0135093899_pp10a

CHAPTER 10

Intake and Exhaust Systems

Automotive Engine Performance, 3/eBy James D. Halderman

Copyright 2010, 2007, 2003 Pearson Education, Inc.,Upper Saddle River, NJ 07458 All rights reserved.

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OBJECTIVES

After studying Chapter 10, the reader will be able to:

Prepare for ASE Engine Performance (A8) certification test content area C (Air Induction and Exhaust Systems Diagnosis and Repair).

Discuss the purpose and function of intake manifolds.

Explain the differences between throttle fuelinjection manifolds and port fuel-injection manifolds.

Describe the operation of the exhaust gas recirculation system in the intake manifold.

List the materials used in exhaust manifolds and exhaust systems.



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KEY TERMS
annealing exhaust gas recirculation (EGR)hangers Helmholtz resonator micron plenum


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AIR INTAKE FILTRATION
Gasoline must be mixed with air to form a combustible mixture.Air movement into an engine occurs due to low pressure (vacuum) being created in the engine.
FIGURE 101 Downward movement of the piston lowers the air pressure inside the combustion chamber. The pressure differential between the atmosphere and the inside of the engine forces air into the engine.



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Like gasoline, air contains dirt and other materials which cannot be allowed to reach the engine. Just as fuel filters are used to clean impurities from gasoline, an air cleaner and filter are used to remove contaminants from the air. The three main jobs of the air cleaner and filter are to:Clean the air before it is mixed with fuelSilence intake noiseAct as a flame arrester in case of a backfire


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FIGURE 102 Dust and dirt in the air are trapped in the air filter so they do not enter the engine.



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FILTER REPLACEMENTAIR FILTER ELEMENTSREMOTELY MOUNTED AIR FILTERS AND DUCTS


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FIGURE 103 Most air filter housings are located on the side of the engine compartment and use flexible rubber hose to direct the airflow into the throttle body of the engine.



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Always Check the Air Filter
Always inspect the air filter and the air intake system carefully during routine service. Debris or objects deposited by animals can cause a restriction to the airflow and can reduce engine performance.


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Always Check the Air Filter

FIGURE 104 (a) Note the discovery as the air filter housing was opened during service on a Pontiac Bonneville. The nuts were obviously deposited by squirrels (or some other animal). (b) Not only was the housing filled with nuts, but also this air filter was extremely dirty, indicating that this vehicle had not been serviced for a long time.



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What Does This Tube Do?
The tube shape is designed to dampen out certain resonant frequencies that can occur at certain engine speeds. The length and shape of this tube are designed to absorb shock waves that are created in the air intake system and to provide a reservoir for the air that will then be released into the airstream during cycles of lower pressure. This resonance tube is often called a Helmholtz resonator, named for the discoverer of the relationship between shape and value of frequency Herman L. F. von Helmholtz (18211894) of the University of Hnizsberg in East Prussia. The overall effect of these resonance tubes is to reduce the noise of the air entering the engine.


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What Does This Tube Do?

FIGURE 105 A resonance tube, called a Helmholtz resonator, is used on the intake duct between the air filter and the throttle body to reduce air intake noise during engine acceleration.



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ENGINE AIR TEMPERATURE REQUIREMENTS
Some form of thermostatic control has been used on vehicles equipped with a throttle-body fuel injection to control intake air temperature for improved driveability. In a throttle-body fuel injection system, the fuel and air are combined above the throttle plate and must travel through the intake manifold before reaching the cylinders. Air temperature control is needed under these conditions to help keep the gas and air mixture combined.


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ENGINE AIR TEMPERATURE REQUIREMENTS
Heat radiating from the exhaust manifold is retained by the heat stove and sent to the air cleaner inlet to provide heated air to the throttle body.An air control valve or damper permits the air intake of:Heated air from the heat stoveCooler air from the snorkel or cold-air ductA combination of both


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THROTTLE-BODY INJECTION INTAKE MANIFOLDS
The intake manifold is also called the inlet manifold. Smooth operation can only occur when each combustion chamber produces the same pressure as every other chamber in the engine.For this to be achieved, each cylinder must receive a charge exactly like the charge going into the other cylinders in quality and quantity.


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The charges must have the same physical properties and the same airfuel mixture.A throttle-body fuel injector forces finely divided droplets of liquid fuel into the incoming air to form a combustible airfuel mixture.
FIGURE 106 A throttle-body injection (TBI) unit used on a GM V-6 engine.



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FIGURE 107 Heavy fuel droplets separate as they flow around an abrupt bend in an intake manifold.



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Check the Intake If an Exhaust Noise
Because many V-type engines equipped with a throttle-body injection and/or EGR valve use a crossover exhaust passage, a leak around this passage will create an exhaust leak and noise. Always check for evidence of an exhaust leak around the intake manifold whenever diagnosing an exhaust sound.


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PORT FUEL-INJECTION INTAKE MANIFOLDS
The size and shape of port fuel-injected engine intake manifolds can be optimized because the only thing in the manifold is air.The fuel injection is located in the intake manifold about 3 to 4 inches (70 to 100 mm) from the intake valve. Therefore, the runner length and shape are designed for tuning only. There is no need to keep an airfuel mixture homogenized throughout its trip from the TBI unit to the intake valve. Typically, long runners build low-RPM torque while shorter runners provide maximum high-RPM power.


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FIGURE 108 The graph shows the effect of sonic tuning of the intake manifold runners. The longer runners increase the torque peak and move it to a lower RPM. The 600-mm-long intake runner is about 24 inches long.



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FIGURE 109 Airflow through the large diameter upper intake manifold is distributed to smaller diameter individual runners in the lower manifold in this two-piece manifold design.



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VARIABLE INTAKES
Many intake manifolds are designed to provide both short runners, best for higher engine speed power, and longer runners, best for lower engine speed torque. The valve(s) that control the flow of air through the passages of the intake manifold are computer controlled.
FIGURE 1010 The air flowing into the engine can be directed through long or short runners for best performance and fuel economy.



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PLASTIC INTAKE MANIFOLDS
Most thermoplastic intake manifolds are molded from fiberglassreinforced nylon. The plastic manifolds can be cast or injection molded. Some manifolds are molded in two parts and bonded together. Plastic intake manifolds are lighter than aluminum manifolds and can better insulate engine heat from the fuel injectors.Plastic intake manifolds have smoother interior surfaces than do other types of manifolds, resulting in greater airflow.


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PLASTIC INTAKE MANIFOLDS

FIGURE 1011 Many plastic intake manifolds are constructed using many parts glued together to form complex passages for airflow into the engine.



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EXHAUST GAS RECIRCULATION PASSAGES
To reduce the emission of oxides of nitrogen (NOx), engines have been equipped with exhaust gas recirculation (EGR) valves. From 1973 until recently, they were used on almost all vehicles. Because of the efficiency of computer-controlled fuel injection, some newer engines do not require an EGR system to meet emission standards. Some engines use intake and exhaust valve overlap as a means of trapping some exhaust in the cylinder as an alternative to using an EGR valve.


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EXHAUST GAS RECIRCULATION PASSAGES

FIGURE 1012 The exhaust gas recirculation system is more efficient at controlling NOx emissions if the exhaust gases are cooled. A long metal tube between the exhaust manifold and the intake manifold allows the exhaust gases to cool before entering the engine.



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UPPER AND LOWER INTAKE MANIFOLDS
Many intake manifolds are constructed in two parts.A lower section attaches to the cylinder heads and includes passages from the intake ports.An upper manifold, also called the plenum, connects to the lower unit and includes the long passages needed to help provide the ram effect that helps the engine deliver maximum torque at low engine speeds. The throttle body attaches to the upper intake.


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EXHAUST MANIFOLD DESIGN
The exhaust manifold is designed to collect high-temperature spent gases from the head exhaust ports.
FIGURE 1013 The exhaust gases are pushed out of the cylinder by the piston on the exhaust stroke.



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FIGURE 1014 This exhaust manifold has a heat shield to help retain the heat and help reduce exhaust emissions.



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FIGURE 1015 Many exhaust manifolds are constructed of pressed steel and are free flowing to improve engine performance.



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EXHAUST MANIFOLD GASKETS
Exhaust manifold gaskets are included in gasket sets to seal slightly warped exhaust manifolds. These gaskets should be used, even if the engine did not originally use exhaust manifold gaskets. When a perforated core exhaust manifold gasket has facing on one side only, put the facing side against the head and put the manifold against the perforated metal core. The manifold can slide on the metal of the gasket just as it slid on the sealing surface of the head.


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How Can a Cracked Exhaust Manifold Affect Engine Performance?
A crack in an exhaust manifold will not only allow exhaust gases to escape and cause noise but the crack can also allow air to enter the exhaust manifold.


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How Can a Cracked Exhaust Manifold Affect Engine Performance?

FIGURE 1016 A crack in an exhaust manifold is often not this visible. A crack in the exhaust manifold upstream of the oxygen sensor can fool the sensor and affect engine operation.



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EXHAUST MANIFOLD GASKETS

FIGURE 1017 Typical exhaust manifold gaskets. Note how they are laminated to allow the exhaust manifold to expand and contract due to heating and cooling.



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The Correct Tools Save Time
When cast-iron exhaust manifolds are removed, the stresses built up in the manifolds often cause the manifolds to twist or bend. This distortion even occurs when the exhaust manifolds have been allowed to cool before removal. Attempting to reinstall distorted exhaust manifolds is often a timeconsuming and frustrating exercise.However, special spreading jacks can be used to force the manifold back into position so that the fasteners can be lined up with the cylinder head.


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The Correct Tools Save Time

FIGURE 1018 An exhaust manifold spreader tool is a tool that is absolutely necessary to use when reinstalling exhaust manifolds. When they are removed from the engine, they tend to warp slightly even though the engine is allowed to cool before being removed. The spreader tool allows the technician to line up the bolt holes without doing any harm to the manifold.



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MUFFLERS
Sound is air vibration. When the vibrations are large, the sound is loud. The muffler catches the large bursts of highpressure exhaust gas from the cylinder, smoothing out the pressure pulses and allowing them to be released at an even and constant rate. It does this through the use of perforated tubes within the muffler chamber. The smooth-flowing gases are released to the tailpipe. In this way, the muffler silences engine exhaust noise.


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MUFFLERS

FIGURE 1019 Exhaust gases expand and cool as they travel through the passages in the muffler.



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Why Is There a Hole in My Muffler?
Many mufflers are equipped with a small hole in the lower rear part to drain accumulated water. About 1 gallon of water is produced in the form of steam for each gallon of gasoline burned. The water vapor often condenses on the cooler surfaces of the exhaust system unless the vehicle has been driven long enough to fully warm the muffler above the boiling point of water (212F [100C]).


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Why Is There a Hole in My Muffler?

FIGURE 1020 A hole in the muffler allows condensed water to escape.



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More Airflow More Power
One of the most popular high-performance modifications is to replace the factory exhaust system with a low-restriction design and to replace the original air filter and air filter housing with a low-restriction unit.The installation of an aftermarket air filter not only increases power, but also increases air induction noise, which many drivers prefer. The aftermarket filter housing, however, may not be able to effectively prevent water from being drawn into the engine if the vehicle is traveling through deep water.


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Almost every modification that increases performance has a negative effect on some other part of the vehicle, or else the manufacturer would include the change at the factory.


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FIGURE 1021 A high-performance aftermarket air filter often can increase airflow into the engine for more power.



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SUMMARY

All air entering an engine must be filtered.

Engines that use throttle-body injection units are equipped with intake manifolds that keep the airflow speed through the manifold at 50 to 300 feet per second.

Most intake manifolds have an EGR valve that regulates the amount of recirculated exhaust that enters the engine to reduce NOx emissions.

Exhaust manifolds can be made from cast iron or stainless steel.

The exhaust system also contains a catalytic converter, exhaust pipes, and muffler. The entire exhaust system is supported by rubber hangers that isolate the noise and vibration of the exhaust from the rest of the vehicle.



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REVIEW QUESTIONS

Why is it necessary to have intake charge velocities of about 50 feet per second?

Why can fuel-injected engines use larger (and longer) intake manifolds and still operate at low engine speed?

What is a tuned runner in an intake manifold?

How does a muffler quiet exhaust noise?



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CHAPTER QUIZ

1.Intake charge velocity has to be ________to prevent fuel droplet separation.

25 feet per second

50 feet per second

100 feet per second

300 feet per second



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CHAPTER QUIZ

2.The intake manifold of a port fuel-injected engine ________.

Uses a dual heat riser

Contains a leaner airfuel mixture than does the intake manifold of a TBI system

Contains only fuel (gasoline)

Contains only air



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CHAPTER QUIZ

3.Why are the EGR gases cooled before entering the engine on some engines?

Cool exhaust gas is more effective at controlling NOX emissions

To help prevent the exhaust from slowing down

To prevent damage to the intake valve

To prevent heating the airfuel mixture in the cylinder



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CHAPTER QUIZ

4.A heated air intake system is usually necessary for proper cold-engine driveability on ________.

Port fuel-injection systems

Throttle-body fuel-injection systems

Both a port-injected and throttle-body-injected engine

Any fuel-injected engine



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CHAPTER QUIZ

5.Air filters can remove particles and dirt as small as ________.

5 to 10 microns

10 to 25 microns

30 to 40 microns

40 to 50 microns



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CHAPTER QUIZ

6.Why do many port fuel-injected engines use long intake manifold runners?

To reduce exhaust emissions

To heat the incoming air

To increase high-RPM power

To increase low-RPM torque



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CHAPTER QUIZ

7.Exhaust passages are included in some intake manifolds. Technician A says that the exhaust passages are used for exhaust gas recirculation (EGR) systems. Technician B says that the exhaust heat is used to warm the intake charge on some engines equipped with a throttle-body-type fuel-injection system. Which technician is correct?

Technician A only

Technician B only

Both Technicians A and B

Neither Technician A nor B



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CHAPTER QUIZ

8.The upper portion of a two-part intake manifold is often called the ________.

Housing

Lower part

Plenum

Vacuum chamber



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CHAPTER QUIZ

9.Technician A says that a cracked exhaust manifold can affect engine operation. Technician B says that a leaking lower intake manifold gasket could cause a vacuum leak. Which technician is correct?

Technician A only

Technician B only





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CHAPTER QUIZ

10.Technician A says that some intake manifolds are plastic. Technician B says that some intake manifolds are constructed in two parts or sections: upper and lower. Which technician is correct?

Technician A only

Technician B only



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