Chapter 7- Intake and Exhaust Systems-Automotive Engine Repair and Rebuilding

Lesson
Materials

 

Intake and Exhaust Systems

 

Introduction

It’s very simple—the better an engine can breathe, the more power it will make. The intake and exhaust system is the breathing apparatus for the engine. To maximize volumetric efficiency, the intake and exhaust manifolds must be carefully designed. Both must allow adequate airflow to provide strong engine operation. A plugged air filter can seriously restrict airflow, causing the engine to run with reduced power or even not to start. A restricted exhaust system can cause the same symptoms. The engine must be able to freely take air in and easily push air out to breathe well. The intake system must be well sealed so that a strong vacuum is formed. This ensures that air will flow into the cylinder when the throttle and intake valves are open.

Some engines used a forced induction system to increase airflow into the engine. A turbocharger or supercharger pressurizes the air above atmospheric pressure to force more air in when the intake valves open. This improvement in volumetric efficiency can increase engine power dramatically.

7-1Air Induction System

The intake system consists of the air inlet tube, an air filter, ducting, a throttle bore, and the intake manifold (Figure 7-1). The opening and closing of the throttle plate in the throttle bore controls airflow into the engine. Think of the throttle plate in a gasoline engine as a restrictive device that limits and controls the amount of air that will enter the engine. Some systems use a throttle cable to open and close the throttle plate, while others employ “drive by wire” technology. In these systems, the Powertrain Control Module (PCM) responds to an input from the apps (accelerator pedal position sensors) and controls a motor at the throttle plate to open it to the correct angle. The intake system should provide airflow at a high velocity and low volume when the engine is operating at low rpms. This ensures good fuel atomization and mixing when the injector sprays into the airstream in the manifold near the intake valve. The intake system should deliver a high volume of air when the engine is running at high rpms, to fill the combustion chamber as much as possible in a short time. This keeps power output high even at higher engine speeds. Volumetric efficiency will naturally fall at higher rpms, but the design of the intake and exhaust systems can reduce the losses.

 Figure 7-1

A late-model intake air distribution system.

The throttle position sensor is located on the throttle body, which is affixed to an intake duct. The intake duct connects to a resonator. From the resonator, air flows through the air-flow sensor and into the air cleaner assembly, which contains an air-temperature sensor.

The intake system pulls in fresh air from outside the engine compartment. Ducts direct this air through the air filter and into the throttle body assembly to power the engine. The air filter is placed below the top of the engine to allow for aerodynamic body designs. Electronic sensors measure airflow, temperature, and density. The air induction system performs the following functions:

  • Filters the air to protect the engine from wear

  • Silences air intake noise

  • Heats or cools the air as required

  • Provides the air the engine needs to operate

  • Monitors airflow temperature and density for more efficient combustion and a reduction of hydrocarbon (HC) and carbon monoxide (CO) emissions

  • Operates with the positive crankcase ventilation (PCV) system to burn the crankcase fumes in the engine

  • 7-2 Air Intake Ductwork

    Ductwork is used to direct the air into the throttle body. Cool outside air is drawn into the air cleaner assembly, and on some engines, warm air from around the exhaust is also brought in for cold engine operation. Many air ducts include a resonator chamber that looks like an irregularly shaped protrusion on the side of an intake duct. This is used to reduce the rumble of intake air as it rushes through the ductwork. Air then flows through the air filter, where particulate matter that could damage the engine is removed. Another leg of ducting connects the air filter housing to the throttle bore. Many vehicles have a mass airflow (MAF) sensor in this ducting to measure the mass of air flowing into the engine. Most engines also use an intake air temperature (IAT) sensor in the air cleaner housing of intake ductwork (Figure 7-2). As the air temperature increases, the air density decreases. The PCM will reduce the amount of fuel delivered, as needed to ensure excellent fuel economy and low emissions.

     Figure 7-2

    The intake air temperature sensor helps the PCM determine the correct fuel delivery and spark timing.

    The intake air temperature sensor helps the PCM determine the correct fuel delivery and spark timing.

    Be sure that the intake ductwork is properly installed and all connections are airtight, especially those between the MAF sensor or remote air cleaner and the throttle plate assembly. If outside air can sneak in through a leak in the ductwork, it is not filtered. Vehicles that use a MAF sensor measure the air coming into the engine from the air filter. The PCM uses this input as the primary indicator of how much fuel should be injected. If air is drawn into the engine beyond the MAF sensor through a leak in the duct, it will not be measured. The PCM will deliver less fuel, and the engine will run too lean. Generally, metal or plastic air ducts are used when engine heat is not a problem. Special paper/metal ducts are used when they will be exposed to high engine temperatures.

    7-3 Air Cleaner/Filter

    The primary function of the air filter is to prevent airborne contaminants and abrasives from entering the engine. Without proper filtration, these contaminants can cause serious damage and appreciably shorten engine life. All incoming air should pass through the filter element before entering the engine (Figure 7-3).

      Figure 7-3

    The air filter is located in the air filter housing within the intake ductwork.

    A mass airflow sensor and an air filter restriction indicator are located on the intake duct. Air flows from the duct to the air filter.

    7-3a Air Filter Design

    Air filters are basically assemblies of pleated paper supported by a layer of fine mesh wire screen. The screen gives the paper some strength and also filters out large particles of dirt. A thick plastic-like gasket material normally surrounds the ends of the filter. This gasket adds strength to the filter and serves to seal the filter in its housing. If the filter does not seal well in the housing, dirt and dust can be pulled into the airstream to the cylinders. In most air filters, the air flows from the outside of the element to the inside as it enters the intake system.

    The shape and size of the air filter element depends on its housing; the filter must be the correct size for the housing or dirt will be drawn into the engine (Figure 7-4). On today’s engines, air filters are either flat (Figure 7-5) or round (Figure 7-6). Air filters must be properly aligned and closed around the filter to ensure good airflow of clean air.

     Figure 7-4

    The air cleaner assembly is shaped to fit in the crowded engine compartment.

    The air cleaner assembly is shaped to fit in the crowded engine compartment. Figure 7-5

    Typical flat air cleaner element.

    Typical flat air cleaner element. Figure 7-6

    Typical round air filter for a late-model vehicle.

    Typical round air filter for a late-model vehicle.

    Some air cleaners have an airflow restriction indicatormounted in the air cleaner housing (refer to Figure 7-7). If the air filter element is not restricted, a window in the side of the restriction indicator shows a green color (or it may be clear). When the air filter element is restricted, the window in the airflow restriction indicator is orange and the words “Change Air Filter” appears. The air filter must then be replaced. After the air filter is replaced, a reset button on top of the airflow restriction indicator must be pressed to reset the indicator so it displays green in the window.

     Figure 7-7

    Airflow restriction indicator.

    An airflow restriction indicator has a reset button at the top, a window in the middle with a change air filter, and the service level at the base.

    Some air cleaners have a combined MAF sensor and intake air temperature (IAT) sensor attached to the air outlet on the air cleaner housing. A duct is connected from the MAF sensor to the throttle body. The MAF sensor must be attached to the air cleaner so air flows through this sensor in the direction of the arrow on the sensor housing (Figure 7-8). If the airflow is reversed through the MAF sensor, the powertrain control module (PCM) supplies a rich air-fuel ratio and increased fuel consumption. Other air cleaners contain a separated IAT sensor (Figure 7-9).

     Figure 7-8

    The mass airflow sensor must be installed in the proper direction.

    The arrow on the M Ay F sensor body indicates the direction of airflow. Figure 7-9

    The intake air temperature sensor may be mounted in the air cleaner housing.

    The intake air temperature sensor may be mounted in the air cleaner housing.

    7-4 Intake Manifold

    The intake manifold distributes the clean air as evenly as possible to each cylinder of the engine. Fuel is injected at the very end of the intake manifold runners near the combustion chamber.

    Modern intake manifolds for engines with port fuel injection are typically made of die-cast aluminum or plastic (Figure 7-10). These materials are used to reduce engine weight. A plastic manifold transfers less heat to the intake air, and this results in a denser air-fuel mixture. Plastic manifolds are also lower in cost to produce and transfer less vibration, making them quieter. Because intake manifolds for port-injected engines only deliver air to the cylinders, fuel vaporization and condensation are not design considerations. These intake manifolds deliver air to the intake ports, where it is mixed with the fuel delivered by the injectors (Figure 7-11). A primary consideration of these manifolds is the delivery of equal amounts of air to each cylinder.

     Figure 7-10

    This die-cast aluminum manifold feeds the five-cylinder engine through short runners off of the plenum.

    This die-cast aluminum manifold feeds the five-cylinder engine through short runners off of the plenum. Figure 7-11

    In a port fuel injection engine, the intake manifold delivers air to the intake ports.

    In a port fuel injection engine, the intake manifold delivers air to the intake ports.

    Intake manifolds also serve as the mounting point for many intake-related accessories and sensors. Some include a provision for mounting the thermostat and thermostat housing. In addition, connections to the intake manifold can provide a vacuum source for the exhaust gas recirculation (EGR) system, automatic transmission vacuum modulators, power brakes, and/or heater and air-conditioning airflow control doors. Many of these vacuum-operated devices are found only on older vehicles. On modern vehicles they are electronically controlled. When you compare an older engine to a modern one, one of the first things you will notice is the absence of many vacuum-controlled components that would operate from the intake manifold’s vacuum. Other devices located on or connected to the intake manifold include the manifold absolute pressure (MAP) sensor, knock sensor, various temperature sensors, and EGR passages.

    Most engines cannot produce the amount of power they should at high speeds, because they do not receive enough air. This is the reason why many race cars have hood scoops. With today’s body styles, hood scoops are not desirable, because they increase aerodynamic drag. However, to get high performance out of high-performance engines, more air must be delivered to the cylinders at high engine speeds. There are a number of ways to do this; increasing the air delivered by the intake manifold is one of them.

    7-5 Intake Manifold Tuning

    A PCM-operated electric solenoid-type valve that opens and closes some of the intake manifold runners may be called an intake manifold tuning valve (IMTV).

    Intake manifolds can be designed to improve the volumetric efficiency of the engine. This process is called intake manifold tuning. As the air rushes through the intake manifold into the cylinders, the opening and closing of the intake valves cause the airflow to pulse. If the intake manifold is divided into individual runners for each cylinder, the pulsing effect of the airflow pushes or rams more air into the cylinder. By adjusting or tuning the length of the individual runners, the manufacturer can design an intake manifold to supply the amount of air required by the particular engine. Smaller diameter, longer intake manifold runners ram more air into the cylinders at lower engine rpm. To push more air into the cylinders at higher rpm when air pulsing is faster, the intake manifold runners are designed larger in diameter and shorter. Runners must be curved to avoid sharp bends that create more airflow restriction.

    Manufacturers have also developed manifolds that deliver more air only at high engine speeds. The design of manifolds is intended to keep air moving quickly. At low rpm, narrower diameter, longer runners keep the smaller volume of air moving quicker. At high rpm, shorter, wider runners offer less restriction and allow the air to keep moving quickly.

    One such system (Figure 7-12) uses a variable-length intake manifold. At low speeds, the air travels through only part of the manifold on its way to the cylinders. When the engine speed reaches about 3,700 rpm, two butterfly valves open, forcing the air to take a longer route to the intake port. This increases the speed of the airflow, as well as increasing the amount of air available for the cylinders. As a result, more power is available at high speeds without decreasing low-speed torque and fuel economy and without increased exhaust emissions.

     Figure 7-12

    A variable-length intake manifold.

    The tubes in the intake manifold are coiled. When the runner valve is open, air flows only through the outer tube of the intake manifold. When the valve is closed, air flows through the inner tube then through the outer tube.

    Another approach is the use of two large intake manifold runners for each cylinder (Figure 7-13). Separating the intake runners from the intake ports is an assembly that has two bores for each cylinder. There is one bore for each runner. Both bores are open when the engine is running at high speeds. However, a butterfly valve in one set of the runners is closed by the PCM when the engine is operating at lower speeds. This action decreases airflow speed and volume at lower engine speeds and allows for greater airflow at high engine speeds. The butterfly valves in the intake manifold runners may be operated by a vacuum actuator, and the PCM operates an electric/vacuum solenoid that turns the vacuum on and off to the actuator. In other intake manifolds, the valves that open and close some of the runners are operated electrically by the PCM, much like a solenoid (Figure 7-14).

     Figure 7-13

    This manifold provides a short and a long runner for each cylinder. Both are opened at higher engine rpms to improve engine breathing.

    This manifold provides a short and a long runner for each cylinder. Both are opened at higher engine rpms to improve engine breathing. Figure 7-14

    The butterfly valves are controlled by the PCM through a vacuum actuator to open the second set of runners at high rpms.

    The intake manifold, consisting of a short and a long runner, is located above the engines. Butterfly valves regulate airflow into the engine, and are controlled by the vacuum actuator intake manifold runner controls, or I M R C’s, located on the sides of the engine.

    Combining a variable intake manifold with a variable valve timing system will increase the power output of a vehicle significantly. In many cases it will also reduce the emissions output and make the engine more efficient. Many vehicles produced today have such a combination of systems.

    7-6 Vacuum Basics

    Vacuum refers to any pressure that is lower than the earth’s atmospheric pressure at any given altitude. Atmospheric pressure appears as zero on most pressure gauges. This does not mean there is no pressure; rather, it means the gauge is designed to read pressures greater than atmospheric pressure. All measurements taken on this type of gauge are given in pounds per square inch and should be referred to as psig (pounds per square inch gauge). Gauges and other measuring devices that include atmospheric pressure in their readings also display their measurements in psi; however, these should be referred to as psia (pounds per square inch absolute). There is a big difference between 12 psia and 12 psig. A reading of 12 psia is less than atmospheric pressure and therefore would represent a vacuum, whereas 12 psig would be approximately 26.7 psia. When referring to the pressure in the intake manifold, we use manifold absolute pressure (MAP) as the measure. MAP is a reading of absolute pressure in the manifold. The MAP reading at idle is typically 7–9 psi. Because vacuum is defined as any pressure less than atmospheric, vacuum is any pressure less than 0 psig or 14.7 psia. Remember that vacuum is simply a difference in the pressures of two areas. Vacuum is not normally measured using negative psi numbers. Vacuum had to originally be measured in a tube filled with mercury, a metal that is in its liquid state at room temperatures. The mercury would then be drawn by the vacuum up a tube, and the amount drawn up was measured in inches. Today, we do not use mercury tubes but rather a calibrated gauge that reads in inches (or millimeters) of mercury (in. Hg or mm Hg). Other units of measurement for vacuum are kilopascals and bars. Normal atmospheric pressure at sea level is about 1 bar or 100 kilopascals.

    An engine in good condition should develop 16–18 in. Hg vacuum at idle. The amount of low pressure produced by the piston during its intake stroke depends on a number of things. Basically it depends on the cylinder’s ability to form a vacuum and the intake system’s ability to fill the cylinder. When there is high vacuum (16–18 Hg [381 to 559 mm Hg]), we know the cylinder is well sealed and not enough air is entering the cylinder to fill it. At idle, the throttle plate is almost closed and nearly all airflow to the cylinders is stopped. This is why vacuum is high during idle. Because there is a correlation between throttle position and engine load, it can be said that load directly affects engine manifold vacuum. Therefore, vacuum will be high whenever there is no, or low, load on the engine.

    7-7 Vacuum Controls

    Engine manifold vacuum is used to operate and control several devices on an engine. Prior to the mid-1960s, vacuum was used only to operate the windshield wipers and a distributor vacuum advance unit. Since then, the use of vacuum has become extensive. Some emission control output devices operate on a vacuum. This vacuum is usually controlled by solenoids that are opened or closed, depending on electrical signals received from the PCM. Engine vacuum is used to control operation of certain accessories, such as air conditioner/heater systems, power brake boosters, speed-control components, automatic transmission vacuum modulators, and so on. A vacuum solenoid either blocks or flows vacuum to actuate components or control the flow of vacuum. The evaporative emissions control system and the EGR system often use electrically controlled vacuum solenoids (Figure 7-15).

     Figure 7-15

    This vacuum solenoid is controlled by the PCM and uses the pull of vacuum to draw fuel vapors into the intake manifold.

    This vacuum solenoid is controlled by the PCM and uses the pull of vacuum to draw fuel vapors into the intake manifold.

    7-8 Turbochargers

    Another method of improving volumetric efficiency and engine performance is to compress the intake air before it enters the combustion chamber. This can be accomplished through the use of a turbocharger or a supercharger. While at idle the engine still develops the same amount of vacuum; under boost the supercharger or turbocharger delivers roughly 8–15 psi of pressure above atmospheric pressure. When the throttle opens, the greater pressure difference increases airflow into the cylinders. This increases the density of the air charge in the cylinder producing more power.

    A turbocharger or supercharger changes the effective compression ratio of an engine, simply by packing in air at a pressure that is greater than atmospheric; for example, an engine that has a compression ratio of 8:1 and receives 10 pounds (69 kPa) of boost will have an effective compression ratio of 10.5:1.

    turbocharger is a blower or special fan assembly that uses the expansion of hot exhaust gases to turn a turbine and compress incoming air. In a typical car engine, a turbocharger may increase the horsepower approximately 20 percent. A typical turbocharger consists of the following components:

    • Turbine wheel

    • Shaft

    • Compressor wheel

    • Wastegate valve

    • Actuator

    • Center housing and rotating assembly (CHRA)

    7-8a Basic Operation

    The turbine wheel and the compressor wheel are mounted on a common shaft. Both wheels have fins or blades, and each wheel is encased in its own spiral-shaped housing. The shape of the housing works to control and direct the flow of the gases. The shaft is supported on bearings in the turbocharger housing. The expelled exhaust gases from the cylinders are directed through a nozzle against the blades of the turbine wheel. When engine load is high enough, there is enough exhaust gas flow to cause the turbine wheel and shaft to rotate at a high speed. This action creates a vortex flow. Since the compressor wheel is positioned on the opposite end of the shaft, the compressor wheel must rotate with the turbine wheel (Figure 7-16).

     Figure 7-16

    Exhaust gases spin the turbine wheel. The compressor wheel is connected to the turbine through a shaft and spins at the same rate to pressurize the intake charge.

    Inlet air passes through a compressor wheel. The compressed air is then directed to the engine. The exhaust gas from the engine flows in the opposite direction and hits the turbine wheel, then continues out. The turbine wheel and the compressor wheel are connected by a shaft.

    The compressor wheel is mounted in the air intake system. As the compressor wheel rotates, air is forced into the center of the wheel, where it is caught by the spinning blades and thrown outward by centrifugal force. The air leaves the turbocharger housing and enters into the intake manifold. Since most turbocharged engines are port injected, the fuel is injected into the intake ports. The rotation of the compressor wheel compresses the air and fuel in the intake manifold, creating a denser air-fuel mixture. This increased intake manifold pressure forces more air-fuel mixture into the cylinders to provide increased engine power. The turbocharger must reach a certain rpm before it begins to pressurize the intake manifold. Some turbochargers begin to pressurize the intake manifold at 1,250 engine rpm and reach full boost pressure in the intake manifold at 2,250 rpm.

    In a normally aspirated engine, air is drawn into the cylinders by the difference in pressure between the atmosphere and engine vacuum. A turbocharger pressurizes the intake charge to a point above normal atmospheric pressure. Turbo boost is the positive pressure increase created by the turbocharger.

    A Bit of History

    Turbochargers have been common in heavy-duty applications for many years, but they were not widely used in the automotive industry until the 1980s. Turbochargers had two traditional problems that prevented their wide acceptance in automotive applications. Older turbochargers had a lag, or hesitation, on low-speed acceleration, and there was the problem of bearing cooling. Engineers greatly reduced the low-speed lag by designing lighter turbine and compressor wheels with improved blade design. Water cooling combined with oil cooling provided improved bearing life. These changes made the turbocharger more suitable for automotive applications.

    Turbocharger wheels rotate at very high speeds, in excess of 100,000 rpm. Engineers design and balance the turbocharger to run in excess of 150,000 rpm, about 25 times the maximum rpm of most engines. Due to this high-speed operation, turbocharger wheel balance and bearing lubrication are very important.

    Boost Pressure Control

    If the turbocharger boost pressure is not limited, excessive intake manifold and combustion pressure can destroy engine components. Also, if the amount of boost is too high, detonation knock can occur and decrease engine output. To control the amount of boost developed in the turbocharger, most turbochargers have a wastegate diaphragm mounted on the turbocharger. A linkage is connected from this diaphragm to a wastegate valve in the turbine wheel housing (Figure 7-17).

      Figure 7-17

    The wastegate diaphragm is operated by a PCM-controlled solenoid to protect the engine from dangerous overboosting.

    The wastegate diaphragm is operated by a PCM-controlled solenoid, to protect the engine from dangerous overboosting.

    Under low to partial load conditions, the diaphragm spring holds the wastegate valve closed. This routes all of the exhaust gases through the turbine housing. Boost pressure from the intake manifold is also supplied to the wastegate diaphragm.

    Under full load, when the boost pressure in the intake manifold reaches the maximum safe limit, the boost pressure pushes the wastegate diaphragm and opens the wastegate valve. This action allows some exhaust to bypass the turbine wheel, which limits turbocharger shaft rpm and boost pressure (Figure 7-18).

     Figure 7-18

    As boost pressure increases toward the safe limit, the wastegate opens to divert exhaust gases away from the turbine wheel.

    Inlet air passes through the intake manifold and compressor wheel and is then directed to the engine; a pipe extending from the upper pipe between the compressor and engine registers manifold pressure. Exhaust gas from the engine flows in the opposite, and hits the turbine wheel. As boost pressure in the pipe between the compressor and engine increases toward the safe limit, the waste-gate opens, to allow exhaust gas to bypass the turbine wheel. The waste-gate connects via a rod to the pipe with manifold pressure.

    On some engines, the boost pressure supplied to the wastegate diaphragm is controlled by a computer-operated solenoid. In many systems, the PCM pulses the wastegate solenoid on and off to control boost pressure. Some computers are programed to momentarily allow a higher boost pressure on sudden acceleration to improve engine performance.

    7-8b Turbo Lag

    Turbo lag occurs when the turbocharger compressor and turbine wheels are not spinning fast enough to create boost. It takes time to get the exhaust gases to bring the turbocharger wheels up to operating speed. The size and weight of the turbine and compression wheels, along with housing design, are factors that affect the amount of turbo lag. Smaller, lighter turbochargers result in less lag time but lower boost pressures. Some engines use two sequential turbochargers: a very small, lightweight one to help acceleration at low rpms and a bigger volume one to create plenty of boost to maximize power at higher rpms. Low-pressure turbochargers may provide boost of only 4–8 psi, but they reduce the lag time until the 8–15 psi from the full-size turbo kicks in. Also used on some diesel engines, variable nozzle turbine turbocharger systems have been developed to reduce the lag period (Figure 7-19).

     Figure 7-19

    Variable nozzle turbine type turbocharger.

    Variable nozzle turbine type turbocharger.

    7-8c Turbocharger Cooling

    Exhaust flow past the turbine wheel creates very high turbocharger temperature, especially under high engine load conditions. Many turbochargers have coolant lines connected from the turbocharger housing to the cooling system (Figure 7-20). Coolant circulation through the turbocharger housing helps cool the bearings and shaft. Full oil pressure is supplied from the main oil gallery to the turbocharger bearings and shaft to lubricate and cool the bearings. This oil is drained from the turbocharger housing back into the crankcase. Seals on the turbocharger shaft prevent oil leaks into the compressor or turbine wheel housings. Worn turbocharger seals allow oil into the compressor or turbine wheel housings, resulting in blue smoke in the exhaust and oil consumption. Some heat is also dissipated from the turbocharger to the surrounding air.

     Figure 7-20

    A water-cooled turbocharger uses coolant to control the temperature of the bearings and the shaft.

    Water passages around the bearings connect to 2 banjo-style water fittings at the base of the engine, from which a coolant delivery tube emerges.

    Some turbochargers do not have coolant lines connected to the turbocharger housing. These units depend on oil and air cooling. On these units, if the engine is shut off immediately after heavy-load or high-speed operation, the oil may burn to some extent in the turbocharger bearings. When this action occurs, hard carbon particles, which destroy the turbocharger bearings, are created. The coolant circulation through the turbocharger housing lowers the bearing temperature to help prevent this problem. When turbochargers that depend on oil and air cooling have been operating at heavy load or high speed, idle the engine for at least one minute before shutting it off. This action will help prevent turbocharger bearing failure.

    7-8d Intercoolers

    A disadvantage of the turbocharger (and supercharger) is that it heats the incoming air. The hotter the air, the less dense it is. As the air gets hotter, fewer air molecules can enter the cylinder on each intake stroke. Also, hotter intake air leads to detonation problems. To combat these effects, many turbocharger systems use an intercooler(Figure 7-21). The intercooler is like a radiator in that it removes heat from the turbocharger system by dissipating it to the atmosphere. The intercooler can be either air cooled or water cooled (Figure 7-22). Cooling the air makes it denser, increasing the amount of oxygen content with each intake stroke. The intercooler cools the air that leaves the turbocharger at about ‍before it enters the cylinders. For every ‍ that the air is cooled, a power gain of about 1 percent is obtained. If the intercooler is capable of cooling the air by ‍, then a 10 percent power increase is obtained.

     Figure 7-21

    The intercooler cools the pressurized air to create a denser intake charge.

    The intercooler cools the pressurized air to create a denser intake charge.  Figure 7-22

    Intercoolers can be air cooled (A) or water cooled (B).

    Air from the exhaust passes through the intercooler before being fed into the intake manifold. In an air-cooled intercooler, the intercooler is exposed to the outside air. The intake air passes through the intercooler before reaching the throttle plate that is placed ahead of the engine. In a water cooled intercooler, an electric water pump connects the intercooler to the sub-radiator. The intake air passes through the intercooler before reaching the throttle plate that is placed ahead of the engine.

    7-8e Scheduled Maintenance

    Four main things will reduce the life of a turbocharger: lack of oil, oil coking, contaminants in the oil, and ingestion of foreign material through the air intake. To prevent premature turbocharger failure, engine oil and filters should be changed at the vehicle manufacturer’s recommended intervals. The engine oil level must be maintained at the specified level on the dipstick. The air cleaner element and the air intake system must be maintained in satisfactory condition. Dirt entering the engine through an air cleaner will damage the compressor wheel blades. When coolant lines are connected to the turbocharger housing, the cooling system must be maintained according to the vehicle manufacturer’s maintenance schedule to provide normal turbocharger life.

    Turbocharged engines have a lower compression ratio than a normally aspirated engine, and many parts are strengthened in a turbocharged engine because of the higher cylinder pressure. Therefore, many components in a turbocharged engine are not interchangeable with the parts in a normally aspirated engine.

    Author’s Note

    During my experience in the automotive service industry, I encountered a significant number of turbocharged engines with low boost pressure. This low boost pressure was often caused by low engine compression. Because low engine compression reduces the amount of air taken into the engine, this problem also reduces turbocharger speed and boost pressure. Therefore, when diagnosing low boost pressure, always verify the engine condition before servicing or replacing the turbocharger.

    7-9 Superchargers

    After falling into disuse for a number of years (except for racing applications), the supercharger started to reappear on automotive engines as original equipment manufacturer (OEM) in 1989 (Figure 7-23). The supercharger is belt driven from the crankshaft by a ribbed belt (Figure 7-24). A shaft is connected from the crankshaft pulley to one of the drive gears in the front supercharger housing, and the driven gear is meshed with the drive gear. The rotors inside the supercharger are attached to the two drive gears.

     Figure 7-23

    A factory-installed supercharger.

    A factory-installed supercharger. Figure 7-24

    The supercharger is driven by a belt off of the crankshaft.

    The idler pulley assembly is connected to the supercharger drive pulley by a ribbed belt, and to the crankshaft pulley by another belt. Spring tensioners are placed on the outside of the belts.

    The supercharger may be called a blower.

    The drive gear design prevents the rotors from touching; however, there is a very small clearance between the drive and driven gears. In some superchargers, the rotor shafts are supported by roller bearings on the front and needle bearings on the back. During the manufacturing process, the needle bearings are permanently lubricated. The ball bearings are lubricated by a synthetic-based, high-speed gear oil. A plug is provided for periodic checks of the front bearing lubricant. Front bearing seals prevent lubricant loss into the supercharger housing.

    In a typical car engine, a supercharger increases horsepower approximately 20 percent compared to a normally aspirated engine with the same CID; for example, the General Motors normally aspirated 1997 3800 V-6 engine is rated at 200 HP. The supercharged version of this engine is rated at 240 HP. The supercharger will operate around 10,000 to 15,000 rpm. Unlike the turbocharger, the amount of boost the supercharger produces is a function of engine rpm (not load). The advantage of the supercharger is that it will produce more torque at lower engine speeds than a turbocharger. Also, there is no lag time associated with a supercharger. The disadvantage of the supercharger is that it consumes horsepower as it is driven.

    7-9a Supercharger Operation

    While there have been a number of supercharger designs on the market over the years, the most popular is the Roots-type supercharger. The pair of three-lobed rotor vanes (Figure 7-25) in the Roots supercharger is driven by the crankshaft. The lobes force air into the intake manifold. The helical design evens out the pressure pulses in the blower and reduces noise. It was found that a 60-degree helical twist works best for equalizing the inlet and outlet volumes. Another benefit of the helical rotor design is it reduces carryback volumes—air that is carried back to the inlet side of the supercharger because of the unavoidable spaces between the meshing rotors—which represents a loss of efficiency. Many aftermarket superchargers are a centrifugal type.

     Figure 7-25

    Common design of the rotor.

    Common design of the rotor.

    To handle the higher operating temperatures imposed by supercharging, an engine oil cooler is usually built into the engine lubrication system. This water-to-oil cooler is generally mounted between the engine front cover and oil filter.

    Intake air enters the inlet plenum at the back of the supercharger, and the rotating blades pick up the air and force it out the top of the supercharger. The blades rotate in opposite directions, acting as a pump as they rotate. This pumping action pulls air through the supercharger inlet and forces the air from the outlet. There is a very small clearance between the meshed rotor lobes and between the rotor lobes and the housing (Figure 7-26).

     Figure 7-26

    As the rotors mesh, they pump air out under pressure.

    As the two three-lobed rotor vanes turn, P S I developing, boost pressure is pushed out into the intake manifold.

    Air flows through the supercharger system components in the following order:

    1. Air flows through the air cleaner and MAF sensor into the throttle body.

    2. Airflow enters the supercharger intake plenum.

    3. From the intake plenum the air flows into the rear of the supercharger housing (Figure 7-27).

    4. The compressed air flows from the supercharger to the intercooler inlet.

    5. Air leaves the intercooler and flows into the intercooler outlet tube.

    6. Air flows from the intercooler outlet tube into the intake manifold adapter.

    7. Compressed, cooled air flows through the intake manifold into the engine cylinders.

    8. If the engine is operating at idle or very low speeds, the supercharger is not required. Under this condition, airflow is bypassed from the intake manifold adapter through a butterfly valve to the supercharger inlet plenum (Figure 7-28).

     Figure 7-27

    Airflow through a supercharger.

    Airflow through a supercharger.

     Figure 7-28

    The bypass actuator can divert airflow from the intake manifold back into the supercharger plenum to reduce boost.

    Air from the throttle body passes through a tube to the supercharger and then into the intercooler. Part of the cool compressed air flows to the intake manifold adapter, while the remaining part flows through a tube into the supercharger intake tube.

    In one example, the bypass butterfly valve (Figure 7-29) is operated by an air bypass actuator diaphragm as follows:

    1. When manifold vacuum is 7 in. Hg (23.6 kPa) or higher, the bypass butterfly valve is completely open and a high percentage of the supercharger air is bypassed to the supercharger inlet.

    2. If the manifold vacuum is 3 to 7 in. Hg (10 to 23.6 kPa), the bypass butterfly valve is partially open and some supercharger air is bypassed to the supercharger inlet, while the remaining airflow is forced into the engine cylinders.

    3. When the vacuum is less than 3 in. Hg (10 kPa), the bypass butterfly valve is closed and all the supercharger airflow is forced into the engine cylinders.

     Figure 7-29

    Supercharger bypass hose and intake elbow.

    The supercharger and plenum assembly are located on the side of the engine, while the bypass valve is at the front. A bypass hose connects the bypass valve to the elbow assembly.

    On some superchargers, the pulley size causes the rotors to turn at 2.6 times the engine speed. Since supercharger speed is limited by engine speed, a supercharger wastegate is not required. Belt-driven superchargers provide instant low-speed action compared to exhaust-driven turbochargers, which may have a low-speed lag because of the brief time interval required to accelerate the turbocharger shaft. Compared to a turbocharger, a supercharger turns at much lower speeds.

    Friction between the air and the rotors heats the air as it flows through the supercharger. The intercooler dissipates heat from the air in the supercharger system to the atmosphere, creating a denser air charge. When the supercharger and the intercooler supply cooled, compressed air to the cylinders, engine power and performance are improved.

    The compression ratio in the supercharged 3.8-liter engine is 8.2:1, compared to a normally aspirated 3.8-liter engine, which has a 9.0:1 compression ratio. The following components are reinforced in the supercharged engine because of the higher cylinder pressure:

    • Engine block

    • Main bearings

    • Crankshaft bearing caps

    • Crankshaft

    • Steel crankshaft sprocket

    • Timing chain

    • Cylinder head

    • Head bolts

    • Rocker arms

    Superchargers can be enhanced with electrically operated clutches and bypass valves. These allow the same computer that controls fuel and ignition to kick the boost on and off precisely as needed. This results in far greater efficiency than a full-time supercharger.

    7-10 Exhaust System Components

    The various components of the typical exhaust system include the following:

    • Exhaust manifold

    • Exhaust pipe and seal

    • Catalytic converter

    • Muffler

    • Resonator

    • Tailpipe

    • Heat shields

    • Clamps, brackets, and hangers

    • Exhaust gas oxygen sensors

    All the parts of the system are designed to conform to the available space of the vehicle’s undercarriage and yet be a safe distance above the road.

    7-10a Exhaust Manifold

    The exhaust manifold (Figure 7-30) collects the burnt gases as they are expelled from the cylinders and directs them to the exhaust pipe. Exhaust manifolds for most vehicles are made of cast or nodular iron. Many newer vehicles have stamped, heavy-gauge sheet metal or stainless steel units.

     Figure 7-30

    An exhaust manifold for a four-cylinder engine.

    An exhaust manifold for a four-cylinder engine.

    In-line engines have one exhaust manifold. V-type engines have an exhaust manifold on each side of the engine. An exhaust manifold will have three, four, or six passages, depending on the type of engine. These passages blend into a single passage at the other end, which connects to an exhaust pipe. From that point, the flow of exhaust gases continues to the catalytic converter, muffler, and tailpipe, and then exits at the rear of the car.

    V-type engines may be equipped with a dual exhaust system that consists of two almost identical, but individual, systems in the same vehicle.

    Exhaust systems are designed for particular engine–chassis combinations. Exhaust system length, pipe size, and silencer size are used to tune the flow of gases within the exhaust system. Proper tuning of the exhaust manifold tubes can actually create a partial vacuum that helps draw exhaust gases out of the cylinder, improving volumetric efficiency. Separate, tuned exhaust headers (Figure 7-31) can also improve efficiency by preventing the exhaust flow of one cylinder from interfering with the exhaust flow of another cylinder. Cylinders next to one another may release exhaust gas at about the same time. When this happens, the pressure of the exhaust gas from one cylinder can interfere with the flow from the other cylinder. With separate headers, the cylinders are isolated from one another, interference is eliminated, and the engine breathes better. The problem of interference is especially common with V-8 engines. However, exhaust headers tend to improve the performance of all engines.

     Figure 7-31

    Engine efficiency can be improved with tuned exhaust headers.

    Engine efficiency can be improved with tuned exhaust headers.

    Exhaust manifolds may also be the attaching point for the air injection reaction (AIR) pipe (Figure 7-32). This pipe introduces cool air from the AIR system into the exhaust stream. The added air in the exhaust stream during engine warm-up helps burn excess fuel in the exhaust and heat up the catalytic converter faster. Some exhaust manifolds have provisions for the exhaust gas recirculation (EGR) pipe. This pipe takes a sample of the exhaust gases and delivers it to the EGR valve. Also, some exhaust manifolds have a tapped bore that retains the oxygen sensor (Figure 7-33).

     Figure 7-32

    AIR pipe mounting on an exhaust manifold.

    AIR pipe mounting on an exhaust manifold. Figure 7-33

    One oxygen sensor sits in this exhaust manifold. The catalytic converter mounts onto the exhaust manifold, and another oxygen sensor fits into the exhaust pipe.

    One oxygen sensor sits in this exhaust manifold. The catalytic converter mounts onto the exhaust manifold, and another oxygen sensor fits into the exhaust pipe.

    7-10b Exhaust Pipe and Seal

    The exhaust pipe is metal pipe, made of aluminized steel, stainless steel, or zinc-plated heavy gauge steel, that runs under the vehicle between the exhaust manifold and the catalytic converter (Figure 7-34).

     Figure 7-34

    The front exhaust pipe for a V-6 engine.

    The oxygen sensor affixed to the pipe before the catalytic converter. The 2 exhaust pipes from the converter end with an exhaust gasket.

    7-10dConverter Problems

    The converter is normally a trouble-free emission control device, but three things can damage it. One is leaded gasoline. Lead coats the catalyst and renders it useless. The difficulty of obtaining leaded gasoline has reduced this problem. Another is overheating. If raw fuel enters the exhaust because of a fouled spark plug or other problem, the temperature of the converter quickly increases. The heat can melt the ceramic honeycomb or pellets inside, causing a major restriction to the flow of exhaust. A plugged converter or any exhaust restriction can cause damage to the exhaust valves due to excess heat, loss of power at high speeds, or stalling after starting (if totally blocked). The last is damage or poisoning due to silicone contamination from coolant or sealant.

    7-11 Mufflers

    The muffler is a cylindrical or oval-shaped component, generally about 2 feet (0.6 meters) long, mounted in the exhaust system about midway or toward the rear of the car. Inside the muffler is a series of baffles, chambers, tubes, and holes to break up, cancel out, or silence the pressure pulsations that occur each time an exhaust valve opens.

    Two types of mufflers are commonly used on passenger vehicles (Figure 7-38). Reverse-flow mufflers change the direction of the exhaust gas flow through the inside of the unit. This is the most common type of automotive muffler. Straight-through mufflers permit exhaust gases to pass through a single tube. The tube has perforations that tend to break up pressure pulsations. They are not as quiet as the reverse-flow type.

     Figure 7-38

    (A) Reverse-flow muffler, (B) Straight-through muffler.

    Ay: In a reverse-flow muffler, the exhaust gases pass through chambers at different levels. B: In a straight-through muffler, the gases pass through single, straight chamber.

    There have been several important changes in recent years in the design of mufflers. Most of these changes have been centered at reducing weight and emissions, improving fuel economy, and simplifying assembly. These changes include the following:

      1. New materials. More and more mufflers are being made of aluminized and stainless steel. Using these materials reduces the weight of the units as well as extends their lives.

      2. Double-wall design. Retarded engine ignition timing that is used on many small cars tends to make the exhaust pulses sharper. Many cars use a double-wall exhaust pipe to better contain the sound and reduce pipe ring.

    1. Rear-mounted muffler. More and more often, the only space left under the car for the muffler is at the very rear. This means the muffler runs cooler than before and is more easily damaged by condensation in the exhaust system. This moisture, combined with nitrogen and sulfur oxides in the exhaust gas, forms acids that rot the muffler from the inside out. Many mufflers are being produced with drain holes drilled into them.

    2. Back pressure. Even a well-designed muffler will produce some back pressure in the system. Back pressure reduces an engine’s volumetric efficiency, or ability to breathe. Excessive back pressure caused by defects in a muffler or other exhaust system part can slow or stop the engine. However, a small amount of back pressure can be used intentionally to allow a slower passage of exhaust gases through the catalytic converter. This slower passage results in more complete conversion to less harmful gases. Also, no back pressure may allow intake gases to enter the exhaust.

    7-11 Mufflers

    The muffler is a cylindrical or oval-shaped component, generally about 2 feet (0.6 meters) long, mounted in the exhaust system about midway or toward the rear of the car. Inside the muffler is a series of baffles, chambers, tubes, and holes to break up, cancel out, or silence the pressure pulsations that occur each time an exhaust valve opens.

    Two types of mufflers are commonly used on passenger vehicles (Figure 7-38). Reverse-flow mufflers change the direction of the exhaust gas flow through the inside of the unit. This is the most common type of automotive muffler. Straight-through mufflers permit exhaust gases to pass through a single tube. The tube has perforations that tend to break up pressure pulsations. They are not as quiet as the reverse-flow type.

     Figure 7-38

    (A) Reverse-flow muffler, (B) Straight-through muffler.

    Ay: In a reverse-flow muffler, the exhaust gases pass through chambers at different levels. B: In a straight-through muffler, the gases pass through single, straight chamber.

    There have been several important changes in recent years in the design of mufflers. Most of these changes have been centered at reducing weight and emissions, improving fuel economy, and simplifying assembly. These changes include the following:

      1. New materials. More and more mufflers are being made of aluminized and stainless steel. Using these materials reduces the weight of the units as well as extends their lives.

      2. Double-wall design. Retarded engine ignition timing that is used on many small cars tends to make the exhaust pulses sharper. Many cars use a double-wall exhaust pipe to better contain the sound and reduce pipe ring.

    1. Rear-mounted muffler. More and more often, the only space left under the car for the muffler is at the very rear. This means the muffler runs cooler than before and is more easily damaged by condensation in the exhaust system. This moisture, combined with nitrogen and sulfur oxides in the exhaust gas, forms acids that rot the muffler from the inside out. Many mufflers are being produced with drain holes drilled into them.

    2. Back pressure. Even a well-designed muffler will produce some back pressure in the system. Back pressure reduces an engine’s volumetric efficiency, or ability to breathe. Excessive back pressure caused by defects in a muffler or other exhaust system part can slow or stop the engine. However, a small amount of back pressure can be used intentionally to allow a slower passage of exhaust gases through the catalytic converter. This slower passage results in more complete conversion to less harmful gases. Also, no back pressure may allow intake gases to enter the exhaust.

    7-11a Resonator

    On some older vehicles, there is an additional muffler, known as a resonator or silencer. This unit is designed to further reduce or change the sound level of the exhaust. It is located toward the end of the system and generally looks like a smaller, rounder version of a muffler.

    7-11b Tailpipe

    The tailpipe is the last pipe in the exhaust system. It releases the exhaust fumes into the atmosphere beyond the back end of the car.

    7-11c Heat Shields

    Heat shields are used to protect other parts from the heat of the exhaust system and the catalytic converter (Figure 7-39). They are usually made of pressed or perforated sheet metal. Heat shields trap the heat in the exhaust system, which has a direct effect on maintaining exhaust gas velocity.

     Figure 7-39

    Typical locations of heat shields in an exhaust system.

    A heat insulator is affixed to the catalytic converter of the exhaust system. On either side of the converter, which is covered with a heat shield, there are H O 2 S sensors. The upstream sensor, closer to the gasket, is used for fuel control, and the downstream one is used for catalyst testing. Heat insulators are also placed on the resonator and muffler.A Bit of History

    In the 1930s Charles Nelson Pogue developed the Pogue carburetor. This carburetor used exhaust heat to vaporize the fuel before it was mixed with the air entering the engine. Charles Pogue was issued several patents on this carburetor and claimed greatly increased fuel mileage. Mr. Pogue never did sell his invention to any of the car manufacturers, but rumors were repeated for years about the fantastic fuel economy supplied by this carburetor.

    7-11d Clamps, Brackets, and Hangers

    Clamps, brackets, and hangers are used to properly join and support the various parts of the exhaust system. These parts also help isolate exhaust noise by preventing its transfer through the frame (Figure 7-40) or body to the passenger compartment. Clamps help secure exhaust system parts to one another. The pipes are formed in such a way that one slips inside the other. This design makes a close fit. A U-type clamp usually holds this connection tight (Figure 7-41). Another important job of clamps and brackets is to hold pipes to the bottom of the vehicle. Clamps and brackets must be designed to allow the exhaust system to vibrate without transferring the vibrations through the car.

     Figure 7-40

    Rubber hangers are used to keep the exhaust system in place without allowing it to contact the frame.

    Rubber hangers are used to keep the exhaust system in place without allowing it to contact the frame. Figure 7-41

    A U-clamp is often used to secure two pipes that slip together.

    A U-bolt is placed around the two pipes that slip together, one inside the other. A clamp is secured to the ends of the U-bolt with nuts.

    Many different types of flexible hangers are available. Each is designed for a particular application. Some exhaust systems are supported by doughnut-shaped rubber rings between hooks on the exhaust component and on the frame or car body. Others are supported at the exhaust pipe and tailpipe connections by a combination of metal and reinforced fabric hanger. Both the doughnuts and the reinforced fabric allow the exhaust system to vibrate or move without breakage that could be caused by direct physical connection to the vehicle’s frame.

    Some exhaust systems are a single unit in which the pieces are welded together by the factory. By welding instead of clamping the assembly together, car makers save the weight of overlapping joints as well as that of clamps.

    Author’s Note

    During my experience in the automotive service industry, I encountered several cases where restricted exhaust or intake systems were misdiagnosed and confused with ignition system or fuel system defects. Defective fuel system or ignition system components may cause a loss of engine power and reduced maximum speed, but these symptoms are accompanied by cylinder misfiring, engine surging, or both. When the exhaust or intake system is restricted, the maximum speed is reduced, but the engine does not misfire or surge.

    Chapter Review

    7-12a Summary

      • The air induction system allows a controlled amount of clean, filtered air to enter the engine. Cool air is drawn in through a fresh air tube. It passes through an air cleaner before entering the throttle body.

      • The air intake ductwork conducts airflow from the remote air cleaner to the throttle body mounted on the intake manifold.

      • The air cleaner/filter removes dirt particles from the air flowing into the intake manifold, to prevent these particles from causing engine damage.

      • The intake manifold distributes the air or air-fuel mixture as evenly as possible to each cylinder. Intake manifolds are made of cast iron, plastic, or die-cast aluminum.

    • The vacuum in the intake manifold operates many systems such as emission controls, brake boosters, heater/air conditioner, cruise controls, and more. A diagram of emission system vacuum hose routing is located on the underhood decal. Loss of vacuum can create many drivability problems.

    • Turbochargers and superchargers create forced induction systems that improve the volumetric efficiency and power of the engine.

    • Turbochargers use the heat energy in exhaust gases to spin the turbine and pressurize intake air on the compressor side.

    • A turbocharger wastegate regulates boost pressure based on engine load to prevent engine-damaging overboost conditions.

    • A belt-driven supercharger supplies air to the intake manifold under pressure to increase engine power.

    • A vehicle’s exhaust system carries away gases from the passenger compartment, cleans the exhaust emissions, and muffles the sound of the engine. Its components include the exhaust manifold, exhaust pipe, catalytic converter, muffler, resonator, tailpipe, heat shields, clamps, brackets, and hangers.

    • The exhaust manifold is a bank of pipes that collects the burned gases as they are expelled from the cylinders and directs them to the exhaust pipe.

    • The catalytic converter reduces HC, CO, NOx and emissions.

    • The muffler consists of a series of baffles, chambers, tubes, and holes to break up, cancel out, and silence pressure pulsate

Chapter Review

7-12bReview Questions

Short-Answer Essays

  1. Explain the operation of an airflow restriction indicator.
  2. Explain the purposes of the intake manifold.
  3. Explain the advantages of plastic intake manifolds.
  4. Explain the operation of an intake manifold with dual runners at low and high engine speeds.
  5. Explain how a turbocharger or supercharger creates more engine power.
  6. Describe basic turbocharger operation.
  7. What is the purpose of the intercooler?
  8. Describe the advantages of tuned exhaust manifolds compared to conventional exhaust manifolds.
  9. Explain two catalytic converter operating problems.
  10. When referring to a turbocharger system, describe what oil coking is, how it is caused, and how to prevent it.

Fill-in-the-Blanks

  1. Without proper intake air filtration, contaminants and abrasives in the air will cause severe ___ damage.
  2. If the air filter is restricted, the airflow restriction indicator window appears ___ in color.
  3. When an intake manifold has dual runners, both runners are open at ____ engine speeds.
  4. The exhaust flows over the ____ wheel in a turbocharger.
  5. Turbocharged or supercharged engines have ____ compression ratios compared to naturally aspirated engines.
  6. The air flows through the intercooler ____ it flows through the supercharger.
  7. In place of cast- or nodular-iron exhaust manifolds, newer vehicles have manifolds manufactured from stamped, heavy-gauge sheet metal or___ ___  .
  8. A tuned exhaust manifold prevents exhaust flow from one cylinder from interfering with the ___ ____  from another cylinder.
  9. A catalytic converter may be overheated by a(n)____  air-fuel ratio.
  10. The exhaust pipe between the engine and the catalytic converter may be a ____ ____  design in order to be quieter.

Multiple Choice

  1. The intake manifold is typically made of.
    1. plastic.
    2. stainless steel.
    3. cast iron.
    4. fiber composites.
  2. An engine should develop____  in. Hg vacuum at idle.
    1. 5
    2. 8
    3. 18
    4. 25
  3. A variable-length intake manifold is designed to increase.
    1. compression.
    2. airflow at idle.
    3. intake turbulence.
    4. airflow at high rpm.
  4. The catalytic converter reduces  emissions.
    1. HC,CO2 , O2
    2. HC, CO, NOx
    3. CO,CO2 , NOx
    4. N, HC, O2
  5. Technician A says that a turbocharger may spin at speeds of 100,000 rpm.Technician B says that oil coking is a common cause of turbocharger failure.Who is correct?
    1. A only
    2. B only
    3. Both A and B
    4. Neither A nor B
  6. On a turbocharged engine, when the opens, boost pressure is reduced.
    1. Compressor bypass
    2. Turbine dump valve
    3. Wastegate
    4. Intercooler router
  7. A supercharger typically uses  to pressurize the intake charge.
    1. two rotors
    2. four rotors
    3. a compressor pump
    4. three helix gears
  8. A mini-converter is used.
    1. on small engines where a normal converter will not fit properly.
    2. on engines that used leaded fuels.
    3. in conjunction with EGR systems to supply clean exhaust for the cylinders.
    4. to reduce emissions during engine warm-up.
  9. A restricted exhaust system can cause.
    1. stalling.
    2. backfiring.
    3. loss of power.
    4. acceleration stumbles.
  10. All of these statements about an intake manifold dual runner system are true except:
    1. Both runners to each cylinder are open at 1,400 engine rpm.
    2. The butterfly valves in one set of runners may be operated by a vacuum actuator.
    3. The butterfly valves may be operated electrically by the PCM.
    4. One runner to each cylinder is open at 900 engine rpm.

Upon completion and review of this chapter, you should understand and be able to describe:

  • The purpose of the air filter.
  • The design of the air filter.
  • The three different materials used to manufacture intake manifolds.
  • The purpose of the intake manifold.
  • The advantages of aluminum and plastic intake manifolds compared to cast iron.
  • The operation and advantages of intake manifolds with dual runners.
  • Two different methods for operating the valves that open and close the intake manifold runners.
  • How the engine creates vacuum.
  • How vacuum is used to operate and control many automotive devices.
  • The operation of exhaust system components, including exhaust manifold, gaskets, exhaust pipe and seal, muffler, resonator, and tailpipe, and clamps, brackets, and hangers.
  • The benefits and operation of turbochargers and superchargers.
  • The purpose and operation of the catalytic converter.

Introduction

It’s very simple—the better an engine can breathe, the more power it will make. The intake and exhaust system is the breathing apparatus for the engine. To maximize volumetric efficiency, the intake and exhaust manifolds must be carefully designed. Both must allow adequate airflow to provide strong engine operation. A plugged air filter can seriously restrict airflow, causing the engine to run with reduced power or even not to start. A restricted exhaust system can cause the same symptoms. The engine must be able to freely take air in and easily push air out to breathe well. The intake system must be well sealed so that a strong vacuum is formed. This ensures that air will flow into the cylinder when the throttle and intake valves are open.

Some engines used a forced induction system to increase airflow into the engine. A turbocharger or supercharger pressurizes the air above atmospheric pressure to force more air in when the intake valves open. This improvement in volumetric efficiency can increase engine power dramatically.

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