The vanes are controlled by a membrane identical to the one on a wastegate but the level of control required is a bit different. The Porsche Turbo has a twin turbocharged 3. This is because in petrol cars exhaust temperatures are much higher than in diesel cars , and this normally has adverse effects on the delicate, moveable vanes of the turbo.
Porsche engineers claim to have managed this problem with the new Turbo. As long as the oil supply is clean and the exhaust gas does not become overheated lean mixtures or advanced spark timing on a gasoline engine a turbocharger can be very reliable but care of the unit is important.
Replacing a turbo that lets go and sheds its blades will be expensive. The use of synthetic oils is recommended in turbo engines. After high speed operation of the engine it is important to let the engine run at idle speed for around one to three minutes before turning off the engine. For example Saab , in its owner manuals, recommends a period of just 30 seconds. This lets the turbo rotating assembly cool from the lower exhaust gas temperatures.
Not doing this will also result in the critical oil supply to the turbocharger being severed when the engine stops while the turbine housing and exhaust manifold are still very hot, leading to coking of the lubricating oil trapped in the unit when the heat soaks into the bearings and later, failure of the supply of oil when the engine is next started causing rapid bearing wear and failure.
Even small particles of burnt oil will accumulate and lead to choking the oil supply and failure. A turbo timer is a device designed to keep an automotive engine running for a pre-specified period of time, in order to execute this cool-down period automatically. Oil coking is completely eliminated by foil bearings. This problem is less pronounced with turbochargers used in diesel engines, due to the lower exhaust temperatures and generally slower engine speeds.
It is usual for the manufacturer to specify a second period of idling before switching off to ensure the turbocharger is running at its idle speed to prevent damage to the bearings when the oil supply is cut off. By installing a Turbo timer, it will allow you to set the exact time in order for the turbos to cool down. A more complex and problematic protective barrier against oil coking is the use of watercooled bearing cartridges. The water boils in the cartridge when the engine is shut off and forms a natural recirculation to drain away the heat.
It is still a good idea to not shut the engine off while the turbo and manifold are still glowing. In custom applications utilising tubular headers rather than cast iron manifolds, the need for a cooldown period is reduced because the lighter headers store much less heat than heavy cast iron manifolds. Diesel engines are usually much kinder to turbos because their exhaust gas temperature is much lower than that of gasoline engines. A lag is sometimes felt by the driver of a turbocharged vehicle as a delay between pushing on the accelerator pedal and feeling the turbo kick-in.
This is symptomatic of the time taken for the exhaust system driving the turbine to come to high pressure and for the turbine rotor to overcome its rotational inertia and reach the speed necessary to supply boost pressure. The directly-driven compressor in a positive-displacement supercharger does not suffer this problem.
Centrifugal superchargers do not build boost at low RPMs like a positive displacement supercharger will. Conversely on light loads or at low RPM a turbocharger supplies less boost and the engine is more efficient than a supercharged engine. Lag can be reduced by lowering the rotational inertia of the turbine, for example by using lighter parts to allow the spool-up to happen more quickly.
Ceramic turbines are a big help in this direction. Unfortunately, their relative fragility limits the maximum boost they can supply. Another way to reduce lag is to change the aspect ratio of the turbine by reducing the diameter and increasing the gas-flow path-length. Increasing the upper-deck air pressure and improving the wastegate response helps but there are cost increases and reliability disadvantages that car manufacturers are not happy about.
Lag is also reduced by using a foil bearing rather than a conventional oil bearing. By clipping a minute portion off the tip of each blade of the turbine wheel, less restriction is imposed upon the escaping exhaust gases. This imparts less impedance onto the flow of exhaust gases at low RPM, allowing the vehicle to retain more of its low-end torque, but also pushes the effective boost RPM to a slightly higher level.
The amount a turbine wheel is and can be clipped is highly application-specific. Turbine clipping is measured and specified in degrees. Other setups, most notably in V-type engines, utilize two identically-sized but smaller turbos, each fed by a separate set of exhaust streams from the engine. The two smaller turbos produce the same or more aggregate amount of boost as a larger single turbo, but since they are smaller they reach their optimal RPM, and thus optimal boost delivery, faster.
Such an arrangement of turbos is typically referred to as a parallel twin-turbo system. A typical arrangement for this is to have one turbo active across the entire rev range of the engine and one coming on-line at higher RPM. Early designs would have one turbocharger active up to a certain RPM, after which both turbochargers are active. Below this RPM, both exhaust and air inlet of the secondary turbo are closed. Being individually smaller they do not suffer from excessive lag and having the second turbo operating at a higher RPM range allows it to get to full rotational speed before it is required.
Regarding power, if you have enough, you have enough. Of course with turbo, you would have more and your mpg would be better. How do you reduce turbo lag? Though some turbo lag is inevitable, it's certainly possible to reduce turbo lag with a few bolt-on engine modifications. Replace your turbo vehicle's exhaust downpipe with a smaller-diameter unit.
Replace your stock blow-off valve with an aftermarket unit. Purchase a new intercooler kit for your turbo vehicle. Do turbocharged engines require more maintenance? Turbocharged engines will require more frequent oil changes and fresh spark plugs, though turbo engines typically don't require additional service compared to naturally aspirated engines. Why do turbos fail?
Undoubtedly the most common reason for turbocharger failures is the presence of problems in engine lubrication. Simply put, if you have either oil contamination or even oil starvation, then this can lead to turbo failure. This assembly is where the turbine wheels and the turbo compressor are mounted. Can you drive a turbo car without a turbo?
The vehicle can run without an efficiently functioning turbocharger, but it will perform poorly, and your decision could possibly have dramatic repercussions.
If the issue is an oil supply or internal component-related problem, complete failure is imminent. As air temperature increases the density of the air, and the amount of oxygen it holds, decreases.
This means that the turbocharger has to work harder, spin faster and compress more air to produce the same amount of boost it would at lower temperatures. Boost pressure is usually very low at idle no load condition. Turbo is turning at lower speed due to smaller volume of exhaust going thru turbo. Your highest boost will happen at full load on engine and has the most volume going thru the turbo.
A lot of engines now use a exhaust bypass to limit max boost pressure. Turbos are more efficient than superchargers thanks to lower parasitic losses but they can have lag in spinning up while they wait for exhaust pressure. Overspeeding can push the turbo beyond its safe operating parameters, causing it to fail by damaging the turbine or compressor wheels and bearings.
If the turbo continues to overspeed, it can overboost the engine, resulting in serious damage to the internal components and potentially complete engine failure. Furthermore, is a turbo always spinning?
Basically a turbo will spin at idle rpm. This website uses cookies to personalize your content including ads , and allows us to analyze our traffic. Read more about cookies here.
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