HEMI engine
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Jibanjyoti samant
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20-09-2010, 02:16 PM


Hi. Iam JIbanjyoti Samant persuing B Tech in final year.I want a detail seminar and presentation report on HEMI engine.I hardly know anything about this topic and need to know the basics.
I expect to have a clear idea on this topic.Hope to get the desired information i am looking for.
ABSTRACT:
[/size][/font]A Chrysler Hemi engine, known by the trademark Hemi, is a series of V8 internal combustion engines built by Chrysler that utilize a hemispherical combustion chamber. A Chrysler Hemi engine, known by the trademark Hemi, is a series of V8 internal combustion engines built by Chrysler that utilize a hemispherical combustion chamber. three generations of hemi engines were built by chrysler for automobiles.
-Chrysler FirePower engine from 1951“1958
-The second one 1964“1971
-the third beginning in 2003

the valves of a two valve-per-cylinder engine to be angled rather than side-by-side due to the hemispherical combustion chamber. more space in the combustion chamber roof is thus created for the use of larger valves and also straightens the airflow passages through the cylinder head.the engine's airflow ("breathing") capacity is significantly improved thus improving the high power output from a given piston displacement. With a hemi combustion chamber, there is minimal quench and swirl to burn the fuel-air mix thoroughly and quickly.

FirePower with the OHV V8:
Using their military experience with the hemispherical combustion chambers, Chrysler decided to use this layout in their first OHV V8.
FirePower and FireDome were the nicknames of the different engine types here.

Hemi design reintroduced:
Hemi engines were produced only in less numbers for consumer sale due to their relatively high cost and poor street-use reputation[citation needed], the engine became legendary, with "Hemi" becoming one of the most familiar automobile-related words in the United States. In NHRA top fuel racing, the Hemi was usually equipped with a large Roots type supercharger.

Modern Hemi:
they are flatter and more complex shape than a truly hemi combustion chamber. . It uses a coil-on-plug distributorless ignition system and two spark plugs per cylinder to shorten flame travel . the 5.7 version is rated at approximately one horsepower per cubic inch. Multi-Displacement System (MDS) is used in some versions which can shut off two cylinders on each bank under light load to improve fuel economy.
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21-09-2010, 01:55 PM


More Info About HEMI engine


topicideashow-to-dyna-cam-engine?pid=23874
More Info About HEMI engine

topicideashow-to-chrysler-hemi-engine?pid=16915#pid16915
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18-10-2010, 09:32 AM


PRESENTED BY
SHASHANK VISHWAKARMA


.ppt   HEMI ENGINE.ppt (Size: 1.63 MB / Downloads: 455)


Introduction

Engines are the major components of any automobile. A user of an automobile wants to get maximum power output from the engine, at the same time, not sacrificing fuel efficiency. The design of an engine is very important. One of the most important parts of engine design is the design of the combustion chamber. Different types of combustion chamber heads are being used at present.
 
One type of chamber head is the hemispherical head. The hemispherical head design enables the user to extract more power from the engine. The engines using hemispherical heads are known as HEMI engines. Modern HEMI engines are using various developments that have come up in the recent past. This has enabled these engines to provide the user with additional advantages apart from serving its major purpose,,supplying more power.
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07-01-2011, 11:27 PM

ABSTRACT


Engines are the major components of any automobile. A user of an automobile wants to get maximum power output from the engine, at the same time, not sacrificing fuel efficiency.

The design of an engine is very important. One of the most important parts of engine design is the design of the combustion chamber. Different types of combustion chamber heads are being used at present.

One type of chamber head is the hemispherical head. The hemispherical head design enables the user to extract more power from the engine. The engines using hemispherical heads are known as HEMI engines.

Modern HEMI engines are using various developments that have come up in the recent past. This has enabled these engines to provide the user with additional advantages apart from serving its major purpose, ie, supplying more power.


.doc   hemi engines.doc (Size: 296 KB / Downloads: 207)

CONTENTS

Chapters Page No

1.0 INTRODUCTION 1
2.0 BASIC DESIGN 3
2.1 Flat Head Engine Design 3
2.2 Hemi Engine Design 5
3.0 MERITS AND DEMERITS 7
3.1 Merits 7
3.2 Demerits 8
4.0 RECENT DEVELOPMENTS 10
4.1 Supercharging 10
4.2 Cylinder De-activation 10
4.2.1 Specific Advantages 12
4.3 Twin Spark Plugs 14
5.0 CONCLUSION 15

List of figures

Fig 2.1: Flat head engine design 4
Fig 2.2: Hemi engine design 6
Fig 3.1: Hemi pentroof engine design 9


1.0 INTRODUCTION


Engine is the basic component of any automobile. Combustion engines may be divided into two general classes – internal combustion engines and external combustion engines.

In the external combustion engines, a working fluid is utilized to transfer some of the heat of combustion to that portion of the engine wherein this heat is transformed into mechanical energy.

The internal combustion engine inducts air from the atmosphere and the combustion of fuel and air occurs in or near that portion of the engine, which converts heat to mechanical energy.

Internal combustion engines may be further classified into reciprocating engines and non-reciprocating engines. Internal combustion engines may also be divided as spark ignition engines and compression ignition engines.

Spark ignition engines may work in a two-stroke cycle or a four-stroke cycle. The four strokes involved are

1) Intake stroke
2) Compression stroke
3) Power stroke
4) Exhaust stroke



Any two strokes of a four-stroke engine will be coupled in a two-stroke engine.

The HEMI engine is a four stroke, spark ignition, reciprocating type, internal combustion engine.

The design of the combustion chamber for a spark ignition engine has an important influence on the engine performance and its knocking characteristics. The design involves the shape of the combustion chamber, the location of the spark plug, and the location of the inlet and exhaust valves. The important requirements of a spark ignition engine combustion chamber are to provide higher power output with minimum octane requirement, high thermal efficiency and smooth engine operation.


2.0 BASIC DESIGN

The HEMI engine was first developed in 1951 by the Chrysler Corporation. The advantage of HEMI engine over other engines of the time was that it produced more power. The reason for this was the efficiency of the combustion chamber.

2.1 FLATHEAD ENGINE DESIGN

Most cars prior to the 1950’s used what was known as a flathead and many lawn-mower engines still use the flathead design today because it is less expensive to manufacture. In a flathead engine, the valves are in the block, rather then in the head and they open in a chamber beside the piston.

The head in a flathead engine (fig. 2.1) is extremely simple- it is a solid metal casting with a hole drilled in to accept the spark plug. The camshaft in the block pushes directly on the valve stems to open the valves, eliminating the need for push rods and rocker arms. Everything is simpler in the flathead engine. The problem with a flathead engine is its thermal efficiency.











Fig 2.1



2.2 HEMI ENGINE DESIGN

In a HEMI engine (fig. 2.2), the top of the combustion chamber is hemispherical. The combustion area in the head is shaped like half of a sphere. An engine like this is said to have “hemispherical heads”. In a HEMI head, the spark plug is normally located at the top of the combustion chamber and the valves open on opposite sides of the combustion chamber.


Fig 2.2


3.0 MERITS AND DEMERITS

3.1 MERITS
There are many different parts of an engine’s design that control or determine the amount of power you can extract from each combustion stroke.

You want to burn all the gas in the cylinder. If the design leaves any of the gas unburned, that is untapped energy.

You want the maximum cylinder pressure to occur when the crankshaft is at the right angle so that you can extract all of the energy from the pressure.

You want to waste as little as the engine’s energy as possible to suck air and fuel into the combustion chamber and pushing exhaust out.

You want to waste as little heat as possible to the head and the cylinder walls. Heat is one of the things creating pressure in the cylinder; so lost heat means lower peak pressures.

All these factors are satisfied in the HEMI engine because of its design. The last item in the list is one of the key advantages of the HEMI head versus the flat head engine. Surface area causes heat loss. Fuel that is near the head walls may be so cool that it does not burn efficiently. With a flat head, the amount of surface
area relative to volume of the combustion chamber is large. In a HEMI engine, surface area is much smaller than that in a flat head, and so less heat escapes and peak pressure can be higher.


Another factor with a HEMI head is the size of the valves. Since the valves are on the opposite sides of the head, there is more room for valves. The engine design that preceded the HEMI was a wedge shaped combustion chamber with the valves in line with each other. The in line arrangement limited valve size. In a HEMI engine, the valves can be large so that airflow through the engine is improved.
Thus, the HEMI engine delivers more power owing to its design. The design helps in attaining a high degree of turbulence (by inlet flow configuration or squish), high volumetric efficiency, improved anti-knock characteristics and compactness of combustion chamber.



3.2 DEMERITS

Not all engines are using HEMI heads though they have the advantages mentioned earlier. This is mainly because of two reasons.

One thing that a hemispherical head will never have is four valves per cylinder. The valve angles would be so crazy that the head would be nearly impossible to design. Having two valves per cylinder is not an issue in drag racing or NASCAR because racing engines are limited to two valves per cylinder in these categories. But on the street, four slightly smaller valves let an engine breath easier than two larger valves. Modern engines use a pentroof design (fig. 3.1) to accommodate four valves.



Another reason most high performance engines no longer use a HEMI design is the desire to create a smaller combustion chamber. Small chambers further reduce the heat lost during combustion and also shorten the distance the flame front has to travel during combustion. The compact pentroof design is helpful here as well.



Fig 3.1


4.0 RECENT DEVELOPMENTS

4.1 SUPERCHARGING

Supercharging is a method used to increase the density of air charge before it enters the cylinder. This allows more Oxygen for combustion than conventional methods. This results in better combustion and more power output.

In January 2003, the first supercharged HEMI engine was produced by Chrysler. It produces 430 horsepower and 480 lb-ft of torque, using the 5.7 Hemi engine and a Whipple supercharger.

4.2 CYLINDER DE-ACTIVATION

A new Mopar 5.7 litre 345 HEMI Magnum V-8 engine was developed recently. It is capable of producing a power of 345 hp at 5600 rpm and a torque of 375 lb-ft at 4400 rpm from 5.7 litres. A 6.1 litre version is being developed to be fitted in the Mercedes five-speed automatic to replace the current V-10 to obtain more power.

This engine featured cylinder de-activation using the multi-displacement system (MDS). The MDS turns off the fuel consumption in four cylinders when V-8 power is not needed. The system deactivates the valve lifters. This keeps the

valves in four cylinders closed, and there is no combustion. In addition to stopping combustion, energy is not lost by pumping air through these cylinders. This provides a world-class combination of power and fuel economy.

Customers will experience estimated fuel economy gains of up to 20 percent under various driving conditions, and a project and implimentationed 10 percent aggregate improvement. Improved fuel economy is realized without any change in customer experience—drivers will receive the benefit without changing their driving habits and without compromising style, comfort or convenience.

An LX engineer said that the Hemi was in part inspired by the slant six - in particular, the dual oiling circuit, with oil coming through the pushrods. This could maintain lubrication when cylinders are at rest.

It was found that only four cylinders were used during 17% of the suburban traffic portion of the test, during a full 48% of the freeway test which included "over 70 mph" speeds. Overall, they found that the engine powered down to four cylinders about 40% of the time. Non-enthusiast drivers may experience even more savings.

This engine is the first high volume, modern production vehicles in North America to feature fully functional cylinder de-activation. Owners get the power of HEMI engines and fuel economy of smaller or less powerful engines, when they use this system. This system should triumph where the Cadillac 4-6-8 failed because of the speed of modern electronic controls, the sophistication of the algorithms controlling the systems, and the use of electronic throttle control. The HEMI will be able to transition from eight cylinders to four in 40 milliseconds (0.04 seconds).





Bob Sheaves discussed multiple displacement on smaller engines:
"An Otto cycle engine requires 2 full revolutions of the crankshaft to fire all the cylinders. Therefore: 2 x 360=720 degrees of rotation. Divide that total rotation by the number of cylinders to have an even firing engine (naturally balanced) will give you: 120 degrees, which means that you have a cylinder firing every 120 degrees of rotation. Now, when you take out 3 of the cylinders, you have increased the firing rotation to 240 degrees (720/3), still balanced between each firing of a cylinder. The catch is that you have now increased the harmonic vibrations as the rpms increase. By deactivation of 4 cylinders in a V6, you no longer have a multiple of 6 that will keep the engine in primary balance. This is the reason balance shafts are often used in 90 degree V6s and inline 4 cylinder engines over 2.5L of displacement."

4.2.1 Specific Advantages

The cam was placed high up in the block to keep the pushrods as short as possible. The hollow cam has oversized journals and lobes to minimize side loading on the roller-style lifters. The valve springs are beehive types, more effective than standard springs so they can be lighter, with less lifter collapse. Rockers have much less inertial mass than usual, with the form and size carefully designed for a conservative .500 inches of lift; but the valves flow well enough to make this more than enough.

Generally, the engine appears to have been designed for lighter weight. The new Hemi is precision cast, which allows it to be lighter than a typical 5.7 litre engine, even with a taller deck height than Chevy's; and, partly to counter the inertia of its relatively long stroke, the pistons were made light as well, using cast eutectic alloy. The slipper-style piston has much in common with racing pistons, with a weight of 413 grams. For longevity, the Hemi pistons use a hard anodise on
the top ring land, to act as a heat barrier and anti-micro weld mix, and to allow the top ring to be only 3 mm from the top of the piston, cutting emissions while bringing more power. As with the old 426 Hemi, the rings are also relatively thin. Also in common with racing engines is a reservoir groove underneath the top ring, to reduce the pressure between the top and second ring. The cast iron block has a "meaty" deep-skirt design, with a crankshaft supported well by four bolts per main bearing (two vertical, two horizontal). The heads are aluminium, with the usual Chrysler plastic intake manifold.
The skirt is coated to allow for variance in production piston sizes, increase the fit for ring seal, and reduce piston noise. The lightweight wrist pin is also high-set.

The crank has larger inner counterweights than equivalent Chevy engines; but their weight is offset by the lighter pistons and rods. A windage tray sits underneath the crank, while the serpentine belt pulley also acts as a torsional vibration damper. The connecting rods are also designed for strength and low weight, using a powder metallurgy process first used by Porsche, and negating the need for a balance pad. A cap bolt is used instead of a through bolt.

One problem with the Hemi is that a speed density system is used for measuring air into the engine rather than air mass, so that cold air packages and such can throw the system off.
MDS saves about 3 mpg city, 3 mpg highway - that's by comparing original Chrysler 300C fuel mileage estimates with actual EPA figures.

According to Bob Lee, vice president of Powertrain Product Team, Chrysler Group, the MDS was a part of the engine's original design and hence resulted in a cylinder-deactivation system that is elegantly simple and completely integrated into the engine design. The benefits being fewer parts, maximum reliability and lower cost.

4.3 TWIN SPARK PLUGS

Each cylinder has an ignition coil pack over one spark plug, and a regular plug wire connected to the other spark plug. Further, the coil pack also has a plug wire attached to it that extends to the opposite cylinder bank. It appears that each cylinder shares a coil pack with another cylinder.

It appears that a separate coil fires each of the two plugs on a given cylinder. One plug has a coil directly attached, and the other is fired via an ignition wire connected to a coil located on another cylinder on the opposite bank. The benefits would be one-half the number of coils (8 vs. 16) compared to each plug having its own coil, and of course less weight.

There are two possibilities as to how the coils are fired. One is that the coils could contain two sets of windings that are insulated from each other and operate separately (one winding set for the plug directly underneath and another for the plug attached on the other bank). The other approach would be a coil with a single set of windings, and timing such that when the coil is firing a plug on the other bank, the cylinder under the coil would be on the exhaust stroke and that plug would fire also but with no effect.


5.0 CONCLUSION

Today's HEMI is that in name only. Nowadays HEMI pentroof engines, due to the disadvantages mentioned earlier, are replacing the HEMI engines. It is found that the power delivered by these engines is greater than the power output from engines with I-head, H-head, L-head, T-head, etc.

These engines are being used more and more in modern cars. Though Chrysler is the major user of this type of engines, other motor companies are also beginning to use these engines with some variations because of the patent protection that is present for these engines.
HEMI engines also find a major application in cars being used for racing purposes.

REFERENCES


1) Ganesan, V; “Internal Combustion Engines”
2) Gill, Paul W; Smith, James H; Ziurys, Eugene J; “Fundamentals of Internal Combustion Engines”
3) Overdrive, September 2003 issue

howstuffworks.com

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.ppt   HEMI PPT.ppt (Size: 333 KB / Downloads: 211)

Guided by,
Prof.V.M. KORDE

Submitted By:
Anup.V.Wakodikar


CONTENTS
Introduction to Engines

History Of HEMI Engines

Construction of HEMI Engines

Working of HEMI Engines

Comparison between HEMI and Flathead Engine

Advantages

Disadvantages

Modern users of HEMI


HISTORY OF “HEMI” ENGINES
6-Cylinder HEMI Engine was found by Harry Westlake in 1948

180 Horsepower HEMI V-8 Engine was found by Chrysler in 1951(“331 HEMI”)

In 1956 Chrysler reintroduced modified HEMI engine having displacement of 354 cubic inch

In 1957 Chrysler again introduced a HEMI engine having displacement of 392 cubic inch

In 1964 Chrysler introduced a 7-liter version having displacement of 426 cubic inch

In 1965 the 426 Street HEMI came out producing 425 horsepower

In 2002 Chrysler introduced HEMI Engine having valve and twin spark plug


CONSTRUCTION OF HEMI ENGINES

1.VALVE TRAIN:-The inlet and exhaust valves are located on opposite sides of the chamber at 90 degrees to the cylinder bank.

2.CYLINDER HEAD:-The cylinder head are shaped spherically, like the inside of a half cut ball. This allows for a symmetrical placement of bigger valves. the intake and exhaust valves are usually on opposite sides of the chamber, allowing for the combustion mixture to flow directly across the chamber, commonly referred to as "cross-flow" .The air-fuel mixture flows
through a Hemi chamber in a
straighter, less restrictive manner
than in a wedge-type chamber.
More mixture can also enter the
chamber for faster ignition, which
allows the engine to produce more
horsepower.

3.PISTONS:-All original pistons are cast
aluminium alloy. Most have slight
compression domes (area of slightly
smaller diameter than the bore)


4.CONNECTING ROD:-Each engine has
its own unique rod. All rods are high
quality forged steel, and more than
adequate in strength for the original
power produced.



5.CRANKSHAFT:-All crankshafts are high quality forged steel with rolled fillets, and use an un-threaded 8 bolt (obsolete pattern) flange.


WORKING OF HEMI ENGINES
Working of HEMI Engine is based on Otto cycle which consist of the following strokes. A stroke refers to the full travel of the piston from Top Dead Center (TDC) to Bottom Dead Center (BDC).

1.Intake Stroke:-On the intake or induction stroke of the piston , the piston descends from the top of the cylinder to the bottom of the cylinder, reducing the pressure inside the cylinder. A mixture of fuel and air is forced by atmospheric (or greater) pressure into the cylinder through the intake port. The intake valve(s) then close.

2.Compression stroke:-With both intake and exhaust valves closed, the piston returns to the top of the cylinder compressing the fuel-air mixture. This is known as the compression stroke.

3.Power stroke:-While the piston is close to Top Dead Center, the compressed air–fuel mixture is ignited, usually by a spark plug (for a gasoline or Otto cycle engine) or by the heat and pressure of compression (for a diesel cycle or compression ignition engine). The resulting massive pressure from the combustion of the compressed fuel-air mixture drives the piston back down toward bottom dead center with tremendous force. This is known as the power stroke, which is the main source of the engine's torque and power.

4.Exhaust stroke:-During the exhaust stroke, the piston once again returns to top dead center while the exhaust valve is open. This action evacuates the products of combustion from the cylinder by pushing the spent fuel-air mixture through the exhaust valve(s).

The intake (A) stroke is performed by an isobaric expansion, followed by the compression (B) stroke, performed by an adiabatic compression. Through the combustion of fuel an isochoric process is produced, followed by an adiabatic expansion, characterizing the power © stroke. The cycle is closed by an isochoric process and an isobaric compression, characterizing the exhaust (D) stroke.


ADVATAGES OF HEMI ENGINES
In a HEMI engine, valves can be large so the airflow through the engine is improved.
The air-fuel mixture flows through a Hemi chamber in a straighter, less restrictive manner
With the hemispherical combustion chamber design, the intake and exhaust valves are usually on opposite sides of the chamber, allowing for the combustion mixture to flow directly across the chamber
In a spherical design, the size of the valves can be much larger. The larger the valves, the larger their corresponding openings during the 4-stroke combustion process. That translates into more airflow.
A HEMI engine has less surface area than a conventional flat head engine. That means the fuel within the chamber burns more efficiently because less heat is lost to the limited surface area.


DISADVANTAGES OF HEMI ENGINES
The main drawback to a HEMI engine is the number of valves it allows per cylinder. Because the top of the chamber is shaped like a sphere, it can only fit two valves

Expensive to produce

The pistons are heavy (high reciprocating mass) and the large dome shrouded spark plugs and valves, requiring more ignition timing and increasing hydrocarbon emissions




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HISTORY
Hemispherical combustion chambers, which had been used for centuries in mortars and cannons were introduced on some of the earliest automotive engines, shortly after proving the concept of internal combustion engines themselves.
Hemispherical cylinder heads have been used since at least 1901, they were used by the Belgian car maker Pipe in 1905, the Peugeot Grand Prix Car of 1912, the Alfa Romeo GP car of 1914, Daimler, and Riley. Stutz built four valve engines, conceptually anticipating modern car engines. The BMW double push rod design, taken over by Bristol Cars, the Peugeot 403, the Toyota T engine and Harry Arminius Miller racing engines are other examples.
In automotive engineering, an overhead valve internal combustion engine is one in which the intake and exhaust valves and ports are contained within the cylinder head.
The original overhead valve or OHV piston engine was developed by the Scottish-American David Dunbar Buick. It employs pushrod-actuated valves parallel to the pistons, and this is still in use today. This contrasts with previous designs which made use of side valves and sleeve valves.
Nowadays, automotive use of side-valves has virtually disappeared, 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 single overhead camshaft (SOHC) or double overhead camshaft (DOHC).
WORKING
A hemi engine refers to the way the pistons, heads and block are designed. This style of engine claims to provide a better flow of air inside the cylinder by creating more room for larger valves in turn providing more power. The chamber on a hemi is hemispherical instead of being flat like traditional engines. This shape provides more surface area on the block allowing room for the larger valves. When the engine can breath better there is less friction and more clean air / fuel mixture providing more power. However, this chamber is very tall so the pistons must be domed to provide adequate compression. While the engine provides larger valves, the new design of the piston actually interferes with the air flow. With the domed pistons it is less likely to evenly distribute the air / fuel mixture, and to adequately remove the exhaust.
BENEFITS
Although a wedge-head design offers simplified valve actuation, it usually requires the air/fuel mixture to make sharp turns en route to and from the chamber. With a hemispherical chamber, larger valves are possible and a straighter, less restrictive flow path can be provided for the air/fuel mixture. This improves engine breathing. Placing the spark plug near the center of the chamber aids in achieving complete combustion of the fuel/air mixture, though it is not mandatory.
USAGE
Many of today's engines use active combustion chambers designed to tumble and swirl the fuel/air mix within the chamber for the most efficient combustion event possible. These active chambers usually look like kidney beans or two merged small 'hemi' areas surrounded by flat quenching areas over the pistons. By the end of the 1970s, development of engines utilizing true hemispherical chambers had ceased around the world; it had been gradually displaced by dramatically improved newer engine designs. Today, "hemi" is more of a trademark than a description of a combustion chamber.
The valves of a two valve-per-cylinder engine to be angled rather than side-by-side due to the hemispherical combustion chamber. more space in the combustion chamber roof is thus created for the use of larger valves and also straightens the airflow passages through the cylinder head the engine's airflow ("breathing") capacity is significantly improved thus improving the high power output from a given piston displacement. With a hemi combustion chamber, there is minimal quench and swirl to burn the fuel-air mix thoroughly and quickly.
OVERHEAD VALVE
An overhead valve (OHV) engine, also informally called pushrod engine or I-head engine, is a type of piston engine that places the camshaft within 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. Lifters or tappets are located in the engine block between the camshaft and pushrods. The more modern overhead camshaft (OHC) design (still literally overhead valve) avoids the use of pushrods by putting the camshaft in the cylinder head.
In 1949, Oldsmobile introduced the Rocket V8. 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, producing both V6 and V8 pushrod engines.
Few pushrod type engines remain in production outside of the United States market, and even American manufacturer Ford no longer offers pushrod engines in new vehicles. This is in part a result of some countries passing laws to tax engines based on displacement, due to the fact that displacement is somewhat related to the emissions and fuel efficiency of an automobile. This has given OHC engines a regulatory advantage in those countries, which resulted in few manufacturers wanting to design both OHV and OHC engines
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Submitted by
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HEMI engines
INTRODUCTION

Engines are the major components of any automobile. A user of an automobile wants to get maximum power output from the engine, at the same time, not sacrificing fuel efficiency. The design of an engine is very important. One of the most important parts of engine design is the design of the combustion chamber. Different types of combustion chamber heads are being used at present.
One type of chamber head is the hemispherical head. The hemispherical head design enables the user to extract more power from the engine. The engines using hemispherical heads are known as HEMI engines.Modern HEMI engines are using various developments that have come up in the recent past. This has enabled these engines to provide the user with additional advantages apart from serving its major purpose, ie, supplying more power.
Engine is the basic component of any automobile. Combustion engines may be divided into two general classes - internal combustion engines and external combustion engines.In the external combustion engines, a working fluid is utilized to transfer some of the heat of combustion to that portion of the engine wherein this heat is transformed into mechanical energy.
The internal combustion engine inducts air from the atmosphere and the combustion of fuel and air occurs in or near that portion of the engine, which converts heat to mechanical energy. Internal combustion engines may be further classified into reciprocating engines and non-reciprocating engines. Internal combustion engines may also be divided as spark ignition engines and compression ignition engines.
Spark ignition engines may work in a two-stroke cycle or a four-stroke cycle. The four strokes involved are
1) Intake stroke
2) Compression stroke
3) Power stroke
4) Exhaust stroke
The design of the combustion chamber for a spark ignition engine has an important influence on the engine performance and its knocking characteristics. The design involves the shape of the combustion chamber, the location of the spark plug, and the location of the inlet and exhaust valves. The important requirements of a spark ignition engine combustion chamber are to provide higher power output with minimum octane requirement, high thermal efficiency and smooth engine operation.
BASIC DESIGN
The HEMI engine was first developed in 1951 by the Chrysler Corporation. The advantage of HEMI engine over other engines of the time was that it produced more power. The reason for this was the efficiency of the combustion chamber.

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HEMI ENGINE
INTRODUCTION

Engine is the basic component of any automobile.
Combustion engines may be divided into two general classes
Internal combustion engines.
External combustion engines.
Hemi engine is a four stroke , spark ignition, reciprocating type, internal combustion engines
BASIC DESIGN
The HEMI engine was first developed in1951 by the chrysler corporation.
The advantage of HEMI engine over other engines of the time was that it produced more power.
The reason for this was the efficiency of the combustion chamber.
BASIC FLAHEAD ENGINE DEAIGN
HEMI ENGINE DESIGN

In a HEMI engine, the top of the combustion chamber is hemispherical.
The combustion area in the head shaped like half of a sphere.
An engine like this is said to have “hemispherical heads”.
In a HEMI head, the spark plug is normally located at the top of the combustion chamber and the valves open on opposite side of the combustion chamber.
BASIC HEMI ENGINE DESIGN
MERITS AND DEMERITS
MERITS

There are many different pats of an engine design that control or determine the amount of power you can extract from each combustion stroke.
You want to burn all the gas in the cylinder. If the design leaves any of the gas unburned , that is untapped energy.
You want the maximum cylinder pressure to occur when the crankshaft is at the right angle so that you can extract all of the energy from the pressure.
You want to waste as little as the engines energy as possible to suck air and fuel into the combustion chamber and pushing exhaust out.
You want to waste as little as the engines energy as possible to suck air and fuel into the combustion chamber and pushing exhaust out.
You want to waste as little as possible to the head and the cylinder walls.
Heat is one of the things creating pressure in the cylinder;
So lost heat means lower peak pressure.
All these factors are satisfied in the HEMI engine because of its design.
In a HEMI engine , surface area is much smaller than that in a flat head ,
And so less heat escapes and peak pressure can be higher
Another factor with a HEMI head is the size of the valves .
Since the valve are on the opposite sides of the head ,
There is more room for valve .
The engine design that preceded the HEMI was a wedge shaped combustion chamber with the valve in line with each other.
The in line arrangement with limmited valve size.
In the HEMI engine the valve can be large .
So that airflow through the engine is improvrd.
Thus the HEMI engine delivers more power owing to its design .
The design helps in attaining a higher degree of turbulence.
High volumetric efficiency, improved anti-knock characteristic and compactness of combustion chamber.
DEMERITS
Not all engines are using HEMI heads though they have the advantages mentioned .
This is mainly because of two reason.
One thing that a hemispherical head will never have is four valve per cylinder.
Another reason most high performance engines no longer use a HEMI design is the desire to create a smaller combustion chamber
PENTROOF HEMI ENGINE DESIGN
RECENT DEVELOPMENTS
SUPERCHARGING

Supercharging is a method used to increase the density of air charge before it enters the cylinder. This allows more Oxygen for combustion than conventional methods. This results in better combustion and more power output.
CYLINDER DE-ACTIVATION
This engine featured cylinder de-activation using the multi-displacement system (MDS). The MDS turns off the fuel consumption in four cylinders when V-8 power is not needed. The system deactivates the valve lifters. This keeps the
  valves in four cylinders closed, and there is no combustion. In addition to stopping combustion, energy is not lost by pumping air through these cylinders. This provides a world-class combination of power and fuel economy.
Specific Advantages
Generally, the engine appears to have been designed for lighter weight.
The new Hemi is precision cast, which allows it to be lighter than a typical 5.7 litre engine, even with a taller deck height than Chevy's; and, partly to counter the inertia of its relatively long stroke, the pistons were made light as well, using cast eutectic alloy
The skirt is coated to allow for variance in production piston sizes, increase the fit for ring seal, and reduce piston noise.
The lightweight wrist pin is also high-set
TWIN SPARK PLUGS
Each cylinder has an ignition coil pack over one spark plug, and a regular plug wire connected to the other spark plug. Further, the coil pack also has a plug wire attached to it that extends to the opposite cylinder bank. It appears that each cylinder shares a coil pack with another cylinder
CONCLUSION
It is found that the power deliver by these engines Is greater then the power output from engine with i-head , h-head , l-head , t-head.
These engine are used in more and more in modern cars.
Though chrysler is the major user of this type of engines, other motor companies are also beginning to use these engines with some variations because of the patent protection that is present for these engines.
hemi engines also find in major application in car being used for racing purposes.
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30-07-2012, 11:49 AM

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