large one, but provides a higher exhaust back pressure at high engine speeds, which presents the difficulty in selecting turbine size.
Describes the relationship between the inlet and outlet diameters on the compressor and turbine side. The wheel geometry is particularly important because even the smallest differences cause large differences in the diameters. On the turbine side, a large trim causes less backpressure after the turbine (high efficiency), on the compressor side there is a large trim for higher throughput even at low pressure.
The wastegate control via wastegate / wastegate actuator is the most common and best type. Here, a part of the exhaust gases is routed around the turbine wheel as soon as the desired boost pressure is reached. The control thereby WG is the best possible, yet it wastes valuable exhaust energy. The valve / flap opens even before the turbo reaches the desired pressure in order to redirect enough exhaust gases at maximum pressure. This energy could thus be used to accelerate the turbine wheel before it has reached the target speed. The internal WG / wastegate actuator is installed in / on the turbo itself. A disadvantage of this system is that the diverted exhaust flows directly behind the turbine wheel before the exhaust pipe (downpipe) again with the exhaust gas, which drove the turbine, comes together, causing high turbulence there. In the case of the external WG these two exhaust gas streams are / should be merged much later at a freely selectable location (minimum distance from the turbine outlet should be about 50 cm), where e.g. also a cross-sectional enlargement can take place. This external WG in turn has the disadvantage that it can form vortex already in front of the turbine in a non-optimal arrangement, which disturb the main mass flow. The WG outlet in the exhaust manifold should optimally be in the flow of all cylinders, outgoing at a shallow angle from the main mass flow (no right angle) and symmetrically flowed with the turbine housing.
The water injection or water-ethanol injection is an optimization option for turbo engines. This sounds strange at first, but you can install a W. behind the intercooler. This water is now supplied to the engine in small quantities and it evaporates on its way into the combustion chamber due to the relatively high temperatures. Here it achieves the positive effect of lowering the temperature of the charge air (lower temp. = More Oxygen = more Performance ....).
A good efficiency of the compressor side is determined by the pressure ratio and the volume flow. At the optimum size, the efficiency optimum (about 75%) must be positioned in an often used speed range. The lower the efficiency, the higher the temperatures, i. The efficiency should be kept as high as possible over the entire rev range.
The compression ratio determines the economic efficiency, performance at certain boost pressure, the turbo lag, the required octane number of the fuel and intercooler efficiency. However, it must be reduced in the turbo engine due to the higher temperatures and pressures compared to a naturally aspirated engine. Usually about 7 up to 8,5:1.
Compression Reduction Plate
Compaction reduction by means of an intermediate plate is the simplest method of lowering the compression ratio to a turbo-standard level, whereby the other engine components are usually retained. For the VR6, for example, a spacer sleeve must be used for the chain tensioner. As a result, the tax times are shifted in the direction of early. The performance of turbocharged engines is inherently low in compression, with a further reduction due to thicker cylinder head gaskets.
Cylinder Head Machining
It should not be too strong. If so, then in the outlet channels as possible only a smoothing or very small channel extension should be made. The combustion chambers and intake channels can be a generous treatment "treat". However, due to the higher temperatures and pressures during turbo operation, a little less work should also be done here. Great attention should be paid to the transitions of the intake manifold to cylinder head, cylinder head outlet to exhaust manifold and exhaust manifold to turbocharger inlet. In a professional processing also seat rings for valves and their shank are enlarged. Other valves required.
Many thanks for the support to Stefan Pieper (VW-Heideseen).