Components of a pushrod valve actuation system

Picture of a V8 engine block (with intake manifold removed), showing the camshaft, pushrods, and rockers. A V8 engine is a V engine with eight cylinders mounted on the Crankcase in two banks of four cylinders in most cases set at a right angle to each other The cylinder block or engine block is a machined casting (or sometimes an assembly of modules containing cylindrically bored holes for the Pistons of a multi-cylinder In Automotive engineering, an intake manifold or inlet manifold is the part of an Engine that supplies the Fuel / Air mixture to

An overhead valve (OHV) engine, also called pushrod engine or I-head engine is a type of piston engine that places the camshaft in the cylinder block (usually beside and slightly above the crankshaft in a straight engine or directly above the crankshaft in the V of a V engine) and uses pushrods or rods to actuate rocker arms above the cylinder head to actuate the valves. A reciprocating engine, also often known as a piston engine, is a Heat engine that uses one or more reciprocating Pistons to convert The camshaft is an apparatus often used in Piston engines to operate Poppet valves It consists of a cylindrical rod running the length of the Cylinder bank The cylinder block or engine block is a machined casting (or sometimes an assembly of modules containing cylindrically bored holes for the Pistons of a multi-cylinder The crankshaft, sometimes casually abbreviated to crank, is the part of an Engine which translates reciprocating Linear Usually found in 4- and 6- cylinder configurations the straight engine (often designated Inline engines is an Internal-combustion engine with all cylinders A V engine is a common configuration for an Internal combustion engine. Generally referred to within the Internal combustion engine of automotive marine motorcycle and reciprocating aviation engines the rocker arm is a reciprocating lever In an Internal combustion engine, the cylinder head sits atop the cylinders and consists of a platform containing part of the Combustion chamber and the A poppet valve is a Valve consisting of a hole usually round or oval and a tapered plug usually a disk shape on the end of a shaft also called a valve stem Lifters or tappets reside in the engine block between the camshaft and pushrods. A tappet in Mechanical engineering is a projection which imparts a linear motion to some other component within an assembly

This contrasts with an overhead cam (OHC) design which places the camshaft(s) above the cylinder head and drives the valves directly or through short rocker arms. Overhead camshaft, commonly abbreviated to OHC, Valvetrain configurations place the engine Camshaft within the Cylinder heads above the In an OHC engine, the camshaft(s) are normally part of the cylinder head assembly, while in an I-head engine the camshaft (rarely more than one) is part of the main engine block assembly.

In 1949, Oldsmobile introduced the Rocket V8. Oldsmobile was a brand of Automobile produced for most of its existence by General Motors. The Oldsmobile Rocket V8 was the first post-war OHV V8 at General Motors. It was the first high-compression I-head design, and is the archetype for most modern pushrod engines. General Motors is the world's largest pushrod engine producer with engines such as the 3800 Series III Supercharged V6 (260 hp, 280 lbf·ft torque), LS7 Chevrolet Corvette 7. General Motors Corporation ( GM) ( is a multinational automobile manufacturer founded in 1908 and headquartered in the United States. The Buick V6, initially marketed as Fireball at its introduction in 1962 is a large V6 engine used by General Motors. A supercharger is an air compressor used for Forced induction of an Internal combustion engine. The foot-pound force, or simply foot-pound (symbol ft·lbf or ft·lb) is a unit of work or Energy (a scalar The LS series is a new design intended as the only V-8 engine utilized in General Motors ' line of RWD cars and trucks The Chevrolet Corvette is a Sports car that has been manufactured by General Motors since 1953 0 L V8 Engine (505 hp, 475 lbf·ft torque) and LS4 5. The LS series is a new design intended as the only V-8 engine utilized in General Motors ' line of RWD cars and trucks 3 L DOD V8 (303 hp, 323 lbf·ft torque). See the main article on Variable displacement for other similar systems Active Fuel Management (formerly known as Displacement on Demand Few pushrod type engines remain in production. This is a result of few manufacturers wanting to design both OHV and OHC engines. However, in 2002, Chrysler introduced a new pushrod engine: a 5. 7L Hemi engine. The new Chrysler Hemi engine presents advanced features such as variable displacement technology and has been a popular option with buyers. A Chrysler Hemi engine, known by the trademark Hemi, is an Internal combustion engine built by Chrysler that utilizes a hemispherical Variable displacement is an Automobile engine technology that allows the Engine displacement to change by deactivating cylinders, for improved Fuel The Hemi was on the Ward's 10 Best Engines list for 2003 through 2007. Ward's 10 Best Engines is an annual list of the ten "best" automobile engines available in the U Chrysler also produced the world's first production variable valve OHV engine with independent intake and exhaust phasing. The system is called CamInCam ^[1], and was first used in the 600hp SRT-10 engine for the 2008 Dodge Viper. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common The Dodge Viper is a V10 -powered Sports car manufactured by the Dodge division of Chrysler LLC.

History

In automotive engineering, an overhead valve internal combustion engine is one in which the intake and exhaust valves and ports are contained in the cylinder head. Modern automotive engineering is a branch of Vehicle engineering, incorporating elements of mechanical, electrical, electronic, software The internal combustion engine is an engine in which the Combustion of Fuel and an Oxidizer (typically air occurs in a confined space called a A poppet valve is a Valve consisting of a hole usually round or oval and a tapered plug usually a disk shape on the end of a shaft also called a valve stem In an Internal combustion engine, the cylinder head sits atop the cylinders and consists of a platform containing part of the Combustion chamber and the

The original overhead valve or OHV piston engine was developed by the Scottish-American David Dunbar Buick. A reciprocating engine, also often known as a piston engine, is a Heat engine that uses one or more reciprocating Pistons to convert Scottish Americans or Scots Americans are Citizens of the United States whose ancestry originates in Scotland. for the New Zealand politician see David Buick (New Zealand David Dunbar Buick was a Scottish -born American Inventor It employs pushrod-actuated valves parallel to the pistons and this is still in use today. An overhead valve (OHV engine, also called pushrod engine or I-head engine is a type of Piston engine that places the Camshaft A piston is a component of Reciprocating engines Pumps and Gas compressors It is located in a cylinder and is made gas-tight by Piston This contrasts with previous designs which made use of side valves and sleeve valves. A flathead engine or sidevalve engine (sometimes called a flatty) is an Internal combustion engine with valves placed in the engine block The sleeve valve is a type of Valve mechanism for Piston engines distinct from the more common Poppet valve.

Nowadays, side-valves have virtually disappeared (except perhaps in lawn-mower engines) and valves are almost all "overhead". However most are now driven more directly by the overhead camshaft system and these are designated OHC instead (either SOHC or DOHC). Overhead camshaft, commonly abbreviated to OHC, Valvetrain configurations place the engine Camshaft within the Cylinder heads above the Overhead camshaft, commonly abbreviated to OHC, Valvetrain configurations place the engine Camshaft within the Cylinder heads above the Overhead camshaft, commonly abbreviated to OHC, Valvetrain configurations place the engine Camshaft within the Cylinder heads above the

Pushrod engines have become less common in recent years, serving primarily as either truck engines or as budget V6 models for General Motors, though Chrysler's HEMI engines and GM's LS series are a notable exception. Pushrod engines are nearly extinct among other automakers.

Advantages

Pushrod engines have specific advantages:

• Smaller overall packaging - Because of the camshaft's location inside the engine block, pushrods are more compact than an overhead cam engine of comparable displacement. The cam-in-block Valvetrain layout of Piston engines is one where the Camshaft is placed within the Cylinder block, usually beside and slightly For example, Ford's 4. Ford Motor Company is an American Multinational corporation and the world's fourth largest automaker based on Worldwide vehicle sales, following 6 L OHC modular V8 is larger than the 5. The Modular engine is Ford Motor Company 's current high volume Overhead camshaft (OHC V8 and V10 gasoline engine family 0 L I-head Windsor V8 it replaced. The Windsor engine is a 90-degree Small-block V8 from Ford Motor Company. GM's 4. 6 L OHC Northstar V8 is slightly taller and wider than GM's larger displacement 5. The Premium V family of Automobile engines is General Motors ' modern 90° V engine architecture 7 to 7. 0 L I-head LS V8. The LS series is a new design intended as the only V-8 engine utilized in General Motors ' line of RWD cars and trucks The Ford Ka uses the venerable Kent Crossflow pushrod engine to fit under its low bonnet line. The Ford Ka is a City car from the Ford Motor Company marketed in Europe and elsewhere

• Less complex drive system - Pushrod engines have a less complex drive system to time the camshaft when compared with OHC engines. Overhead camshaft, commonly abbreviated to OHC, Valvetrain configurations place the engine Camshaft within the Cylinder heads above the Most OHC engines drive the camshaft or camshafts using a timing belt, a chain or multiple chains. Overhead camshaft, commonly abbreviated to OHC, Valvetrain configurations place the engine Camshaft within the Cylinder heads above the The camshaft is an apparatus often used in Piston engines to operate Poppet valves It consists of a cylindrical rod running the length of the Cylinder bank The camshaft is an apparatus often used in Piston engines to operate Poppet valves It consists of a cylindrical rod running the length of the Cylinder bank A timing belt, timing chain or cam belt is a part of an Internal combustion engine that controls the timing of the engine's valves. Roller chain or bush roller chain is the type of chain most commonly used for transmission of mechanical power on Bicycles Motorcycles Roller chain or bush roller chain is the type of chain most commonly used for transmission of mechanical power on Bicycles Motorcycles These systems require the use of tensioners which add some complexity to the engine. In contrast a pushrod engine has the camshaft positioned next to the crankshaft and can be run with a much smaller chain or even direct gear connection.

Limitations

Some specific problems that remain with pushrod engines:

• Limited engine speeds or RPM - Pushrod engines have more valvetrain moving parts thus more valvetrain inertia and mass, as a result they suffer more easily from valve "float" and may exhibit a tendency for the pushrods, if improperly designed, to flex or snap at high engine speeds. Therefore, pushrod engine designs cannot revolve ("rev") at engine speeds as high as OHC designs.

Modern pushrod engines are usually limited to about 6,000 RPM to 8,000 RPM in production vehicles and 9,000 RPM to 10,500 RPM in racing applications. In contrast, many modern OHC engines may have rev limits from 6,000 RPM to 9,000 RPM in road legal vehicles and up to 19,000 RPM in current Formula One race engines using pneumatic valve springs, a technology not viable in pushrod engines. Pneumatic valve springs are metal bellows filled with compressed air occupying roughly the same space of metal springs used to close valves in high-speed Internal High-revving pushrod engines are normally solid (mechanical) lifter designs, flat and roller. In 1969, Chevrolet offered a Corvette, Camaro Z28, and other models with a solid lifter cam pushrod V8 (the ZL1) that could rev to 8,000 RPM. Chevrolet (ˌʃɛvroʊˈleɪ - French origin (also known as Chevy) is a Brand of Automobile, produced by General Motors (GM The Chevrolet Camaro is a " Pony car " made in North America by the Chevrolet Motor Division of General Motors. The Volvo B18 and B20 engines can rev to more than 7,000 RPM with their solid lifter camshaft. This B18 was a Straight-4 Automobile engine produced by Volvo Cars from 1961 through 1968 However, the LS7 of the C6 Corvette Z06 is the first production hydraulic roller cam pushrod engine to have a redline of 7100 RPM.

• Limited cylinder head design flexibility - OHC engines benefit substantially from the use of multiple valves as well as much greater freedom of component placement and intake and exhaust port geometry. Overhead camshaft, commonly abbreviated to OHC, Valvetrain configurations place the engine Camshaft within the Cylinder heads above the In Automotive engineering, an engine is referred to as multi-valve (or multivalve) when each cylinder has more than two valves. Most modern pushrod engines have two valves per cylinder, while many OHC engines can have three, four or even five valves per cylinder to achieve greater power. Though multi-valve pushrod engines exist their use is somewhat limited due to their complexity and is mostly restricted to low and medium speed diesel engines. In pushrod engines the size and shape of the intake ports as well as the position of the valves are limited by the pushrods.

1994 Mercedes/Ilmor Indianapolis 500 engine

The Indy 500 race in Indianapolis each year bears some vestige of its original purpose as a proving ground for automobile manufacturers, in that it once gave an advantage in engine displacement to engines based on stock production engines, as distinct from out-and-out racing engines designed from scratch. The Indianapolis 500-Mile Race, often shortened to Indianapolis 500 or Indy 500, and historically known simply as "The 500" is an American One factor in identifying production engines from racing engines was the use of pushrods, rather than the overhead cams used on most modern racing engines; Mercedes-Benz realized before the 1994 race that they could very carefully tailor a purpose-built racing engine using pushrods to meet the requirements of the Indy rules and take advantage of the 'production based' loophole but still design it to be state of the racing art in all other ways, without any of the drawbacks of a real production-based engine. Year 1994 ( MCMXCIV) was a Common year starting on Saturday (link will display full 1994 Gregorian calendar) They entered this engine in 1994, and, as expected, dominated the race. After the race, the rules were changed in order to reduce the amount of boost pressure allowed to be supplied by the turbocharger. A turbocharger, or turbo, is an air Compressor used for forced-induction of an Internal combustion engine. A turbocharger, or turbo, is an air Compressor used for forced-induction of an Internal combustion engine. The inability of the engine to produce competitive power output after this change caused it to become obsolete after just the one race. Mercedes-Benz knew this beforehand, deciding that the cost of engine development was worth one win at Indianapolis.

Additional information

The following table is a comparison of various engine configurations and types. This table shows the comparison of some important features of engine design

Comparison of naturally-aspirated engines for race and road legal track day cars

See also

• Valvetrain
• Overhead camshaft
• Cam-in-block
• Flathead engine

References

External links

• Pushrod (OHV), SOHC and DOHC engine animated diagrams
• LS7 torque and power by rpm chart
• Ferrari Enzo: The Engine