Engine Tuning - Basic knowledge explained by TurboZentrum
It is important for us not just to sell something, we want to consult and be your project partner. So that our customers can understand what they are buying and get the best out of their project, we also teach knowledge. What can I optimize on the engine and what do I also have to pay attention to? When it comes to engine tuning and its definition, most people get into trouble. The costs and complexity of engine tuning is dependent on how much more power is needed. Often it is not enough just to switch certain parts for better ones, because they must work together and have to be tuned on each other. On the other side you can, specially with turbo engines, get a significant increase of power with a few simple steps. We have collected the most important technical basics about engine and turbo tuning and explain their function to bring more light into the darkness. If you are planning a modification and have further questions, please contact us.
Turbocharger, Wastegate, Blow Off and Co.
It essentially consists of the central bearing housing and, at the ends, a turbine and compressor housing in each of both of which there is a paddle wheel fixed rigidly to a shaft (in the bearing housing). The turbine housing is mounted directly on the exhaust manifold. And the turbine wheel is driven by the exhaust gases of the engine. Since both wheels are rigidly connected, the compressor wheel rotates with them and intakes fresh air. At high enough engine speeds, a pressure build-up occurs, whereby the engine can be supplied with considerably more air than it could suck in itself, which in turn, assuming enough fuel, results in a higher engine power. The bearing housing should be water-cooled, as this drastically reduces the risk of coking of 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. With the same exhaust gas ratios, a small turbine responds faster than a large one, but offers a higher exhaust back pressure at high speeds, which is the difficulty in selecting the turbine size.
A good efficiency of the compressor side is determined by the pressure ratio and the volume flow. At the optimum size, the optimum efficiency (about 75%) must be positioned in a speed range that is often used. The lower the efficiency, the higher the temperatures, i.e. the efficiency should be kept as high as possible over the entire speed range.
The performance maps of the compressor and the turbine are their performance diagrams. Which allow conclusions to be drawn about their efficiency and behaviour. The compressor performance map compares the pressure ratio with the volume flow (speed/throughput). The left-sided limitation of the efficiency mussels represents the pumping limit, here no more throughput takes place, since the air flow breaks off at the compressor blades. This happens, for example, when the throttle damper is closed, when a high pressure builds up but the volume flow is low. Backward curved blade ends and a circulating air valve can prevent backflow of the gases and thus positively shift the limit. On the right side the efficiency mussels reach the stuffing limit, here the flow rate is limited at high volume flows. At this limit, the compressor is at the limit of its flow rate, which happens when sound velocity is reached at the compressor wheel. By displacing every second impeller blade back, manufacturers achieve a delay in the stuffing limit. The turbine map compares the turbine pressure ratio with the turbine throughput. The behaviour of the turbine is determined by the temperature and pressure gradient before and after the blade wheel.
The charge pressure control by means of wastegate / pressure can is the most common and best way. A part of the exhaust gases is led around the turbine wheel as soon as the desired boost pressure is reached. The control by means of WG is the best possible, yet it wastes valuable exhaust gas energy. This is because the valve / flap opens even before the turbo reaches the desired pressure so that sufficient exhaust gas can be diverted at maximum pressure, so this energy could still be used to accelerate the turbine wheel before it has reached the target speed. The internal WG / pressuredose is installed in / at the turbo itself. A disadvantage of this system is that the diverted exhaust gas is usually directly behind the turbine wheel, in front of the exhaust pipe (Y-pipe) again with the exhaust gas which drives the turbine wheel comes together, resulting in high turbulence there. With the external WG, these two exhaust gas streams are / should be brought together much later to a freely selectable location (minimum distance from the turbine outlet should be approx. 50 cm), where e.g. a cross-sectional expansion can also take place. This external WG in turn has the disadvantage that, if not optimally arranged, it can form vortices in front of the turbine which disturb the main mass flow. The WG-exhaust in the exhaust manifold should ideally be located in the volume flow of all cylinders, at a flat angle from the main mass flow (no right angle) and symmetrically flowed to the turbine housing.
Steam wheels offer the possibility to adjust the boost pressure without having to change the basic setting of the wastegate/pressure can. Here the pressure line to the wastegate is narrowed/manipulated so that the wastegate valve/flap remains closed up to the desired or set pressure. So the Wastegate "thinks" the fixed value is not yet reached.
They are integrated into the charge air line upstream of the throttle valve. It causes the throttle valve to close abruptly when gear changes and sudden throttling occur, i.e. no backflow of the charge air already conveyed hits the compressor wheel. If such high pressure oscillations occur, this can even damage the compressor wheel. The recirculation valve "detects" when the pressure rises abruptly and releases the excess charge air back into the intake area before the compressor side, so that even the compressor wheel remains at high speed for longer. The blow-off valve works the same way, except that it simply releases the excess air into the environment (engine compartment).
The shortest possible charge air lines with few but generous bends and thus low suction pipe volume result in a fast response with the lowest possible pressure and throttle losses.
In addition to the increase in density (boost pressure build-up), there is also an undesirable increase in the temperature of the charge air in the turbocharger, which represents a higher engine load (knock limit, combustion chamber temperature, pressure, etc.). Furthermore, the warmer the air, the less density it has, i.e. less oxygen and less engine power. So the goal is to cool the air, which the Intercooler does. Its advantages are: more power, torque, compression, stability, pre-ignition, as well as less boost pressure at the same power, consumption and octane rating. The size of the Intercooler depends on the amount of air to be forced through and the charge air temperature. See Air-Air Intercooler and Air-Water Intercooler.
Air-Air Intercooler - It is the most common type of Intercooler. Which here is cooled by the ambient air flowing through (airstream). It is advantageous to place the radiator neither in front of nor behind another radiator in order to ensure that the airflow is as free as possible. If this is not possible due to the structural conditions (Intercooler size, no space in the vehicle front ...), it should at least be the first cooler in the airstream. Cooling air ducts can also improve efficiency. The best design in terms of cooling technology is a large surface area, low cooling network depth (airflow through Intercooler is better) and a high charge air back pressure (however, if there is too much turbulence, blocking flows occur). Here is the conflict between low charge air pressure loss (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).
Air-Water Intercooler - It's a little more complicated than an Air-Air Intercooler. Because there are actually 2 coolers here. One that cools the charge air, is encased by water, and the corresponding separate water cooler in the front of the vehicle installed (usually smaller than Air-Air Intercooler). The circulation of the water is created by an electric pump. For short full load runs (1/4 mile), there are also related dry ice air heat pumps, which have an extremely high efficiency in racing operation and, like the air/water heat pumps, also contribute to a very short charge air line (fast response behaviour).
Exhaust gas temperature
This is with a turbo gasoline engine at 850°C to about 950°C under full load, can be higher for a short time (depending upon tuning), should remain however below 1050°C, otherwise with high probability a too lean mixture is present. For turbo engines, the temperature should be measured in or near the turbo (if possible before).
It is subjected to a higher thermal load in the turbo engine than in the naturally aspirated engine. On the one hand, it is subjected to higher back pressure up to the turbine and, on the other hand, it has to absorb the weight of the turbo and, if necessary, the waste gate. As a result, the manifold works more and needs high-quality materials (also for gaskets, screws, nuts). There are 2 ways to use the exhaust gas energy: Shock and congestion charging.
It should have as large a pipe diameter as possible, silencers without large constrictions and few but generous bends, because the turbine lives from the temperature gradient, which is naturally higher with less exhaust back pressure. In terms of noise behaviour, the turbo engine is more advantageous than a naturally aspirated engine, because the turbine absorbs part of the noise and acts like a silencer.
In the interest of high performance, a metal catalyst should be used for a turbocharged engine, as this has larger cross-sections in the honeycomb structure than ceramic catalysts. This helps to reduce the back pressure in the exhaust system.
They should not have any chambers or constrictions, especially at high charging pressures, as this leads to increased dynamic pressure, which has a negative effect on the performance of the turbocharger. During turbo operation, the exhaust system should be as large as possible in the interest of high performance. And be equipped with generous radii.
Engine and cylinder head
To make it resistant to the increased temperatures and pressures, the following options are available: high-quality bearings for connecting rods and crankshafts, connecting rods, pistons, stronger valve springs, pins/screws for connecting rods, pistons, cylinder heads, a nitrided crankshaft and a stable cylinder head gasket. Occasionally even diesel blocks / crankshafts (1.8 l petrol / 1.9 l diesel ...) can be used, since these are designed for higher combustion pressures. The increased temperatures are counteracted by additional oil coolers, additional water coolers, oil spray cooling of the piston heads, sodium-cooled outlet valves, increased speed and earlier switch-on point of the fans.
The compression ratio determines economy, performance at certain boost pressures, turbo lag, required fuel octane rating 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. The usual ratio is 7 to 8.5:1.
Compression reduction by means of an intermediate plate is the simplest method of reducing the compression ratio to a turbo-customary level, whereby the other engine components are usually retained. On the VR6, for example, a spacer sleeve for the chain tensioner must be used. The control times are also shifted in the early direction. When increasing the performance of turbo engines with low compressions, a further reduction is achieved by thicker cylinder head gaskets.
Cylinder head machining
She shouldn't be too strong. If possible, however, only a smoothing or very slight channel expansion should be carried out in the outlet channels. The combustion chambers and inlet ducts can be "treated" more generously. However, due to the higher temperatures and pressures during turbo operation, a little less machining should be done here as well. Great attention should be paid to the transitions from intake manifold cylinder head, cylinder head exhaust manifold and exhaust manifold loader. In professional machining, seat rings for valves and their shafts are also enlarged. Modified valves required.
Sodium cooled exhaust valves
They are a possibility to take into account the increased temperatures of a turbo engine and are present in almost all standard turbocharged engines. While the intake valves (300 to 500°C) are still relatively well cooled by the incoming gases, the exhaust valves (up to 700°C) are much more heated by the exhaust gases. The temperatures can be reduced by about 100°C due to the sodium filling.
Extremely "sharp" camshaft with long opening times and long valve strokes are not necessary for a turbo engine to achieve high performance in contrast to a suction unit, as they can cause a high proportion of the exhaust gas to return to the combustion chamber due to the high pressure in the manifold.