By Jim Marotta
At 100 horsepower per liter, GMβs newer turbocharged 1.4L has the power of a larger engine but retains the efficiency of a small-displacement four-cylinder in most driving conditions. Courtesy GM
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A naturally aspirated automobile engine uses the downward stroke of a piston to create an area of low pressure in order to draw air into the cylinder through the intake valves. Because the pressure in the atmosphere is no more than 14.7 psi, there is a limit to the amount of airflow entering the combustion chamber.
A turbocharged engine uses a radial fan pump driven by the engineβs exhaust that consists of a turbine and a compressor on a shared shaft. The turbine converts exhaust gases exiting the engine into rotational force, which is used to drive a compressor which draws in ambient air and pumps it at high pressure into the intake manifold to improve the engineβs volumetric efficiency. This results in a greater mass of air entering the cylinders on each intake stroke.
There are four main components to a turbocharger: the housing, the impeller/turbine wheels, the center hub and the bypass.
The size and shape of the housings fitted around the impeller and turbine affect performance,Β response, and efficiency. Courtesy Borg-Warner
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The size and shape of the housings fitted around the impeller and turbine dictate the performance characteristics of the overall turbocharger. This allows the designer of the engine system to tailor the compromises between performance, response, and efficiency to application or preference.
The impeller and turbine wheel sizes also dictate the amount of air or exhaust that can be flowed through the system. Generally, the larger the turbine and compressor wheels, the larger the flow capacity. The shape, curvature and number of blades on the wheels allow infinite variability in design to tailor a turbocharger to a given engine.
Water-cooled bearings, such as the one shown, allow engine coolant to keep the lubricating oil cooler, avoiding possible oil coking from the extreme heat found in the turbine. Courtesy Borg-Warner
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The center hub connects the compressor impeller and turbine and uses a bearing lubricated by a constant supply of pressurized engine oil. While the engine oil cools some systems, the preferred method is to use engine coolant to keep the lubricating oil cooler, avoiding possible oil coking from the extreme heat found in the turbine.
Turbos use a bypass or wastegate to prevent over-pressurizing the system. At a specific boost pressure, a bypass feeds part of the exhaust gas flow around the turbine. The wastegate which opens or closes the bypass is usually operated by a spring-loaded diaphragm in response to the boost pressure.
There are several tips to maintaining and servicing turbochargers:
Planning to service or repair your vehicle? Chilton can help! Access procedures, specifications, tips, and more at http://www.ChiltonDIY.com/.
A muscle car enthusiast and drag racer, Jim Marotta is a freelance automotive writer with more than 20 years experience in the automotive industry. |
Years ago, vehicles were equipped with carburetors and required a longer cranking time to start. In many instances this longer cranking time would reveal a weak battery. You could actually hear the cranking power reduced especially in cold weather. When fuel-injected engines became the norm this was not as evident due to the fact that the vehicle starts up quicker.
A sudden change in temperature usually takes a weak battery out. Thatβs why the day before your vehicle may have started fine, with no warning of a problem. Then an extreme change in the weather (hot or cold) causes the weak battery to die, seemingly without a warning.
Why do batteries fail?
Itβs unusual for a battery to malfunction because of a defect, driving habits are the usual cause. Using a lot of vehicle accessories and driving short distances prevents the battery from fully charging. Extended idling with heavy accessory use or driving a short distance only once a week can also reduce battery performance.
When the battery does not have have an opportunity to charge fully, acid stratification occurs. The electrolyte (battery acid) in a stratified battery concentrates on the bottom. It is similar to the way sugar granules collect on the bottom of a cup of coffee before it is stirred. Batteries tend to stratify if kept at low charge (below 80%) and donβt get the opportunity to receive a full charge. For example, short distance driving while running windshield wipers and electric heaters contributes to acid stratification. Acid stratification reduces the overall performance and life of the battery.
How to protect the battery
Check your battery every two years and keep the connections clean. Also clean the area around the battery hold down. Usually if a battery is super corroded the terminals leads are no longer airtight. If you clean your battery terminals and cables and the corrosion returns, replace the battery. If your battery is four years old and corroded, replace the battery.
Batteries can cause all kinds of crazy problems; the vehicleβs electrical system has to be 100%. I have seen people replace parts on vehicles when the only thing wrong was a weak battery.
Just recently I checked a friendβs car and found a dead battery. I explained the battery read 12.5v but would not start the vehicle. He came back and told us the battery was okay. I asked the gentleman if he load tested it. He had not, but when he did he came back with a new battery.
Batteries can be difficult to diagnose, if your battery is more than three years old, my suggestion is to replace it. If you are seeing excessive corrosion and have had problems donβt fool around with an old battery. Have it checked out.
Battery Basics
Typical automotive batteries are made of five basic components:
Keep your vehicle running smoothly with maintenance schedules, service and repair information, Technical Service Bulletins and Recalls at: ChiltonDIY.com and ChiltonPRO.com.