AUTOMOTIVE TECHNOLOGY 3 (JA301)

CHAPTER 33CHAPTER FORCED INDUCTIONINDUCTIONFORCED SYSTEMSYSTEM

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FORCED INDUCTION SYSTEM A naturally aspirated (read that as carbureted) engine relies on the combustion cycle's and the scavenging effect of the exhaust as a means to draw air and atomized fuel through the intake manifold and into its cylinders. Forced induction (known as supercharging) on the other hand, uses a mechanical means to increase the pressure of the intake air charge, commonly referred to as boost.

Boosting the intake charge thrusts a larger quantity of air into the . More air, when mixed with more fuel, makes for a more powerful combustion burn. The stronger burn exerts more force on the , which in turn, pushes harder on the , obviously creating more power.

To burn a given amount of fuel, an exact amount of oxygen is required if the mixture is to be consumed without leaving excess fuel or oxygen behind. This chemically correct mixture is called stoichiometric (Stoichiometric or theoretical combustion is the ideal combustion process during which all fuel is burned completely). Most engines have to operate at or near this chemically correct mixture. AUTOMOTIVE TECHNOLOGY 3 (JA301)

Turbocharged system AUTOMOTIVE TECHNOLOGY 3 (JA301) AUTOMOTIVE TECHNOLOGY 3 (JA301) AUTOMOTIVE TECHNOLOGY 3 (JA301) AUTOMOTIVE TECHNOLOGY 3 (JA301) AUTOMOTIVE TECHNOLOGY 3 (JA301)

Advantages and disadvantages of a

Advantages 1). It is very light 2). It is not expensive 3). Increased peak power This power is useful when need to go fast, to pass someone, or if you live in an area with mountains, the increased power can be helpful in climbing the steep roads. 4). Decrease in exhaust emissions recycle the air used by the engine, which decreases the amount of fumes released into the atmosphere.

5). Turbochargers are generally quieter than Because its turbine is in the exhaust AUTOMOTIVE TECHNOLOGY 3 (JA301)

Disadvantages 1). Has turbo Lag

2).System that controls the fuel-to-oxygen ratio could malfunction Might not provide enough fuel to the engine

3).Works at a higher RPM. (Good for higher speed challenges. Bad for drag races)

4).Becomes hotter than a An becomes compulsory even for small low output turbochargers. 5). Difficult to install

6). Difficult to tune AUTOMOTIVE TECHNOLOGY 3 (JA301) Blow Off Valve Blow off valves are air pressure release valves that can be mounted on the intake piping of a turbocharged anywhere in between the turbo and the body. They are also known as dump valves, or vent valves.

It is actually a simple vacuum operated valve which releases air to the atmosphere or back into the intake. It is located right before the throttle body. There is two type of blow off valve system which is the blow off valve which releases the air to the atmosphere and there is the recirculation type, where the air is recirculated back into the intake system before the . The function of the blow off valve is to release the pressure in the whenever the throttle body is closed. The throttle body is closed whenever you released the accelerator pedal. That’s why you get the ‘pishh’ sound whenever you release the pedal during heavy acceleration. AUTOMOTIVE TECHNOLOGY 3 (JA301) AUTOMOTIVE TECHNOLOGY 3 (JA301)

The functions and important of a blow off valve A compressor is moved directly by the turbine via a shaft. So whenever the car is accelerated heavily or the car is in boost, pressure will be build up at the inlet manifold. Once you release the accelerator, for example to change gear, the throttle body will be fully closed. But the turbine is still turning due to the remaining exhaust gas and also the inertia of the turbo itself. This means that pressure in the inlet manifold will increase and need to find a way to get itself free. AUTOMOTIVE TECHNOLOGY 3 (JA301)

This is where the blow off valve work, the blow off valve will release the compressed air to the atmosphere or back to the air intake right before the compressor. Let say you don’t have the blow off valve, the compressed air will flow the other way around and against the air which is being compressed by the compressor and pass through the compressor and out to the filter. This phenomenon is called compressor surge.

The compressor surge is not good to the turbo as it can cause damage to the bearing and shorten the life of the turbo. Other than protecting the turbo, a blow off valve also increase the car response. It causes the compressor to spool up faster after each time the pedal is released and repressed again. AUTOMOTIVE TECHNOLOGY 3 (JA301)

How blow off valve works

A blow off valve is a simple vacuum operated valve. It gets the vacuum input from the inlet manifold after the throttle body.

So whenever the car is idling or boosting, a certain amount of pressure is available after the throttle body, but once you released the accelerator, the throttle body will fully close.

This will create a considerably low pressure or vacuum in the inlet manifold. When the blow off valve detects this vacuum, the blow off valve will open and release the pressure to atmosphere or bypass it into the air intake right before the compressor AUTOMOTIVE TECHNOLOGY 3 (JA301)

Blow off Valve Remain Closed When Throttle Body is Open AUTOMOTIVE TECHNOLOGY 3 (JA301)

Blow off Valve Open and Release the Air When The throttle Body is closed AUTOMOTIVE TECHNOLOGY 3 (JA301)

Supercharged system AUTOMOTIVE TECHNOLOGY 3 (JA301)

Roots Superchargers AUTOMOTIVE TECHNOLOGY 3 (JA301)

Twin-screw Superchargers AUTOMOTIVE TECHNOLOGY 3 (JA301)

Centrifugal Superchargers AUTOMOTIVE TECHNOLOGY 3 (JA301) AUTOMOTIVE TECHNOLOGY 3 (JA301) AUTOMOTIVE TECHNOLOGY 3 (JA301) Advantages/Disadvantages of a Supercharger

Advantages of a Supercharger 1). Increased power The greatest benefit to having a supercharger is the increased horsepower. Attach a supercharger to any car or truck, and the vehicle will operate as though it has a much larger, more powerful engine. This is because superchargers increase the engine's air-to-fuel mixture by forcing air into the engine; thereby increasing the push fuel receives entering the intake system.

2). No lag – Consistent power delivery Lag time is the amount of time it takes for a driver to push the gas pedal, and the car to respond. Superchargers are not affected by lag time. This increases engine response and performance, allowing the driver the get-off- the-line acceleration that they require in any racing or other performance- based situation. It is this lack of lag that makes a supercharger more attractive than a turbocharger, because it takes time for the exhaust in a turbocharger to achieve the appropriate velocity. AUTOMOTIVE TECHNOLOGY 3 (JA301)

3).Generally better throttle response

4). No Special Procedures or extra maintenance A supercharger requires no extra maintenance on the part of the driver. No out-of-the-ordinary shutdown procedures need be made because the supercharger does not depend on engine oil to run and requires no drainage. 5). Centrifugal Superchargers are more efficient at higher RPM

6). Roots & Twin Screw Superchargers are efficient at low RPM

7). Easier to tune

8). Easier to install than turbochargers A supercharger is easy to install as it can be attached to either the side or the top of an engine, though it does require substantial modification to the engine's AUTOMOTIVE TECHNOLOGY 3 (JA301)

Disadvantages of a Supercharger 1). Consumes a lot of power from the engine (therefore not very efficient)

2). Increases the strain on the engine

3). Increases the strain on the running gear 4). Expensive 5).Noise