.Voi posta in curand mai multe date despre turbo si altele.....
P.S. In curand in romana
Full Version: Engine Modifications
Ceva pentru inceput si incepatori .Voi posta in curand mai multe date despre turbo si altele.....
P.S. In curand in romana
.Voi posta in curand mai multe date despre turbo si altele.....
P.S. In curand in romana
Engine Modifications
In reference to producing a cars power, the most important single aspect to look at is flow. For starters, when tunning any vehicle for max (usefull and reliable) horsepower there really is only 3 things that are of importance:
a. increase stoichometric air/fuel flow
b. decrease/maintain safe heat levels
c. harness the power
Despite popular belief, when the accelerator is pushed it isn't giving the engine more gas. It is in actuality giving the car more air, by opening up the throttle body. The engines Management system is what gives the vehicle its gas. It is programmed so that when it sees more air entering the engine it will give it more gas. The best mixture that the engine could get is a perfect stoichometric mix. That means all the gas given to the engine is reacted with all the air that entered it. A vehicle that is considered to be running lean has more air then fuel. A vehicle that is considered to be running rich has more fuel than air. Since vehicles can't run a perfect stoich, it is better to run the vehicle lean. The lean conditions will increase an engines output however it will increase the chances of knocking and also called detonation. That's why car makers set up vehicles so that they will run slightly richer then desired. There are several ways to make a vehicle run leaner to increase horsepower. That will be discussed later in the engine management section. More flow equals more power
Engine Externals
Engine externals are located on the outside of the engine. They can be both attached to the engine or can be a supportive modification that is located far away from the engine (a fuel pump is a great example example). Externals contribute to about 95% of the modifications that the average person does. This is probably due to the ease of external modifications. The most common external modification is an air filter or exhaust upgrade. Upgrading these parts will give an approx 15% increase in engine output; of course it varies from vehicle to vehicle. The exhaust is one of the more noticeable modifications due to the increase in the exhaust tone. But a conical filter looks cooler under the hood. The sound of the intake will also be greatly increased. A very distinct whooshing noise is produced by a conical air filter.
Some examples of external modifications are listed below:
-Aftermarket Blow Off Valve / Bypass Valve (turbo vehicles only) This unit is specifically designed for turbocharged vehicles. When a turbo spools up it creates a pressure, this pressure can be both good and bad. When the throttle is decompressed, the backpressure will then want to go back towards the turbo, and spin it in the reverse direction. This will destroy a turbo. Thus a blow off valve(BOV) or bypass valve(BPV) is needed. Your choice of venting into atmosphere (BOV) or back into air intake tube(BPV). If venting into atmosphere car may have idle problems and can possibly stall out unless the intake flow is monitored after the BOV. This occurs because where the mass airflow sensor (MAS) is typically located. It makes the engine think that there is more air coming to it when in fact the air was just discharged into the atmosphere. It is in essence MIA air.
-Boost Controller This allows you to modify the amount of boost a turbo produces. It does this by tricking the turbo into thinking it is producing less boost then it really is thus it produces more until it reaches the boost point that was set. It in actuality tricks the wastegate actuator, the actuator is a device that prevents the turbo from overspooling, this could possible kill the turbo and or the engine; the boost controler bleeds off a set amount of vaccum pressure that is set. So for example if your car has a stock boost pressure of 11lbs and you put on a boost controller and set it to leak off 5lbs the turbo will spool up to 16, because the wastegate thinks 16lbs minus 5lbs, is entering into the engine
-Airfilter The filter is less restrictive allowing more air to flow, and the heat shield is a must when using an open conical filter because it helps prevent hot gases from the engine bay to enter into the engine which could cause detonation.
-Performance Battery Not a bad idea to get a new battery that keeps a more constant voltage allowing the electrical system to work more efficiently.
-Spark plugs ignites the air rushing into the engine. A spark plugs gap is very important When running boost at 17lbs and over a 0.028 gap is needed; 16lbs or less 0.032 will suffice. The smaller gap prevents the spark from being blow out. Larger gap will allow the engine to ignite the fuel mixture quicker.
-A turbo or supercharger will trust more air into the engine making it so the engine will produce more hp. An after market turbo will produce more boost then stock and will also push more CFM (cubic feet per minute) of air. The turbo is a very effiecient device; it will take the un used exhaust energy and turn it into boost pressure. When the exhaust leaves the manifold it is directed into something that is called a turbine. The turbine then gets accelerated to a very high speed, approx 100k RPM or 1667 revolutions a second (fast!). Some smaller ball-bearing turbos can get up to a blistering 200k RPM. The turbine then sends this kenitic energy along a shaft to the compressor, this is where the term "spooling" or "spooled up" comes from. The compressor sucks in the air from the outside and compresses it, this is called boost. Not only does the air mass get pressurized but it also gets heated up, and heated up air is not a good thing for an engine. Heated air will make the car knock like a mad man, thats why most turbo charged sytems come with an aftercooler, most commonly called and intercooler, named after the cooling sytem in massive truck turbo-chargers. A supercharger does the same thing a turbo does. It pushes more air into the engine. The only difference is, a superchargher is powered by the engines pulley system instead of the exhaust.
-Fuel Pump With elevated engine flow more fuel will be needed, and when the stock fuel levels are increased it will create stress on the smaller fuel pump. This will also on its own produce more pressure increasing the fuel flow.
-Upper Intercooler Piping facilitates airflow through the turbocharged engine. This peice is located between the turbo and the intercooler
-Lower Intercooler Piping facilitates airflow through the turbocharged engine, by increasing airflow effiency. This peice is located between the intercooler and the throttle body.
-Intake Pipe The stock tube is highly restrictive and very turbulent. By replacing the stock piece it will allow a more efficient flow.
-A fuel pressure regulator will allow you to adjust your fuel pressure more accurately to compensate for higher flow.
-Exhaust manifold This is used to rid the exhaust from the engine heads, higher flowing is better to maximize exhaust efficiency.
-Larger injectors allows more fuel to flow more efficiently. Allows better atomization of the gas to give a more combustible gas charged air/fuel mixture.
-An Intercooler is a must have with a turbo setup, and sometimes a supercharger setup. With elavated boost levels and a higher flow it is harder to cool down the air mass; a nice cool charge will not only make your car run faster, about 1% power increase for every 11 degree drop, but it will keep your car safe from detonation. Detonation is caused when the air/fuel mass entering the engine pre-ignites, this on its own isnt bad for your car, the part that makes this bad is when the extra explosion heats up the cylinders an extra amount, possibly causing them to get fried. The race core, and most larger cores, makes it so there is less of a pressure drop across the intercooler; less pressure drop means more ponies.
-An upgraded cooling fan will increase the cooling power of the engine, so that safe running heat levels can be maintained.
-Ignition wires Increases the charge density to the spark plugs to increase the spark, thus igniting the air/fuel more efficiently.
-A MAF Translator is used to connect up a 3 inch GM mass air flow sensor (MAF). This device also allows me to compensate for larger injectors. This device modifies the airflow signal that the GM MAF sends to allow the eclipses ecu to interpret it. This was bought so that the car could use a blow off valve opposed to a by pass valve.
-3inch GM MAF This works directly with the MAF Translator; this could not be used with out it. Read about MAF Translator for more info.
-Valve Cover This covers the camshafts, and keeps them protected from the elements.
-Fuse Box Holds all the larger electrical component fuses.
-Radiator Overflow Bottle When the radiator gets very hot and all the excess fluid expands it needs to go somewhere. The extra fluid drains into this bottle. In the past older vehicle never had overflow bottles and the radiator coolant would just leak onto the highway. It wasn't healthy for the environment, other animals, and it makes the roads unnecessarily slick.
-Timing Belt The timing belt transfers energy from the crank to the camshafts.
-Radiator The radiator uses an air to water to air cooling method. The radiator takes the hot boiling water/antifreeze mixture and cools it off before going back to the engine then it repeats the cycle.
-Cruise Control Actuator This item has nothing to do with engine performance. All it does is hold the throttle at a given postion depending upon the speed you set.
Engine Internals
Engine internals consists of what is inside the engine block and heads. The engine block is what produces the power. The head allows the block to produce the power. Most performance modifications done to cars aren't internal. Internal modifications are not only the hardest but most often most time consuming. Modifying engine internals in a lot of vehicles is also very technical. The block can have several parts upgraded in it. A stronger and lighter crank can be added to a vehicle. This will decrease the centrifugal energy, and will increase the integrity of the motors ability to hold the power being produce. Replacing the stock connecting rods with lighter and stronger ones will do much the same as with the crank. Pistons are also very important, stronger and lighter pistons are important; something that is just as important is engine compression. For the most part the compression of a vehicles engine is made by the pistons. A higher compression is usually desired. But in some cases a lower compression is desired. When a vehicle is boosted either with a supercharger or a turbo, lower compression is better then higher. Higher compression increases the chances of the engine knocking, which isn't good, and with a turbo or a supercharger the chances increase dramatically. This is due to the air being thrust into the engine increasing the engines internal pressure thus increasing how much the air charge is compressed. The area between the block and the heads uses a gasket to connect them together. This gasket is very important; it allows heads to be tightly sealed against the block. A stronger gasket is strongly recommended when high boost levels are being applied to the engine. The gasket can also be used to decrease the compression of an engine. A thicker gasket will decrease how much the engine compresses the air. This however is not the best way to decrease compression. The heads contains the valves and valve springs. Once again lighter and stronger is always better. In most new cars the head also contains the camshafts. In older vehicle a single cam shaft was located in the block above the crank. Push rods where used to transfer the cam's push onto a roller rocker then to the valve. Newer cars have something called over head cams, either one or two camshafts. If a vehicle has dual camshafts it is called a DOHC, a single cam is called SOHC. DOHC is better then a SOHC. In a DOHC engine one cam is used to control the exhaust valves and the air valves. Timing of the camshafts with the engines rotation is very important. If they are off sync with each other it is possible to damage a engine by bending valves. The engine will also not run if completely out of sync. Engines are usually setup by the manufacturer so that it runs the smoothest. Slightly retarded or advanced timing will make a car idle horrible, but can also shift and increase an engines power range. After market cam wheels are great for adjusting cam timming.
Engine Management
Engine management is used to control the fuel and air mixture. Engine management is composed of many sensors and the Engine Control Module; this is also called an ECU or ECM. The easiest way and most cost effective way to upgrade the management system is to use a piggy back method. The piggy back method enables the stock, and well designed ECU to be used while enabling a user to tune his or her vehicle. These systems are used to adjust a vehicles mass air flow signal to richen or lean a vehicle. The best example of this device is the Apexi S-AFC . The best way to tune a vehicle is with a stand alone unit. The stand alone unit replaces the stock ECU entirely. This system is very reliable and tunable. Almost every aspect of a vehicle can be tuned with this, anything from air fuel mixture to spark timing. A great example of one of these units is the AEM EMS stand alone unit. However the stand alone unit is not recommended for an amateur tuner. It is very easy to get lost in the programming of one of these units. The piggy back units are relatively easy to setup and do not cost as much as a stand alone. A stand alone unit also requires the use of a laptop or a computer to tune it.
Engine Protection and Monitoring
Engine protection and monitoring is very important. Without this it is hard to tell the limits of an engine. Most of the tell tale signs of a failing engine can't be seen by the naked eye. Thus aftermarket gauges are needed to be used by the driver so that warning signs can be seen before things start to break. The gauges are used to monitor things like:
• Engine temp
• Exhaust temp (indicates a knocking situation when very high)
• Transmission Temp
• Oil pressure
• Air/fuel ratio
• RPM
• Knock signal
1.Knocking (also called pinking or pinging) technically detonation in internal combustion engines occurs when fuel in the cylinder is ignited by the firing of the spark plug and smooth burning proceeds but some of the unburned mixture in the combustion chamber explodes before the flame front can reach it, combusting suddenly before the optimum moment of the four-stroke cycle. The resulting shockwave collides with the rising piston, creating a characteristic metallic pinging sound.
2.Camshaft The camshaft is an apparatus used in piston engines to operate poppet valves. It consists of a cylindrical rod running the length of the cylinder bank with a number of oblong lobes or cams protruding from it, one for each valve. The cams force the valves open by pressing on the valve, or on some intermediate mechanism, as they rotate.
The relationship between the rotation of the camshaft and the rotation of the crankshaft is of critical importance. Since the valves control the flow of fuel intake and exhaust, they must be opened and closed at the appropriate time during the stroke of the piston. For this reason, the camshaft is connected to the crankshaft either directly, via a gear mechanism, or indirectly via a belt or chain called a timing belt or timing chain. In some designs the camshaft also drives the distributor and the oil and fuel pumps. Also on early fuel injection systems, cams on the camshaft would operate the fuel injectors.
In a two-stroke engine that uses a camshaft, each valve is opened once for each rotation of the crankshaft; in these engines, the camshaft rotates at the same rate as the crankshaft. In a four-stroke engine, the valves are opened only half as often; thus, two full rotations of the crankshaft occur for each rotation of the camshaft.
Depending on the location of the camshaft, the cams operate the valves either directly or through a linkage of pushrods and rockers. Direct operation involves a simpler mechanism and leads to fewer failures, but requires the camshaft to be positioned at the top of the cylinders. In the past when engines were not as reliable as today this was seen as too much bother, but in modern gasoline engines the overhead cam system, where the camshaft is on top of the cylinder head, is quite common. Some engines use one camshaft each for the intake and exhaust valves; such an arrangement is known as a double or dual overhead cam (DOHC), thus, a V engine may have 4 camshafts.
In reference to producing a cars power, the most important single aspect to look at is flow. For starters, when tunning any vehicle for max (usefull and reliable) horsepower there really is only 3 things that are of importance:
a. increase stoichometric air/fuel flow
b. decrease/maintain safe heat levels
c. harness the power
Despite popular belief, when the accelerator is pushed it isn't giving the engine more gas. It is in actuality giving the car more air, by opening up the throttle body. The engines Management system is what gives the vehicle its gas. It is programmed so that when it sees more air entering the engine it will give it more gas. The best mixture that the engine could get is a perfect stoichometric mix. That means all the gas given to the engine is reacted with all the air that entered it. A vehicle that is considered to be running lean has more air then fuel. A vehicle that is considered to be running rich has more fuel than air. Since vehicles can't run a perfect stoich, it is better to run the vehicle lean. The lean conditions will increase an engines output however it will increase the chances of knocking and also called detonation. That's why car makers set up vehicles so that they will run slightly richer then desired. There are several ways to make a vehicle run leaner to increase horsepower. That will be discussed later in the engine management section. More flow equals more power
Engine Externals
Engine externals are located on the outside of the engine. They can be both attached to the engine or can be a supportive modification that is located far away from the engine (a fuel pump is a great example example). Externals contribute to about 95% of the modifications that the average person does. This is probably due to the ease of external modifications. The most common external modification is an air filter or exhaust upgrade. Upgrading these parts will give an approx 15% increase in engine output; of course it varies from vehicle to vehicle. The exhaust is one of the more noticeable modifications due to the increase in the exhaust tone. But a conical filter looks cooler under the hood. The sound of the intake will also be greatly increased. A very distinct whooshing noise is produced by a conical air filter.
Some examples of external modifications are listed below:
-Aftermarket Blow Off Valve / Bypass Valve (turbo vehicles only) This unit is specifically designed for turbocharged vehicles. When a turbo spools up it creates a pressure, this pressure can be both good and bad. When the throttle is decompressed, the backpressure will then want to go back towards the turbo, and spin it in the reverse direction. This will destroy a turbo. Thus a blow off valve(BOV) or bypass valve(BPV) is needed. Your choice of venting into atmosphere (BOV) or back into air intake tube(BPV). If venting into atmosphere car may have idle problems and can possibly stall out unless the intake flow is monitored after the BOV. This occurs because where the mass airflow sensor (MAS) is typically located. It makes the engine think that there is more air coming to it when in fact the air was just discharged into the atmosphere. It is in essence MIA air.
-Boost Controller This allows you to modify the amount of boost a turbo produces. It does this by tricking the turbo into thinking it is producing less boost then it really is thus it produces more until it reaches the boost point that was set. It in actuality tricks the wastegate actuator, the actuator is a device that prevents the turbo from overspooling, this could possible kill the turbo and or the engine; the boost controler bleeds off a set amount of vaccum pressure that is set. So for example if your car has a stock boost pressure of 11lbs and you put on a boost controller and set it to leak off 5lbs the turbo will spool up to 16, because the wastegate thinks 16lbs minus 5lbs, is entering into the engine
-Airfilter The filter is less restrictive allowing more air to flow, and the heat shield is a must when using an open conical filter because it helps prevent hot gases from the engine bay to enter into the engine which could cause detonation.
-Performance Battery Not a bad idea to get a new battery that keeps a more constant voltage allowing the electrical system to work more efficiently.
-Spark plugs ignites the air rushing into the engine. A spark plugs gap is very important When running boost at 17lbs and over a 0.028 gap is needed; 16lbs or less 0.032 will suffice. The smaller gap prevents the spark from being blow out. Larger gap will allow the engine to ignite the fuel mixture quicker.
-A turbo or supercharger will trust more air into the engine making it so the engine will produce more hp. An after market turbo will produce more boost then stock and will also push more CFM (cubic feet per minute) of air. The turbo is a very effiecient device; it will take the un used exhaust energy and turn it into boost pressure. When the exhaust leaves the manifold it is directed into something that is called a turbine. The turbine then gets accelerated to a very high speed, approx 100k RPM or 1667 revolutions a second (fast!). Some smaller ball-bearing turbos can get up to a blistering 200k RPM. The turbine then sends this kenitic energy along a shaft to the compressor, this is where the term "spooling" or "spooled up" comes from. The compressor sucks in the air from the outside and compresses it, this is called boost. Not only does the air mass get pressurized but it also gets heated up, and heated up air is not a good thing for an engine. Heated air will make the car knock like a mad man, thats why most turbo charged sytems come with an aftercooler, most commonly called and intercooler, named after the cooling sytem in massive truck turbo-chargers. A supercharger does the same thing a turbo does. It pushes more air into the engine. The only difference is, a superchargher is powered by the engines pulley system instead of the exhaust.
-Fuel Pump With elevated engine flow more fuel will be needed, and when the stock fuel levels are increased it will create stress on the smaller fuel pump. This will also on its own produce more pressure increasing the fuel flow.
-Upper Intercooler Piping facilitates airflow through the turbocharged engine. This peice is located between the turbo and the intercooler
-Lower Intercooler Piping facilitates airflow through the turbocharged engine, by increasing airflow effiency. This peice is located between the intercooler and the throttle body.
-Intake Pipe The stock tube is highly restrictive and very turbulent. By replacing the stock piece it will allow a more efficient flow.
-A fuel pressure regulator will allow you to adjust your fuel pressure more accurately to compensate for higher flow.
-Exhaust manifold This is used to rid the exhaust from the engine heads, higher flowing is better to maximize exhaust efficiency.
-Larger injectors allows more fuel to flow more efficiently. Allows better atomization of the gas to give a more combustible gas charged air/fuel mixture.
-An Intercooler is a must have with a turbo setup, and sometimes a supercharger setup. With elavated boost levels and a higher flow it is harder to cool down the air mass; a nice cool charge will not only make your car run faster, about 1% power increase for every 11 degree drop, but it will keep your car safe from detonation. Detonation is caused when the air/fuel mass entering the engine pre-ignites, this on its own isnt bad for your car, the part that makes this bad is when the extra explosion heats up the cylinders an extra amount, possibly causing them to get fried. The race core, and most larger cores, makes it so there is less of a pressure drop across the intercooler; less pressure drop means more ponies.
-An upgraded cooling fan will increase the cooling power of the engine, so that safe running heat levels can be maintained.
-Ignition wires Increases the charge density to the spark plugs to increase the spark, thus igniting the air/fuel more efficiently.
-A MAF Translator is used to connect up a 3 inch GM mass air flow sensor (MAF). This device also allows me to compensate for larger injectors. This device modifies the airflow signal that the GM MAF sends to allow the eclipses ecu to interpret it. This was bought so that the car could use a blow off valve opposed to a by pass valve.
-3inch GM MAF This works directly with the MAF Translator; this could not be used with out it. Read about MAF Translator for more info.
-Valve Cover This covers the camshafts, and keeps them protected from the elements.
-Fuse Box Holds all the larger electrical component fuses.
-Radiator Overflow Bottle When the radiator gets very hot and all the excess fluid expands it needs to go somewhere. The extra fluid drains into this bottle. In the past older vehicle never had overflow bottles and the radiator coolant would just leak onto the highway. It wasn't healthy for the environment, other animals, and it makes the roads unnecessarily slick.
-Timing Belt The timing belt transfers energy from the crank to the camshafts.
-Radiator The radiator uses an air to water to air cooling method. The radiator takes the hot boiling water/antifreeze mixture and cools it off before going back to the engine then it repeats the cycle.
-Cruise Control Actuator This item has nothing to do with engine performance. All it does is hold the throttle at a given postion depending upon the speed you set.
Engine Internals
Engine internals consists of what is inside the engine block and heads. The engine block is what produces the power. The head allows the block to produce the power. Most performance modifications done to cars aren't internal. Internal modifications are not only the hardest but most often most time consuming. Modifying engine internals in a lot of vehicles is also very technical. The block can have several parts upgraded in it. A stronger and lighter crank can be added to a vehicle. This will decrease the centrifugal energy, and will increase the integrity of the motors ability to hold the power being produce. Replacing the stock connecting rods with lighter and stronger ones will do much the same as with the crank. Pistons are also very important, stronger and lighter pistons are important; something that is just as important is engine compression. For the most part the compression of a vehicles engine is made by the pistons. A higher compression is usually desired. But in some cases a lower compression is desired. When a vehicle is boosted either with a supercharger or a turbo, lower compression is better then higher. Higher compression increases the chances of the engine knocking, which isn't good, and with a turbo or a supercharger the chances increase dramatically. This is due to the air being thrust into the engine increasing the engines internal pressure thus increasing how much the air charge is compressed. The area between the block and the heads uses a gasket to connect them together. This gasket is very important; it allows heads to be tightly sealed against the block. A stronger gasket is strongly recommended when high boost levels are being applied to the engine. The gasket can also be used to decrease the compression of an engine. A thicker gasket will decrease how much the engine compresses the air. This however is not the best way to decrease compression. The heads contains the valves and valve springs. Once again lighter and stronger is always better. In most new cars the head also contains the camshafts. In older vehicle a single cam shaft was located in the block above the crank. Push rods where used to transfer the cam's push onto a roller rocker then to the valve. Newer cars have something called over head cams, either one or two camshafts. If a vehicle has dual camshafts it is called a DOHC, a single cam is called SOHC. DOHC is better then a SOHC. In a DOHC engine one cam is used to control the exhaust valves and the air valves. Timing of the camshafts with the engines rotation is very important. If they are off sync with each other it is possible to damage a engine by bending valves. The engine will also not run if completely out of sync. Engines are usually setup by the manufacturer so that it runs the smoothest. Slightly retarded or advanced timing will make a car idle horrible, but can also shift and increase an engines power range. After market cam wheels are great for adjusting cam timming.
Engine Management
Engine management is used to control the fuel and air mixture. Engine management is composed of many sensors and the Engine Control Module; this is also called an ECU or ECM. The easiest way and most cost effective way to upgrade the management system is to use a piggy back method. The piggy back method enables the stock, and well designed ECU to be used while enabling a user to tune his or her vehicle. These systems are used to adjust a vehicles mass air flow signal to richen or lean a vehicle. The best example of this device is the Apexi S-AFC . The best way to tune a vehicle is with a stand alone unit. The stand alone unit replaces the stock ECU entirely. This system is very reliable and tunable. Almost every aspect of a vehicle can be tuned with this, anything from air fuel mixture to spark timing. A great example of one of these units is the AEM EMS stand alone unit. However the stand alone unit is not recommended for an amateur tuner. It is very easy to get lost in the programming of one of these units. The piggy back units are relatively easy to setup and do not cost as much as a stand alone. A stand alone unit also requires the use of a laptop or a computer to tune it.
Engine Protection and Monitoring
Engine protection and monitoring is very important. Without this it is hard to tell the limits of an engine. Most of the tell tale signs of a failing engine can't be seen by the naked eye. Thus aftermarket gauges are needed to be used by the driver so that warning signs can be seen before things start to break. The gauges are used to monitor things like:
• Engine temp
• Exhaust temp (indicates a knocking situation when very high)
• Transmission Temp
• Oil pressure
• Air/fuel ratio
• RPM
• Knock signal
1.Knocking (also called pinking or pinging) technically detonation in internal combustion engines occurs when fuel in the cylinder is ignited by the firing of the spark plug and smooth burning proceeds but some of the unburned mixture in the combustion chamber explodes before the flame front can reach it, combusting suddenly before the optimum moment of the four-stroke cycle. The resulting shockwave collides with the rising piston, creating a characteristic metallic pinging sound.
2.Camshaft The camshaft is an apparatus used in piston engines to operate poppet valves. It consists of a cylindrical rod running the length of the cylinder bank with a number of oblong lobes or cams protruding from it, one for each valve. The cams force the valves open by pressing on the valve, or on some intermediate mechanism, as they rotate.
The relationship between the rotation of the camshaft and the rotation of the crankshaft is of critical importance. Since the valves control the flow of fuel intake and exhaust, they must be opened and closed at the appropriate time during the stroke of the piston. For this reason, the camshaft is connected to the crankshaft either directly, via a gear mechanism, or indirectly via a belt or chain called a timing belt or timing chain. In some designs the camshaft also drives the distributor and the oil and fuel pumps. Also on early fuel injection systems, cams on the camshaft would operate the fuel injectors.
In a two-stroke engine that uses a camshaft, each valve is opened once for each rotation of the crankshaft; in these engines, the camshaft rotates at the same rate as the crankshaft. In a four-stroke engine, the valves are opened only half as often; thus, two full rotations of the crankshaft occur for each rotation of the camshaft.
Depending on the location of the camshaft, the cams operate the valves either directly or through a linkage of pushrods and rockers. Direct operation involves a simpler mechanism and leads to fewer failures, but requires the camshaft to be positioned at the top of the cylinders. In the past when engines were not as reliable as today this was seen as too much bother, but in modern gasoline engines the overhead cam system, where the camshaft is on top of the cylinder head, is quite common. Some engines use one camshaft each for the intake and exhaust valves; such an arrangement is known as a double or dual overhead cam (DOHC), thus, a V engine may have 4 camshafts.
Sa zicem ca unii inteleg ce se scrie acolo mai sus, dar restul??
Bine ar fii si ceva traducere. Nu motamo, ci ideile principale :wink:
Bine ar fii si ceva traducere. Nu motamo, ci ideile principale :wink:
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