Inlet Camshaft Impreza V1-4

STI  Subaru Tecnica International Inc. (STI) is a subsidiary of Fuji Heavy Industries Ltd. (FHI), which was established to undertake the motorsport activities of SUBARU. STI's core business is supplying motorsport base vehicles and competition parts and planning and developing SUBARU Limited Edition Models by applying special tuning techniques as well as planning and selling accessories and tuning parts to add variety to car life for auto enthusiasts worldwide. Through these operations, STI aims to provide its many SUBARU fans with special satisfaction. In 1972, FHI participated in the Southern Cross Rally in Australia with the first Japanese FF car - the Leone, before bringing out the Leone 4WD (the first AWD car in the WRC) in the Safari Rally in 1980. Following this, in order to respond to a new generation of motorsport with AWD turbo cars, which was expected to take off, STI was established in April 1988. Its founder and then president, the late Mr. Ryuichiro Kuze, was a board director of FHI and a co-driver in the Leone when it debuted in the Southern Cross Rally in 1972. As soon as he founded STI, he and his company planned and operated an event to challenge the world speed record in Arizona in the USA with the first Legacy which would herald in the future for SUBARU. In the event, the Legacy set a new world speed record for 100,000 consecutive kilometres of driving, a record which STI held for 16 years. This is how STI with its mission ‘to make SUBARU world number one', embarked on its journey as a brand which already was enjoying the world's number 1 title. After refining its AWD technology through a demanding Safari Rally, SUBARU began full-participation in the WRC with the Legacy, starting from Safari in 1990. STI's founder, Kuze teamed up with an up and coming British team to form the SUBARU World Rally Team the same year. Starting from the Acropolis Rally in Greece, the team competed under a new Japan-UK organisational structure, with the Japanese side in charge of engines and the British, the chassis. Meanwhile, STI's WRC activities for SUBARU led to the development of a car that could win in the WRC, and in 1992 this was finally embodied as a package - the Impreza. In the WRC, SUBARU clinched their first victory with the Legacy in New Zealand in 1993 before the succeeding Impreza came in 2nd outright in its debut event in Finland the same year. SUBARU made rapid progress after that. They finished the 1994 WRC in 2nd with 3 wins in the season. In 1995 and 96, they won rally after rally with an unstoppable force, and walked off with the WRC manufacturers' title for both years. As the World Rally Car regulation was newly enforced in 1997, the Impreza WRC, which had been developed in compliance with the new vehicle regulation, remarkably won 8 out of the season's 14 rallies that year to become the first Japanese car to be crowned as the WRC Manufacturers' Champion for three consecutive years. Released in November 1992, the Impreza was first used in the WRC in the mid stage of 1993. Although it already had 240PS as standard, it was required to introduce an evolution model to fight against formidable European rivals in the WRC. As a result, the WRX-STI was released in January 1994. Based on the WRX turbo model, WRX STI was equipped with forged pistons, a special ECU and larger muffler. With increased power to 250PS, this model was only built to order and the engine was fine-tuned by STI. Following a minor change in the Impreza in October 1994, an STI version was also released to much accolade. This STI Version featured the Drivers Control Centre Differential (DCCD) as well as a power increase to 275PS thanks to the reinforced cylinder heads and enhanced turbo boost pressure. Its success allowed the STI Version, which was then a limited edition model, to go into mass-production with its catalogue model from Version II in 1995 onward. Since then, the STI Version of the first Impreza - the GC8 type evolved into Version III featuring 280PS in 1996, and then up to Version VI released in 1999. While the Impreza STI Version, initially released as an evolution model for the WRC, continued to develop as a production car, STI planned a series of special specification models with even higher performance. The Impreza 22B STI Version, which was developed to celebrate SUBARU's three consecutive WRC Manufacturers' titles between 1995 and 97, was particularly revolutionary. Fitted with the same wide blister fender used in the Impreza World Rally Car, this model enjoyed a rush of orders upon its release in March 1998, and sold out immediately. As expected, this model enhanced the STI brand, and so STI took a big step forward towards its ideal - to become the figurehead for SUBARU. This direction of premium sport sedans in a limited number continued through the Impreza S201, which was released at the later stage of the GC8 type, and after the full model change of the Impreza in 2000, the S202, S203 and S204, which were all based on the GDB type Impreza. Following the full model change of the Impreza in 2000, the World Rally Car version's base was changed to the GDB type in 2001. Around that time, strong European manufacturers entered the World Rally Car field one after the other and the Impreza WRC improved its performance through competitions against these rivals. Driving the GDB type Impreza, Richard Burns became SUBARU's second WRC drivers' champion in 2001 - the GDB type Impreza's debut year, following Colin McRae in 1995. Then Petter Solberg won the championship behind the wheel of an Impreza, and proving the SUBARU is fast with anyone. SUBARU has won 47 WRC rallies - the most of any Japanese manufacturer; 46 of them in an Impreza, and so, this car now is known familiarly as a true world-class sport sedan among rally fans around the world. Furthermore, in another world championship, the PWRC where Group N cars of near-showroom specification compete, drivers in the Impreza won the title for 4 consecutive years from 2003, including a long-cherished world title for Japanese top rally driver Toshi Arai in 2005 - an achievement he then repeated in 2007. In rallying with Group N vehicles, which are closely based on their production model counterparts, victory cannot be guaranteed without good features in the original base model. While the Impreza WRX STI has established its position as a production model of FHI, STI's development department in close ties with FHI has introduced detailed specification changes at every annual revamp in order for the vehicle to be able to continually display high performance in rally competitions at a customer level. Consequently, the Impreza continued to make brilliant progress especially in the second half of 2000 in national and regional rally championships all around the world. In this way, the ever-evolving Impreza WRX STI consolidates and incorporates feedback and requests from the worldwide motorsport field. At the end of 2008, FHI announced its withdrawal from its WRC programme at a works team level. Following this decision, STI started to consider trying motorsport categories in which the company can capitalise on technologies and resources developed through the WRC to date. One idea was to continue offering their expertise to a GT300 vehicle in the Japanese SUPER GT series. Although racing conditions are different, challenges such as instantaneously delivering strong performance and maintaining durability and capability under harsh conditions are the same as in the WRC. Since the start of development of a new GT300 race car based on the Legacy in 2009, STI has utilised a string of ideas to develop the performance of the horizontally opposed turbo engine for a GT300 vehicle in conjunction with FHI and R&D SPORT which is in charge of team operations and car development. All these efforts paid off with back-to-back wins in the SUZUKA 700km and 500km races in August in 2010 and 2011 respectively in SUPER GT. STI has decided to bring in the following concepts into the development of their sport parts: tuning and setups, which make motorsport vehicles fast, are in fact the same as settings for safe and enjoyable driving for road cars: and smooth driving, which makes the driver feel as if their driving skills have improved, is another ideal. Based on the concept that cars which improve driving skills are cars which can realise comfortable and fast cornering without any difficulties rather than those which are on the limit making the driver nervous, STI also began focusing on the development of complete cars which accommodate parts designed for a ‘flexible yet elegant driving feel'. This direction developed into the ‘Tuned by STI' series after 2007 and then the tS series. In the meantime, the S series - the ultimate complete car in which a ‘flexible yet elegant driving feel' concept was pushed from pillar to post, and the R series, which realises racing style driving, have both been introduced and appeal to many customers. (STI Subaru Tecnica International Inc) Intake Cams   In internal combustion engines with pistons, the camshaft is used to operate poppet valves. It then consists of a cylindrical rod running the length of the cylinder bank with a number of oblong lobes protruding from it, one for each valve. The cam lobes force the valves open by pressing on the valve, or on some intermediate mechanism as they rotate.
Material
Camshafts can be made out of several different types of material. These include:
Chilled iron castings: this is a good choice for high volume production. A chilled iron camshaft has a resistance against wear because the camshaft lobes have been chilled, generally making them harder. When making chilled iron castings, other elements are added to the iron before casting to make the material more suitable for its application.
Billet Steel: When a high quality camshaft is required, engine builders and camshaft manufacturers choose to make the camshaft from steel billet. This method is also used for low volume production. This is a much more time consuming process, and is generally more expensive than other methods. However the finished product is far superior. When making the camshaft, CNC lathes, CNC milling machines and CNC camshaft grinders will be used. Different types of steel bar can be used, one example being EN40b. When manufacturing a camshaft from EN40b, the camshaft will also be heat treated via gas nitriding, which changes the micro-structure of the material. It gives a surface hardness of 55-60 HRC. These types of camshafts can be used in high-performance engines.
Timing
A steel billet racing camshaft with noticeably broad lobes (very long duration)
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 the air/fuel mixture intake and exhaust gases, 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. Direct drive using gears is unusual because the frequently reversing torque caused by the slope of the cams tends to quickly wear out gear teeth. Where gears are used, they tend to be made from resilient fibre rather than metal, except in racing engines that have a high maintenance routine. Fibre gears have a short life span and must be replaced regularly, much like a cam belt. In some designs the camshaft also drives the distributor and the oil and fuel pumps. Some vehicles may have the power steering pump driven by the camshaft. With some early fuel injection systems, cams on the camshaft would operate the fuel injectors.
An alternative used in the early days of OHC engines was to drive the camshaft(s) via a vertical shaft with bevel gears at each end. This system was, for example, used on the pre-WW1 Peugeot and Mercedes Grand Prix cars. Another option was to use a triple eccentric with connecting rods; these were used on certain W.O. Bentley-designed engines and also on the Leyland Eight.
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 speed 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.
The timing of the camshaft can be advanced to produce better low RPM torque, or retarded for better high RPM power. Either of these moves the overall power produced by the engine down or up the RPM scale respectively. The amount of change is very little (usually < 5 deg), and affects valve to piston clearances.
Duration
Duration is the number of crankshaft degrees of engine rotation during which the valve is off the seat. As a generality, greater duration results in more horsepower. The RPM at which peak horsepower occurs is typically increased as duration increases at the expense of lower rpm efficiency (torque).[citation needed]
Duration can often be confusing because manufacturers may select any lift point to advertise a camshaft's duration and sometimes will manipulate these numbers. The power and idle characteristics of a camshaft rated at .006" will be much different than one rated the same at .002".
Many performance engine builders gauge a race profile's aggressiveness by looking at the duration at .020", .050" and .200". The .020" number determines how responsive the motor will be and how much low end torque the motor will make. The .050" number is used to estimate where peak power will occur, and the .200" number gives an estimate of the power potential.
A secondary effect of increase duration is increasing overlap, which is the number of crankshaft degrees during which both intake and exhaust valves are off their seats. It is overlap which most affects idle quality, inasmuch as the "blow-through" of the intake charge which occurs during overlap reduces engine efficiency, and is greatest during low RPM operation. In reality, increasing a camshaft's duration typically increases the overlap event, unless one spreads lobe centers between intake and exhaust valve lobe profiles.
Lift
The camshaft "lift" is the resultant net rise of the valve from its seat. The further the valve rises from its seat the more airflow can be released, which is generally more beneficial. Greater lift has some limitations. Firstly, the lift is limited by the increased proximity of the valve head to the piston crown and secondly greater effort is required to move the valve's springs to higher state of compression. Increased lift can also be limited by lobe clearance in the cylinder head construction, so higher lobes may not necessarily clear the framework of the cylinder head casing. Higher valve lift can have the same effect as increased duration where valve overlap is less desirable.
Higher lift allows accurate timing of airflow; although even by allowing a larger volume of air to pass in the relatively larger opening, the brevity of the typical duration with a higher lift cam results in less airflow than with a cam with lower lift but more duration, all else being equal. On forced induction motors this higher lift could yield better results than longer duration, particularly on the intake side. Notably though, higher lift has more potential problems than increased duration, in particular as valve train rpm rises which can result in more inefficient running or loss of torque.
Cams that have too high a resultant valve lift, and at high rpm, can result in what is called "valve bounce", where the valve spring tension is insufficient to keep the valve following the cam at its apex. This could also be as a result of a very steep rise of the lobe and short duration, where the valve is effectively shot off the end of the cam rather than have the valve follow the cams’ profile. This is typically what happens on a motor over rev. This is an occasion where the engine rpm exceeds the engine maximum design speed. The valve train is typically the limiting factor in determining the maximum rpm the engine can maintain either for a prolonged period or temporarily. Sometimes an over rev can cause engine failure where the valve stems become bent as a result of colliding with the piston crowns.
Position
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.
Number of camshafts
Main articles: overhead valve and overhead cam
While today some cheaper engines rely on a single camshaft per cylinder bank, which is known as a single overhead camshaft (SOHC), most[quantify] modern engine designs (the overhead-valve or OHV engine being largely obsolete on passenger vehicles), are driven by a two camshafts per cylinder bank arrangement (one camshaft for the intake valves and another for the exhaust valves); such camshaft arrangement is known as a double or dual overhead cam (DOHC), thus, a V engine, which has two separate cylinder banks, may have four camshafts (colloquially known as a quad-cam engine[6]).
More unusual is the modern W engine (also known as a 'VV' engine to distinguish itself from the pre-war W engines) that has four cylinder banks arranged in a "W" pattern with two pairs narrowly arranged with a 15-degree separation. Even when there are four cylinder banks (that would normally require a total of eight individual camshafts), the narrow-angle design allows the use of just four camshafts in total. For the Bugatti Veyron, which has a 16-cylinder W engine configuration, all the four camshafts are driving a total of 64 valves.
The overhead camshaft design adds more valvetrain components that ultimately incur in more complexity and higher manufacturing costs, but this is easily offset by many advantages over the older OHV design: multi-valve design, higher RPM limit and design freedom to better place valves, ignition (Spark-ignition engine) and intake/exhaust ports
(Wikipedia)
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Produktbeschreibung

STI  Subaru Tecnica International Inc. (STI) is a subsidiary of Fuji Heavy Industries Ltd. (FHI), which was established to undertake the motorsport activities of SUBARU. STI's core business is supplying motorsport base vehicles and competition parts and planning and developing SUBARU Limited Edition Models by applying special tuning techniques as well as planning and selling accessories and tuning parts to add variety to car life for auto enthusiasts worldwide. Through these operations, STI aims to provide its many SUBARU fans with special satisfaction. In 1972, FHI participated in the Southern Cross Rally in Australia with the first Japanese FF car - the Leone, before bringing out the Leone 4WD (the first AWD car in the WRC) in the Safari Rally in 1980. Following this, in order to respond to a new generation of motorsport with AWD turbo cars, which was expected to take off, STI was established in April 1988. Its founder and then president, the late Mr. Ryuichiro Kuze, was a board director of FHI and a co-driver in the Leone when it debuted in the Southern Cross Rally in 1972. As soon as he founded STI, he and his company planned and operated an event to challenge the world speed record in Arizona in the USA with the first Legacy which would herald in the future for SUBARU. In the event, the Legacy set a new world speed record for 100,000 consecutive kilometres of driving, a record which STI held for 16 years. This is how STI with its mission ‘to make SUBARU world number one', embarked on its journey as a brand which already was enjoying the world's number 1 title. After refining its AWD technology through a demanding Safari Rally, SUBARU began full-participation in the WRC with the Legacy, starting from Safari in 1990. STI's founder, Kuze teamed up with an up and coming British team to form the SUBARU World Rally Team the same year. Starting from the Acropolis Rally in Greece, the team competed under a new Japan-UK organisational structure, with the Japanese side in charge of engines and the British, the chassis. Meanwhile, STI's WRC activities for SUBARU led to the development of a car that could win in the WRC, and in 1992 this was finally embodied as a package - the Impreza. In the WRC, SUBARU clinched their first victory with the Legacy in New Zealand in 1993 before the succeeding Impreza came in 2nd outright in its debut event in Finland the same year. SUBARU made rapid progress after that. They finished the 1994 WRC in 2nd with 3 wins in the season. In 1995 and 96, they won rally after rally with an unstoppable force, and walked off with the WRC manufacturers' title for both years. As the World Rally Car regulation was newly enforced in 1997, the Impreza WRC, which had been developed in compliance with the new vehicle regulation, remarkably won 8 out of the season's 14 rallies that year to become the first Japanese car to be crowned as the WRC Manufacturers' Champion for three consecutive years. Released in November 1992, the Impreza was first used in the WRC in the mid stage of 1993. Although it already had 240PS as standard, it was required to introduce an evolution model to fight against formidable European rivals in the WRC. As a result, the WRX-STI was released in January 1994. Based on the WRX turbo model, WRX STI was equipped with forged pistons, a special ECU and larger muffler. With increased power to 250PS, this model was only built to order and the engine was fine-tuned by STI. Following a minor change in the Impreza in October 1994, an STI version was also released to much accolade. This STI Version featured the Drivers Control Centre Differential (DCCD) as well as a power increase to 275PS thanks to the reinforced cylinder heads and enhanced turbo boost pressure. Its success allowed the STI Version, which was then a limited edition model, to go into mass-production with its catalogue model from Version II in 1995 onward. Since then, the STI Version of the first Impreza - the GC8 type evolved into Version III featuring 280PS in 1996, and then up to Version VI released in 1999. While the Impreza STI Version, initially released as an evolution model for the WRC, continued to develop as a production car, STI planned a series of special specification models with even higher performance. The Impreza 22B STI Version, which was developed to celebrate SUBARU's three consecutive WRC Manufacturers' titles between 1995 and 97, was particularly revolutionary. Fitted with the same wide blister fender used in the Impreza World Rally Car, this model enjoyed a rush of orders upon its release in March 1998, and sold out immediately. As expected, this model enhanced the STI brand, and so STI took a big step forward towards its ideal - to become the figurehead for SUBARU. This direction of premium sport sedans in a limited number continued through the Impreza S201, which was released at the later stage of the GC8 type, and after the full model change of the Impreza in 2000, the S202, S203 and S204, which were all based on the GDB type Impreza. Following the full model change of the Impreza in 2000, the World Rally Car version's base was changed to the GDB type in 2001. Around that time, strong European manufacturers entered the World Rally Car field one after the other and the Impreza WRC improved its performance through competitions against these rivals. Driving the GDB type Impreza, Richard Burns became SUBARU's second WRC drivers' champion in 2001 - the GDB type Impreza's debut year, following Colin McRae in 1995. Then Petter Solberg won the championship behind the wheel of an Impreza, and proving the SUBARU is fast with anyone. SUBARU has won 47 WRC rallies - the most of any Japanese manufacturer; 46 of them in an Impreza, and so, this car now is known familiarly as a true world-class sport sedan among rally fans around the world. Furthermore, in another world championship, the PWRC where Group N cars of near-showroom specification compete, drivers in the Impreza won the title for 4 consecutive years from 2003, including a long-cherished world title for Japanese top rally driver Toshi Arai in 2005 - an achievement he then repeated in 2007. In rallying with Group N vehicles, which are closely based on their production model counterparts, victory cannot be guaranteed without good features in the original base model. While the Impreza WRX STI has established its position as a production model of FHI, STI's development department in close ties with FHI has introduced detailed specification changes at every annual revamp in order for the vehicle to be able to continually display high performance in rally competitions at a customer level. Consequently, the Impreza continued to make brilliant progress especially in the second half of 2000 in national and regional rally championships all around the world. In this way, the ever-evolving Impreza WRX STI consolidates and incorporates feedback and requests from the worldwide motorsport field. At the end of 2008, FHI announced its withdrawal from its WRC programme at a works team level. Following this decision, STI started to consider trying motorsport categories in which the company can capitalise on technologies and resources developed through the WRC to date. One idea was to continue offering their expertise to a GT300 vehicle in the Japanese SUPER GT series. Although racing conditions are different, challenges such as instantaneously delivering strong performance and maintaining durability and capability under harsh conditions are the same as in the WRC. Since the start of development of a new GT300 race car based on the Legacy in 2009, STI has utilised a string of ideas to develop the performance of the horizontally opposed turbo engine for a GT300 vehicle in conjunction with FHI and R&D SPORT which is in charge of team operations and car development. All these efforts paid off with back-to-back wins in the SUZUKA 700km and 500km races in August in 2010 and 2011 respectively in SUPER GT. STI has decided to bring in the following concepts into the development of their sport parts: tuning and setups, which make motorsport vehicles fast, are in fact the same as settings for safe and enjoyable driving for road cars: and smooth driving, which makes the driver feel as if their driving skills have improved, is another ideal. Based on the concept that cars which improve driving skills are cars which can realise comfortable and fast cornering without any difficulties rather than those which are on the limit making the driver nervous, STI also began focusing on the development of complete cars which accommodate parts designed for a ‘flexible yet elegant driving feel'. This direction developed into the ‘Tuned by STI' series after 2007 and then the tS series. In the meantime, the S series - the ultimate complete car in which a ‘flexible yet elegant driving feel' concept was pushed from pillar to post, and the R series, which realises racing style driving, have both been introduced and appeal to many customers. (STI Subaru Tecnica International Inc) Intake Cams   In internal combustion engines with pistons, the camshaft is used to operate poppet valves. It then consists of a cylindrical rod running the length of the cylinder bank with a number of oblong lobes protruding from it, one for each valve. The cam lobes force the valves open by pressing on the valve, or on some intermediate mechanism as they rotate.
Material
Camshafts can be made out of several different types of material. These include:
Chilled iron castings: this is a good choice for high volume production. A chilled iron camshaft has a resistance against wear because the camshaft lobes have been chilled, generally making them harder. When making chilled iron castings, other elements are added to the iron before casting to make the material more suitable for its application.
Billet Steel: When a high quality camshaft is required, engine builders and camshaft manufacturers choose to make the camshaft from steel billet. This method is also used for low volume production. This is a much more time consuming process, and is generally more expensive than other methods. However the finished product is far superior. When making the camshaft, CNC lathes, CNC milling machines and CNC camshaft grinders will be used. Different types of steel bar can be used, one example being EN40b. When manufacturing a camshaft from EN40b, the camshaft will also be heat treated via gas nitriding, which changes the micro-structure of the material. It gives a surface hardness of 55-60 HRC. These types of camshafts can be used in high-performance engines.
Timing
A steel billet racing camshaft with noticeably broad lobes (very long duration)
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 the air/fuel mixture intake and exhaust gases, 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. Direct drive using gears is unusual because the frequently reversing torque caused by the slope of the cams tends to quickly wear out gear teeth. Where gears are used, they tend to be made from resilient fibre rather than metal, except in racing engines that have a high maintenance routine. Fibre gears have a short life span and must be replaced regularly, much like a cam belt. In some designs the camshaft also drives the distributor and the oil and fuel pumps. Some vehicles may have the power steering pump driven by the camshaft. With some early fuel injection systems, cams on the camshaft would operate the fuel injectors.
An alternative used in the early days of OHC engines was to drive the camshaft(s) via a vertical shaft with bevel gears at each end. This system was, for example, used on the pre-WW1 Peugeot and Mercedes Grand Prix cars. Another option was to use a triple eccentric with connecting rods; these were used on certain W.O. Bentley-designed engines and also on the Leyland Eight.
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 speed 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.
The timing of the camshaft can be advanced to produce better low RPM torque, or retarded for better high RPM power. Either of these moves the overall power produced by the engine down or up the RPM scale respectively. The amount of change is very little (usually < 5 deg), and affects valve to piston clearances.
Duration
Duration is the number of crankshaft degrees of engine rotation during which the valve is off the seat. As a generality, greater duration results in more horsepower. The RPM at which peak horsepower occurs is typically increased as duration increases at the expense of lower rpm efficiency (torque).[citation needed]
Duration can often be confusing because manufacturers may select any lift point to advertise a camshaft's duration and sometimes will manipulate these numbers. The power and idle characteristics of a camshaft rated at .006" will be much different than one rated the same at .002".
Many performance engine builders gauge a race profile's aggressiveness by looking at the duration at .020", .050" and .200". The .020" number determines how responsive the motor will be and how much low end torque the motor will make. The .050" number is used to estimate where peak power will occur, and the .200" number gives an estimate of the power potential.
A secondary effect of increase duration is increasing overlap, which is the number of crankshaft degrees during which both intake and exhaust valves are off their seats. It is overlap which most affects idle quality, inasmuch as the "blow-through" of the intake charge which occurs during overlap reduces engine efficiency, and is greatest during low RPM operation. In reality, increasing a camshaft's duration typically increases the overlap event, unless one spreads lobe centers between intake and exhaust valve lobe profiles.
Lift
The camshaft "lift" is the resultant net rise of the valve from its seat. The further the valve rises from its seat the more airflow can be released, which is generally more beneficial. Greater lift has some limitations. Firstly, the lift is limited by the increased proximity of the valve head to the piston crown and secondly greater effort is required to move the valve's springs to higher state of compression. Increased lift can also be limited by lobe clearance in the cylinder head construction, so higher lobes may not necessarily clear the framework of the cylinder head casing. Higher valve lift can have the same effect as increased duration where valve overlap is less desirable.
Higher lift allows accurate timing of airflow; although even by allowing a larger volume of air to pass in the relatively larger opening, the brevity of the typical duration with a higher lift cam results in less airflow than with a cam with lower lift but more duration, all else being equal. On forced induction motors this higher lift could yield better results than longer duration, particularly on the intake side. Notably though, higher lift has more potential problems than increased duration, in particular as valve train rpm rises which can result in more inefficient running or loss of torque.
Cams that have too high a resultant valve lift, and at high rpm, can result in what is called "valve bounce", where the valve spring tension is insufficient to keep the valve following the cam at its apex. This could also be as a result of a very steep rise of the lobe and short duration, where the valve is effectively shot off the end of the cam rather than have the valve follow the cams’ profile. This is typically what happens on a motor over rev. This is an occasion where the engine rpm exceeds the engine maximum design speed. The valve train is typically the limiting factor in determining the maximum rpm the engine can maintain either for a prolonged period or temporarily. Sometimes an over rev can cause engine failure where the valve stems become bent as a result of colliding with the piston crowns.
Position
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.
Number of camshafts
Main articles: overhead valve and overhead cam
While today some cheaper engines rely on a single camshaft per cylinder bank, which is known as a single overhead camshaft (SOHC), most[quantify] modern engine designs (the overhead-valve or OHV engine being largely obsolete on passenger vehicles), are driven by a two camshafts per cylinder bank arrangement (one camshaft for the intake valves and another for the exhaust valves); such camshaft arrangement is known as a double or dual overhead cam (DOHC), thus, a V engine, which has two separate cylinder banks, may have four camshafts (colloquially known as a quad-cam engine[6]).
More unusual is the modern W engine (also known as a 'VV' engine to distinguish itself from the pre-war W engines) that has four cylinder banks arranged in a "W" pattern with two pairs narrowly arranged with a 15-degree separation. Even when there are four cylinder banks (that would normally require a total of eight individual camshafts), the narrow-angle design allows the use of just four camshafts in total. For the Bugatti Veyron, which has a 16-cylinder W engine configuration, all the four camshafts are driving a total of 64 valves.
The overhead camshaft design adds more valvetrain components that ultimately incur in more complexity and higher manufacturing costs, but this is easily offset by many advantages over the older OHV design: multi-valve design, higher RPM limit and design freedom to better place valves, ignition (Spark-ignition engine) and intake/exhaust ports
(Wikipedia)
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