What's a throttle body? 
I'll get my coat.
In a fuel injection engine, the throttle body is the part of the air intake system that controls the amount of air flowing into the engine, in response to driver input. While the accelerator is often called a "gas pedal", it would be more accurate to describe it as an "air pedal". In a fuel injection engine, the throttle body is the part of the air intake system that controls the amount of air flowing into the engine, in response to driver input. While the accelerator is often called a "gas pedal", it would be more accurate to describe it as an "air pedal".
The throttle body is usually located between the air filter box and the intake manifold, and usually attached to, or near, the mass airflow sensor.
The largest piece inside the throttle body is the throttle plate, which is a butterfly valve that regulates the airflow.
On many cars, the accelerator pedal motion is communicated through the throttle cable, which activates the throttle linkages, which moves the throttle plate. In cars with electronic throttle control (also known as "drive-by-wire"), an electric motor controls the throttle linkages and the accelerator cable connects not to the throttle body but to a sensor. The ECU determines the throttle opening.
When the driver presses on the accelerator pedal, the throttle plate opens up, allowing more air into the intake manifold. Either a throttle position sensor or an airflow sensor measures this change and communicates with the ECU. The ECU then increases the amount of fuel being sent to the fuel injectors in order to maintain the desired air-fuel ratio.
Throttle bodies may also contain valves and adjustments to control the minimum airflow during idle. Even in those units that are not "drive-by-wire" there may be a small electric motor that the ECU uses to modify the throttle opening.
Many cars have a single throttle body, however more than one may be used, chained together by linkages, to improve throttle response. At the extreme end, cars such as the BMW M1 have a separate throttle body for each cylinder.
A throttle body is somewhat analogous to the carburetor in a non-injected engine. Carburetors combine the functionality of the throttle body and the fuel injectors into one, that is, to modulate the amount of air flow, and to combine air and gas together. Cars with throttle body injection (called TBI by General Motors and CFI by Ford) locate the fuel injectors in the throttle body, thereby allowing an older engine to be converted from carburetor to fuel injection without altering significantly the engine design.
An intake is an air intake for an engine. Because the modern internal combustion engine is in essence a powerful air pump, like the exhaust system on an engine, the intake must be carefully engineered and tuned to provide the greatest efficiency and power. An ideal intake system should increase the velocity of the air until it travels in to the combustion chamber, while minimizing turbulence and restriction of flow. This is usually accomplished by flow testing on a flow bench in the port design stage. Cars with turbo chargers or superchargers which provide a pressurized intake system, usually have extensive tweaking of the intake system to improve performance dramatically.
A modern air intake system should have three main parts, an air filter, mass flow sensor, and throttle body. Many cars today now include a silencer to minimize the noise entering the cabin. Silencers impede air flow and create turbulence which reduce total power, so many performance enthusiasts often remove them.
Production cars have specific length air intakes to cause the air to vibrate and buffett at a specific frequency to assist air flow in to the combustion chamber. Aftermarket companies for cars have introduced larger throttle bodies and air filters to decrease restriction of flow at the cost of changing the harmonics of the air intake for a small net increase in power or torque.
BMW is unusual in that its M line of performance cars have one throttle body per cylinder, as opposed to one throttle body for four, six or even eight cylinders for regular production cars. This is done to increase flow characteristics and improve throttle response. Nissan also use this system in their high performance models.
Porsche in the 1980s designed an intake system for their cars that changed the length of the intake system by alternating between a longer and shorter set of tubing using a butterfly valve, creating a small amount of positive pressure which increased overall performance of the engine.
In automotive engineering, an intake manifold or inlet manifold is a part of an engine that supplies the fuel/air mixture to the cylinders. An exhaust manifold or header collects the exhaust gases from multiple cylinders into one pipe.
The word "manifold" literally means "hand shaped", which arises from the "fingers" leading to or away from each cylinder.
Due to the suction effect of the downward movement of the pistons in a reciprocating piston engine, a partial vacuum (lower than atmospheric pressure) exists in the intake manifold. If the engine has a throttle valve (i.e. in spark ignition rather than diesel engines) this manifold vacuum can be substantial, and can be used as a source of automobile ancillary power to drive auxiliary systems: (ignition advance, power assisted brakes, cruise control, windscreen wipers, power windows, ventilation system valves, etc). This vacuum can also be used to 'suck' any piston blow-by gases from the engine's crankcase. This is known as a closed crankcase ventilation or positive crankcase ventilation (PCV) system. This way the gases are burned with the fuel/air mixture.
The intake manifold is usually made of aluminium and located between the carburetor and the cylinder head. On multi point injected engines, the intake manifold holds the fuel injectors.
Exhaust manifolds are generally and traditionally simple cast iron units which collect engine exhaust and deliver it to the exhaust pipe. However, when greater performance is required, this restrictive tube is often replaced with individual headers which are tuned for low restriction and improved performance. There are two types of headers. Collector style headers use pipes that merge into a collector, and can be utilized with mufflers. Collector headers can be used for the street or for a race car. Zoomie headers have no collectors, and are used exclusively on race cars. Headers have been widely available from aftermarket sources for decades, and some manufacturers have begun using them as original equipment. The Honda J30A2 engine does away with exhaust manifolds altogether, using an integral engine block passage to route gases directly to the catalytic converter.
Electronic throttle control (ETC) is an automobile technology which severs the mechanical link between the accelerator pedal and the throttle. Most automobiles already use a throttle position sensor (TPS) to provide input to traction control, antilock brakes, fuel injection, and other systems, but use a bowden cable to directly connect the pedal with the throttle. An ETC-equipped vehicle has no such cable. Instead, the electronic control unit (ECU) determines the required throttle position by calculations from data measured by other sensors such as an accelerator pedal position sensor, engine speed sensor, vehicle speed sensor etc. The electric motor within the ETC is then driven to the required position via a closed-loop control algorithm within the ECU.
The benefits of ETC are largely unnoticed by most drivers because the aim is to make the vehicle power-train characteristics seamlessly consistent irrespective of prevailing conditions, such as engine temperature, altitude, accessory loads etc. The ETC is also working 'behind the scenes' to dramatically improve the ease with which the driver can execute gear changes and deal with the dramatic torque changes associated with rapid accelerations and decelerations.
Contrary to popular belief, except in concert with other technologies such as gasoline direct injection, ETC provides only a very limited benefit in areas such as air-fuel ratio control, exhaust emissions and fuel consumption reduction. ETC however makes it much easier to integrate features to the vehicle such as cruise control, traction control, stability control and others that require torque management, since the throttle can be moved irrespective of the position of the driver's accelerator pedal. A criticism of the very early ETC implementations was that they were "overruling" driver decisions. Nowadays, the vast majority of drivers have no idea how much intervention is happening.
Much of the engineering involved with drive-by-wire technologies including ETC deals with failure and fault management. Most ETC systems have sensor and controller redundancy, even as complex as independent microprocessors with independently written software within a control module whose calculations are compared to check for possible errors and faults.
Anti-lock braking (ABS) is a similar safety critical technology, whilst not completely 'by-wire', it has the ability to electronically intervene contrary to the driver's demand. Such technology has recently been extended to other vehicle systems to include features like brake assist and electronic steering control, but these systems are much less common, also requiring careful design to ensure appropriate back-up and fail-safe modes.
As of 2005, the Toyota Prius is the most prominent example of drive-by-wire technology, featuring electronic throttle, brake and transmission control. This is largely by necessity of the Hybrid Synergy Drive system, which assigns complete engine control and regenerative/friction braking decisions to a hybrid control computer. Further extending the drive-by-wire concept, in Europe and Japan automatic parking assist is also available — the car can control the steering to guide itself backwards into a parking space.
Some fanciful theories and applications abound as to what the ultimate implications of drive-by-wire technology might be. It has been suggested that drive-by-wire might allow a car to become completely separate from its controls, meaning that a car of the future might theoretically be controlled by any number of different control systems: push buttons, joysticks, steering wheels, or even voice commands — whatever device that designers could come up with. (This would have many advantages, such as increased flexibility for handicapped or disabled drivers.) Coupled with fuel cell applications, futuristic designs for such a car have been proposed, including a car whose entire functional driving components are concentrated in its chassis — the actual 'shell' of the car being a module that can be swapped out and replaced with different models as the driver dictates. Competitors in the DARPA Grand Challenge, an automated driving competition, relied on 100% drive-by-wire systems, in some cases including a steer-by-wire system provided by the manufacturer...............................
I could go on........................
Edited by P11 COV, 31 August 2006 - 10:31 PM.
