Engines How They Work

 Bearings in internal combustion engines

Internal combustion engine

Internal combustion engine is a device converting the energy of a fuel-air mixture burning within a combustion chamber into mechanical energy.

Reciprocating internal combustion engine is an engine, in which burning process occurs within a cylinder equipped with a piston driven by the pressure of the combustion gases. The gas pressure force is transmitted to the crankshaft linked to the piston by means of a connecting rod. Such mechanical device called crank mechanism transforms the alternating linear motion of the piston into the rotation of the shaft.

Reciprocating engines are the most common type of internal combustion engines.

The figure below presents a scheme of a typical four-stroke reciprocating combustion engine.

The engine consists of four cylinders in different phases of the engine cycle (intake, compression, expansion and exhaust). Each cylinder has an inlet and exhaust valves, opening and closing of which is controlled by the cam mechanism.
Each piston is joined to the crank pin of the crankshaft though the connecting rod.

Internal combustion engine.png 

The four-stroke cycle:

  • Intake: The intake valve is open. The piston moves downwards from the Top Dead Center (TDC) to the Bottom Dead Center (BDC) sucking the fuel-air mixture into the cylinder.
  • Compression: Both valves are closed. The piston moves from BDC towards TDC compressing the gaseous fuel-air mixture. The compression causes pressure and temperature increase of the gas in the cylinder. When the crankshaft reaches some angle before TDC the fuel-air mixture is ignited and fuel combustion starts. Combustion further increases the gas pressure and temperature. In the gasoline (petrol) engines ignition is as a result of a spark produced by the spark plug. The engines of such type are called Spark Ignition (SI) engines. In the diesel engines the fuel-air mixture is ignited by the heat of the compressed gages. The engines of such type are called Compression Ignition (CI) engines.
  • Power (expansion): Both valves are closed. The piston travels from TDC to BDC under the high pressure of hot burning gases. The power of the the gases is transmitted to the crankshaft through the connecting rod. Just before the piston reaches the Bottom Dead Center the exhaust valve opens.
  • Exhaust: The exhaust valve is open. The piston moves towards TDC forcing the combustion gases out of the cylinder. When it reaches TDC the exhaust valve closes and the intake valve opens - the cycle returns to the initial state.

Functions of bearings in internal combustion engines

Bearings types.pngBearing is a device supporting a mechanical element and providing its movement relatively to another element with minimum power loss.

The rotating components of internal combustion engines are equipped with sleeve type sliding bearings.
The reciprocating engines are characterized by cycling loading of their parts including bearings. Such character of the loads is a result of alternating pressure of combustion gases in the cylinders.
Rolling bearings, in which a load is transmitted by rolls (balls) to a relatively small area of the ring surface, can not withstand under the loading conditions of internal combustion engines.
Only sliding bearings providing a distribution of the applied load over a relatively wide area may work in internal combustion engines.

The sliding bearings used in internal combustion engines:

  • Main crankshaft bearings support crankshaft providing its rotation under inertia forces generated by the parts of the shaft and oscillating forces transmitted by the connecting rods. Main bearings are mounted in the crankcase. A main bearing consists of two parts: upper and lower. The upper part of a main bearing commonly has an oil groove on the inner surface. A main bearing has a hole for passing oil to the feed holes in the crankshaft. Some of main bearings may have thrust bearing elements supporting axial loads and preventing movements along the crankshaft axis. Main bearings of such type are called flange main bearings.
  • Connecting rod bearings provide rotating motion of the crank pin within the connecting rod, which transmits cycling loads applied to the piston. Connecting rod bearings are mounted in the Big end of the connecting rod. A bearing consists of two parts (commonly interchangeable).
  • Small end bushes provide relative motion of the piston relatively to the connecting rod joined to the piston by the piston pin (gudgeon pin). End bushes are mounted in the Small end of the connecting rod. Small end bushes are cycling loaded by the piston pushed by the alternating pressure of the combustion gases.
  • Camshaft bearings support camshaft and provide its rotation.

Lubrication of the bearings in internal combustion engine

Purposes of lubrication of engine bearings are as follows:

  • significant decrease of the coefficient of friction;
  • extraction of the heat generated by the friction;
  • removal of foreign particles from the rubbing surfaces.


Engine bearings generally work in hydrodynamic regimes of friction.
Hydrodynamic friction implies the presence of a continuous lubricant film between the bearing and journal surfaces (Hydrodynamic journal bearing).

Constant supply of a lubricant (oil) in sufficient amounts is necessary for normal work of engine bearings.
Bearings lubrication is provided by the lubrication system. 

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VW ENGINE CODES

Engine Code

Displacement (cc)/Cyl

Bore (mm)

Stroke (mm)

Cylinder Head

CR

Horsepower

Torque

Injection

FC/FG

1471 I-4

76.5

80.0

8V Mechanical

8.2:1

71@5800

80@3500

Carb

FN

1588 I-4

79.5

80.0

8V Mechanical

8.2:1

71@5600

82@3000

Carb

EE/EF/EJ

1588 I-4

79.5

80.0

8V Mechanical

8.2:1

78@5500

83@3200

K-Jetronic

EH

1457 I-4

79.5

73.4

8V Mechanical

8.0:1

71@5800

73@3500

K-Jetronic

EN

1715 I-4

79.5

86.4

8V Mechanical

8.2:1

74@5000

90@3000

K-Jetronic

JH

1781 I-4

81.0

86.4

8V Mechanical

8.5:1

90@5500

105@3000

K-Jetronic

GX

1781 I-4

81.0

86.4

8V Hydraulic

9.0:1

85@5250

96@3000

K-Jetronic

HT

1781 I-4

81.0

86.4

8V Hydraulic

10.0:1

100@5500

105@3000

KE-Jetronic

RD

1781 I-4

81.0

86.4

8V Hydraulic

9.0:1

102@5250

110@3250

KE-Jetronic

RV

1781 I-4

81.0

86.4

8V Hydraulic

10.0:1

100@5400

109@3800

DigifantII

PF

1781 I-4

81.0

86.4

8V Hydraulic

10.0:1

105@5400

114@3800

Digifant II

PL

1781 I-4

81.0

86.4

16V Hydraulic

10.0:1

123@5800

120@4250

KE-Jetronic

9A

1984 I-4

82.5

92.8

16V Hydraulic

10.0:1

134@5800

133@4400

KE-Motronic

PG

1781 I-4 Supercharged

81.0

86.4

8V Hydraulic

8.0:1

158@5600

166@4000

Digifant I

AAA

2792 VR6

81.0

90.3

12V Hydraulic

10.0:1

178@5800

173@4200

Motronic

AAA

2792 VR6

81.0

90.3

12V Hydraulic

10.0:1

172@5800

173@4200

Motronic

AFP

2792 VR6

81.0

90.3

12V Hydraulic

10.5:1

174@5800

181@3200

Motronic

BDF

2792 VR6

81.0

90.3

24V Hydraulic

10.8:1

200@6200

195@3200

Motronic

BJS

3189 VR6

84.0

95.9

24V Hydraulic

11.3:1

240@6250

236@2800

Motronic

ABA

1984 I-4

82.5

92.8

8V Hydraulic

10.0:1

115@5400

122@3200

Motronic

AEG/AVH/AZG

1984 I-4

82.5

92.8

8V Hydraulic

10.0:1

115@5600

122@2600

Motronic

APH/AWD

1781 I-4 Turbo

81.0

86.4

20V Hydraulic

9.5:1

150@5700

155@1750-4600

Motronic

AWW

1781 I-4 Turbo

81.0

86.4

20V Hydraulic

9.3:1

150@5700

162@1950-5000

Motronic

AWP

1781 I-4 Turbo

81.0

86.4

20V Hydraulic

9.5:1

180@5500

173@1950-5000

Motronic

AEB/ATW

1781 I-4 Turbo

81.0

86.4

20V Hydraulic

9.5:1

150@5700

155@1750-4600

Motronic

AUG

1781 I-4 Turbo

81.0

86.4

20V Hydraulic

9.3:1

150@5700

155@1750-4600

Motronic

AWM

1781 I-4 Turbo

81.0

86.4

20V Hydraulic

9.3:1

170@5900

166@1950-5000

Motronic

AHA/ATQ

2771 V6

82.5

86.4

30V Hydraulic

10.6:1

190@6000

207@3200

Motronic

BDP

3999 W8

84.0

90.0

32V Hydraulic

10.8:1

270@6000

272@3250

Motronic

BGH

4172 V8

84.5

93.0

40V Hydraulic

11.0:1

335@6500

317@3500

Motronic

BRP

5998 W12

84.0

90.0

48V Hydraulic

10.8:1

420@6000

406@3250

Motronic

BPY

1984 I-4 Turbo

82.5

92.8

16V Hydraulic

10.3:1

200@5500

207@1800-4700

Motronic FSI

BGQ

2480 I-5

82.5

92.8

20V Hydraulic

9.5:1

150@5000

170@3750

Motronic

BLV

3598 VR6

89.0

96.4

24V Hydraulic

12.0:1

280@6200

265@2750

Motronic FSI

 

Watercooled Volkswagen Engines

8v Engines - Inline 4 Cylinder, Gasoline, 2 valves per cylinder
Code(L)FI TypeHorsepowerTorque @ RPMCompBoreStrokeCCS/CNotes
2H1.8LDigifant II94 @ 5400100 @ 300010:0:181.086.41781NoCabriolet from 90-93
ABA2.0LMotronic M5.9115 @ 5400122 @ 22009.0:182.592.781984NoBase Jetta Golf mk3 mk4
ABG1.8LDigifant II83 @ ?????? @ ???? 81.086.41781No90-93 Fox
AEG2.0LMotronic115 @ 5200122 @ 2600    No 
AVH2.0LMotronic      No 
AZG2.0LMotronic      No 
BBW2.0LMotronic      No 
BEV2.0LMotronicNo
DH1.9LCIS      No 
EH1.5LCIS71 @ 580073 @ 3500    No78-79 1.5L
EJ1.6LCIS78 @ 550083 @ 32008.0:179.580.01588No1980 FI 1.6L
EN1.7LCIS74 @ 500090 @ 30008.2:179.586.41715No1.7L FI 82-84
FX1.5LCarburetor62 @ ????76.6 @ 30008.0:179.573.41457No 
GX1.8LCIS/CIS-E85 @ 525096 @ 30009.0:181.086.41781NoFox
HT1.8LCIS-E100 @ 5500105 @ 300010.0:181.086.41781NoGTI, Jetta GLI (1985)
JF1.7LCarburetor      NoRabbit
JH1.8LCIS94 @ 5500102 @ 30008.5:181.086.41781NoScirocco 2
JN1.8LCIS      No 
MV2.1LCIS      No 
MZ1.8LCIS90 @ 550098 @ 3250 81.086.41781No85-86 Golf Jetta
PF1.8LDigifant II105 @ 5400114 @ 380010.0:181.086.41781No87-92 G J GTI
PG1.8LDigifant I158 @ ??????? @ ???? 81.086.41781YesCorrado G60, Passat G60
RD1.8LCIS-E102 @ 5250110 @ 325010.0:181.086.41781NoGTI, Jetta GLI
RV1.8LDigifant II100 @ 5400109 @ 380010.0:181.086.41781NoDigifant I in california
UM1.8LCIS      No 
WL1.7LSolex 1B1 carb70 @ 500093 @ 28007.3:179.586.51718NoIltis 1.7L low quality fuel
WT1.7LCIS      No 
XR1.5LCIS      No 
XS1.5LCIS      No 
XV1.5LCIS      No 
XW1.5LCIS      No 
XY1.5LCIS      No 
XZ1.5LCIS      No 
YG1.6LCIS      No 
YH1.6LCIS      No 
YK1.6LCIS      No 
YX1.7LSolex 1B1 carb75 @ 5000100 @ 28008.2:179.586.51718NoIltis 1.7L Gasoline
           

All Diesel IDI and TDI engines (Includes V10)

CodeCylValves(L)FI TypeEngine LayoutHorsepowerTorque @ RPMCompBoreStrokeCCTurboNotes
1V421.6LIndirect DieselInline59 @ 450081 @ 240023.0:176.586.41588Yes 
1Z421.9LDirect DieselInline90 @ 4000155 @ 180019.5:179.595.51896YesTDI
AAZ421.9LIndirect DieselInline75 @ 4200107 @ 240022.5:179.586.5 Yes1.8TD Canada only
AHU421.9LDirect DieselInline90 @ 4000155 @ 180019.5:179.595.51896YesTDI
ALH421.9LDirect DieselInline90 @ 4000155 @ 180019.5:179.595.51896YesTDI
BEW421.8LDirect DieselInline      Yes 
BKW1025.0LDirect DieselV310 @ 3750553 @ 200018.0:181.095.54921YesTouareg V10 TDI
CK421.5LIndirect DieselInline48 @ 500058 @ 250023.5:176.580.01471No1.5 NA Diesel
CR421.6LIndirect DieselInline52 @ 480071 @ 250023.0:176.586.41588No1.6 NA Diesel
CY421.6LIndirect DieselInline68 @ 450098 @ 250023.0:176.586.41588Yes1.6 TD
JK421.6LIndirect DieselInline52 @ 480071 @ 250023.0:176.586.41588No1.6 NA Diesel
MD421.6LIndirect DieselInline      No 
ME421.6LIndirect DieselInline52 @ 480068 @ 450023.0:176.586.41588No 
MF421.6LIndirect DieselInline68 @ 450098 @ 250023.0:176.586.41588Yes1.6 TD
              

16v Engines - Inline 4 Cylinder, Gasoline, 4 valves per cylinder

Code(L)FI TypeHorsepowerTorque @ RPMCompBoreStrokeCCTurboNotes
9A2.0LCIS-E/Motronic134 @ 5800133 @ 440010.0:182.586.41984No2.0 16V Passat
PL1.8LCIS-E123 @ 5800120 @ 425010.0:181.086.41781No16v Scirocco, GTI
??2.0LMotronic200 @ 5500207 @ 180010.3:182.586.41984YesMkV GTI, MkV Jetta GLI *NEW*

VR6 Engines - 15 degree V-Inline 6 cylinder Gasoline Engine

CodeValves(L)FI TypeHorsepowerTorque @ RPMCompBoreStrokeCCNotes
AAA22.8LMotronic M2.9172 @ ??????? @ ????10.0:181.090.02783First VR6
AFP22.8LMotronic       
BDF42.8LMotronic






BJS43.2LMotronic240 @ 6250236 @ 280011.3:184.096.03189VR6 from R32
           

1.8T Engines - Inline 4 Cylinder, Gasoline, 5 valves per cylinder, with Turbo

CodeCylFuel TypeValves(L)FI TypeEngine LayoutHorsepowerTorque @ RPMCompBoreStrokeCCS/CTurboNotes
AEB4Gasoline51.8LMotronicInline   81.086.41781NoNo 
APH4Gasoline51.8LMotronicInline  9.5:181.086.41781NoYes 
ATW4Gasoline51.8LMotronicInline   81.086.41781NoYes 
AUG4Gasoline51.8LMotronicInline   81.086.41781NoYes 
AVW4Gasoline51.8LMotronicInline   81.086.41781NoYes 
AWD4Gasoline51.8LMotronicInline  9.5:181.086.41781NoYes2000 Model Year
AWM4Gasoline51.8LMotronicInline   81.086.41781NoYes 
AWP4Gasoline51.8LMotronicInline  9.5:181.086.41781NoYes2002 Model Year VCT
AWW4Gasoline51.8LMotronicInline  9.3:181.086.41781NoYes2001 Model Year VCT
                

I5 Engines

CodeCylFuel TypeValves(L)FI TypeEngine LayoutHorsepowerTorque @ RPMCompBoreStrokeCCS/CTurboNotes
AAF5Gasoline22.5LMotronicInline      NoNoT4 Eurovan
AAU5Gasoline22.2LCISInline      NoNo 
BGP5Gasoline42.5LMotronicInline150 @ 5000170 @ 37509.5:182.592.82480NoNoMkV Jetta
JT5Gasoline22.22LCISInline      NoNo 
KM5Gasoline22.2LCISInline      NoNo 
KX5Gasoline22.22LCISInline      NoNo 
WE5Gasoline22.2LCISInline      NoNo 
                

V6, V8, W8 and W12 engines

CodeCylFuel TypeValves(L)FI TypeEngine LayoutHorsepowerTorque @ RPMCompBoreStrokeCCNotes
AHA6Gasoline52.8LMotronicV190 @ 6000206 @ 320010.6:182.586.42771Passat V6
ATQ6Gasoline52.8LMotronicV190 @ 6000206 @ 320010.6:182.586.42771Passat V6
AXQ8Gasoline54.2LMotronicV310 @ 6200302 @ 300011.0:184.693.04172Touareg V8
AZZ6Gasoline43.2LMotronicV240 @ 6000229 @ 320011.3:184.096.03189Touareg V6
BAA6Gasoline43.2LMotronicV240 @ 6000229 @ 320011.3:184.096.03189Touareg V6
BAN12Gasoline46.0LMotronicW420 @ 6000406 @ 325010.8:184.090.25998Phaeton W12
BAP12Gasoline46.0LMotronicW420 @ 6000406 @ 325010.8:184.090.25998Phaeton W12
BDP8Gasoline44.0LMotronicW270 @ 6000272 @ 325010.5:184.090.23998Passat W8
BGJ8Gasoline54.2LMotronicV335 @ 6500417 @ 350011.0:184.693.04172Phaeton V8
BHX8Gasoline54.2LMotronicV310 @ 6200302 @ 300011.0:184.693.04172Touareg V8
BJH8Gasoline54.2LMotronicV335 @ 6500417 @ 350011.0:184.693.04172Phaeton 


Inlet manifold

From Wikipedia, the free encyclopedia
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In automotive engineering, an inlet manifold or intake manifold is the part of an engine that supplies the fuel/air mixture to the cylinders. The word manifold comes from the Old English wordmanigfeald (from the Anglo-Saxon manig [many] and feald [fold]) and refers to the folding together of multiple inputs and outputs.

In contrast, an exhaust manifold collects the exhaust gases from multiple cylinders into one pipe.

Carburetors used as intake runners

The primary function of the intake manifold is to evenly distribute the combustion mixture (or just air in a direct injection engine) to each intake port in the cylinder head(s). Even distribution is important to optimize the efficiency and performance of the engine. It may also serve as a mount for the carburetor, throttle body, fuel injectors and other components of the engine.

Due to the downward movement of the pistons and the restriction caused by the throttle valve, in a reciprocating spark ignition piston engine, a partialvacuum (lower than atmospheric pressure) exists in the intake manifold. This manifold vacuum can be substantial, and can be used as a source ofautomobile ancillary power to drive auxiliary systems: power assisted brakes, emission control devices, cruise controlignition advance, windshield wiperspower windows, ventilation system valves, etc.

This vacuum can also be used to draw any piston blow-by gases from the engine's crankcase. This is known as a positive crankcase ventilation system. This way the gases are burned with the fuel/air mixture.

The intake manifold has historically been manufactured from aluminum or cast iron, but use of composite plastic materials is gaining popularity (e.g. most Chrysler 4-cylinders, Ford Zetec 2.0, Duratec 2.0 and 2.3, and GM's Ecotec series).

Contents

  [hide

[edit]Turbulence

The carburetor or the fuel injectors spray fuel droplets into the air in the manifold. Due to electrostatic forces some of the fuel will form into pools along the walls of the manifold, or may converge into larger droplets in the air. Both actions are undesirable because they create inconsistencies in the air-fuel ratio. Turbulence in the intake causes forces of uneven proportions in varying vectors to be applied to the fuel, aiding in atomization. Better atomization allows for a more complete burn of all the fuel and helps reduce engine knock by enlarging the flame front. To achieve this turbulence it is a common practice to leave the surfaces of the intake and intake ports in the cylinder head rough and unpolished.

Only a certain degree of turbulence is useful in the intake. Once the fuel is sufficiently atomized additional turbulence causes unneeded pressure drops and a drop in engine performance.

[edit]Volumetric efficiency

Question book-new.svg
This section does not cite any references or sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed(July 2008)
Comparison of a stock intake manifold for a Volkswagen 1.8Tengine (top) to a custom-built one used in competition (bottom). In the custom-built manifold, the runners to the intake ports on the cylinder head are much wider and more gently tapered. This difference improves the volumetric efficiency of the engine's fuel/air intake.

The design and orientation of the intake manifold is a major factor in the volumetric efficiency of an engine. Abrupt contour changes provoke pressure drops, resulting in less air (and/or fuel) entering the combustion chamber; high-performance manifolds have smooth contours and gradual transitions between adjacent segments.

Modern intake manifolds usually employ runners, individual tubes extending to each intake port on the cylinder head which emanate from a central volume or "plenum" beneath the carburetor. The purpose of the runner is to take advantage of theHelmholtz resonance property of air. Air flows at considerable speed through the open valve. When the valve closes, the air that has not yet entered the valve still has a lot of momentum and compresses against the valve, creating a pocket of high pressure. This high-pressure air begins to equalize with lower-pressure air in the manifold. Due to the air's inertia, the equalization will tend to oscillate: At first the air in the runner will be at a lower pressure than the manifold. The air in the manifold then tries to equalize back into the runner, and the oscillation repeats. This process occurs at the speed of sound, and in most manifolds travels up and down the runner many times before the valve opens again.

The smaller the cross-sectional area of the runner, the higher the pressure changes on resonance for a given airflow. This aspect of Helmholz resonance reproduces one result of the Venturi effect. When the piston accelerates downwards, the pressure at the output of the intake runner is reduced. This low pressure pulse runs to the input end, where it is converted into an over-pressure pulse. This pulse travels back through the runner and rams air through the valve. The valve then closes.

To harness the full power of the Helmholtz resonance effect, the opening of the intake valve must be timed correctly, otherwise the pulse could have a negative effect. This poses a very difficult problem for engines, since valve timing is dynamic and based on engine speed, whereas the pulse timing is static and dependent on the length of the intake runner and the speed of sound. The traditional solution has been to tune the length of the intake runner for a specific engine speed where maximum performance is desired. However, modern technology has given rise to a number of solutions involving electronically controlled valve timing (for example Valvetronic), and dynamic intake geometry (see below).

As a result of "resonance tuning", some naturally aspirated intake systems operate at a volumetric efficiency above 100%: the air pressure in the combustion chamber before the compression stroke is greater than the atmospheric pressure. In combination with this intake manifold design feature, the exhaust manifold design, as well as the exhaust valve opening time can be so calibrated as to achieve greater evacuation of the cylinder. The exhaust manifolds achieve a vacuum in the cylinder just before the piston reaches top dead center.[citation needed] The opening inlet valve can then—at typical compression ratios—fill 10% of the cylinder before beginning downward travel.[citation needed] Instead of achieving higher pressure in the cylinder, the inlet valve can stay open after the piston reaches bottom dead center while the air still flows in.[citation needed][vague]

In some engines the intake runners are straight for minimal resistance. In most engines, however, the runners have curves...and some very convoluted to achieve desired runner length. These turns allow for a more compact manifold, with denser packaging of the whole engine, as a result. Also, these "snaked" runners are needed for some variable length/ split runner designs, and allow the size of the plenum to be reduced. In an engine with at least six cylinders the averaged intake flow is nearly constant and the plenum volume can be smaller. To avoid standing waves within the plenum it is made as compact as possible. The intake runners each use a smaller part of the plenum surface than the inlet, which supplies air to the plenum, for aerodynamic reasons. Each runner is placed to have nearly the same distance to the main inlet. Runners, whose cylinders fire close after each other, are not placed as neighbors.

"180-degree intake manifolds"....Originally designed for carburetor V8 engines, the two plane, split plenum intake manifold separates the intake pulses which the manifold experiences by 180 degrees in the firing order. This minimizes interference of one cylinder's pressure waves with those of another, giving better torque from smooth mid-range flow. Such manifolds may have been originally designed for either two- or four-barrel carburetors, but now are used with both throttle-body and multi-point fuel injection. An example of the latter is the Honda J engine which converts to a single plane manifold around 3500 rpm for greater peak flow and horsepower.

"Heat Riser"....now obsolete, earlier manifolds ...with 'wet runners' for carbureted engines...used exhaust gas diversion through the intake manifold to provide vaporizing heat. The amount of exhaust gas flow diversion was controlled by a heat riser valve in the exhaust manifold, and employed a bi-metallic spring which changed tension according to the heat in the manifold. Today's fuel-injected engines do not require such devices.

[edit]Variable length intake manifold

Lower intake manifold on a 1999 Mazda Miataengine, showing components of a variable length intake system.

Variable Length Intake Manifold (VLIM) is an internal combustion engine manifold technology. Four common implementations exist. First, two discrete intake runners with different length are employed, and a butterfly valve can close the short path. Second the intake runners can be bent around a common plenum, and a sliding valve separates them from the plenum with a variable length. Straight high-speed runners can receive plugs, which contain small long runner extensions. The plenum of a 6- or 8-cylinder engine can be parted into halves, with the even firing cylinders in one half and the odd firing cylinders in the other part. Both sub-plenums and the air intake are connected to an Y (sort of main plenum). The air oscillates between both sub-plenums, with a large pressure oscillation there, but a constant pressure at the main plenum. Each runner from a sub plenum to the main plenum can be changed in length. For V engines this can be implemented by parting a single large plenum at high engine speed by means of sliding valves into it when speed is reduced.

As the name implies, VLIM can vary the length of the intake tract in order to optimize power and torque, as well as provide better fuel efficiency.

There are two main effects of variable intake geometry:

  • Venturi effect - At low rpm, the speed of the airflow is increased by directing the air through a path with limited capacity (cross-sectional area). The larger path opens when the load increases so that a greater amount of air can enter the chamber. In dual overhead cam (DOHC) designs, the air paths are often connected to separate intake valves so the shorter path can be excluded by deactivating the intake valve itself.
  • Pressurization - A tuned intake path can have a light pressurizing effect similar to a low-pressure supercharger due to Helmholtz resonance. However, this effect occurs only over a narrow engine speed range which is directly influenced by intake length. A variable intake can create two or more pressurized "hot spots." When the intake air speed is higher, the dynamic pressure pushing the air (and/or mixture) inside the engine is increased. The dynamic pressure is proportional to the square of the inlet air speed, so by making the passage narrower or longer the speed/dynamic pressure is increased.

Many automobile manufacturers use similar technology with different names. Another common term for this technology is Variable Resonance Induction System (VRIS).

Vehicles using variable intake geometry [show]

[edit]See also

[edit]References

Wikimedia Commons has media related to: Intake manifolds
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Cylinder head

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A 302/5.0L Ford cylinder head

In an internal combustion engine, the cylinder head (often informally abbreviated to just head) sits above the cylinders on top of the cylinder block. It closes in the top of the cylinder, forming the combustion chamber. This joint is sealed by a head gasket. In most engines, the head also provides space for the passages that feed air and fuel to the cylinder, and that allow the exhaust to escape. The head can also be a place to mount the valvesspark plugs, and fuel injectors.

In a flathead or sidevalve engine, the mechanical parts of the valve train are all contained within the block, and the head is essentially a metal plate bolted to the top of the block; this simplification avoids the use of moving parts in the head and eases manufacture and repair, and accounts for the flathead engine's early success in production automobiles and continued success in small engines, such as lawnmowers. This design, however, requires the incoming air to flow through a convoluted path, which limits the ability of the engine to perform at higher revolutions per minute (rpm), leading to the adoption of the overhead valve (OHV) head design, and the subsequent overhead camshaft (OHC) design.

Contents

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[edit]Detail

Internally, the cylinder head has passages called ports or tracts for the fuel/air mixture to travel to the inlet valves from the intake manifold, for exhaust gases to travel from the exhaust valves to the exhaust manifold. In a water-cooled engine, the cylinder head also contains integral ducts and passages for the engines' coolant - usually a mixture of water and antifreeze - to facilitate the transfer of excess heat away from the head, and therefore the engine in general.

In the overhead valve (OHV) design, the cylinder head contains the poppet valves and the spark plugs, along with tracts or 'ports' for the inlet and exhaust gases. The operation of the valves is initiated by the engine's camshaft, which is sited within the cylinder block, and its moment of operation is transmitted to the valves pushrods, and then rocker arms mounted on a rocker shaft - the rocker arms and shaft also being located within the cylinder head.

In the OHC design, the cylinder head contains the valves, spark plugs and inlet/exhaust tracts just like the OHV engine, but the camshaft is now also contained within the cylinder head. The camshaft may be seated centrally between each offset row of inlet and exhaust valves, and still also utilizing rocker arms (but without any pushrods), or the camshaft may be seated directly above the valves eliminating the rocker arms and utilizing 'bucket' tapets.

[edit]Implementation

The number of cylinder heads in an engine is a function of the engine configuration. Almost all inline (straight) engines today use a single cylinder head that serves all the cylinders. A V (or Vee)engine has two cylinder heads, one for each cylinder bank of the 'V'. For a few compact 'narrow angle' V engines, such as the Volkswagen VR6, the angle between the cylinder banks is so narrow that it uses a single head spanning the two banks. A flat engine (basically a V engine, where the angle between the cylinder banks is now 180°) has two heads. Most radial engines have one head for each cylinder, although this is usually of the monobloc form wherein the head is made as an integral part of the cylinder. This is also common for motorcycles, and such head/cylinder components are referred-to as barrels.

Some engines, particularly medium- and large-capacity diesel engines built for industrial, marine, power generation, and heavy traction purposes (large truckslocomotivesheavy equipment etc.) have individual cylinder heads for each cylinder. This reduces repair costs as a single failed head on a single cylinder can be changed instead of a larger, much more expensive unit fitting all the cylinders. Such a design also allows engine manufacturers to easily produce a 'family' of engines of different layouts and/or cylinder numbers without requiring new cylinder head designs.

The design of the cylinder head is key to the performance and efficiency of the internal combustion engine, as the shape of the combustion chamber, inlet passages and ports (and to a lesser extent the exhaust) determines a major portion of the volumetric efficiency and compression ratio of the engine.

Automotive 4-Stroke Engine Head Designs - Valve and Camshaft Configurations

Common NamesCamshaftIntake ValvesExhaust ValvesNotes
Dual Overhead Cam
DOHC
HeadHeadHeadAllows optimum positioning of the valves for a crossflow cylinder head.
Double camshafts are used to allow direct actuation of well-placed valves, without rockers.
Widespread in modern car design
Overhead Cam
OHC
HeadHeadHeadWidely used for cars in recent decades, but increasingly superseded by DOHC.
Overhead Valve
OHV, I-Head, Pushrod
BlockHeadHeadStill used in big V8 pushrod engines
Needs pushrods and rockers to actuate valves
Sidevalve
Flathead, L-Head, T-Head
BlockBlockBlockOnce universal, now obsolete
Simplest possible configuration
Cams operate directly on the valves
Inlet-Over-Exhaust
IOE, F-Head
BlockHeadBlockAlways rare, obsolete in cars
Common in motorcycles, especially Harley-Davidsons

[edit]Gallery

  • A cylinder head sliced in half showing the intake and exhaust valves, intake and exhaust ports, coolant passages, cams, tappets and valve springs.

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  • single overhead camshaft(SOHC) cylinder head from a Honda D15A3.

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  • double overhead camshaft(DOHC) cylinder head from a Honda K20Z3.

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  • The bottom (left) and top (right) of a Malossi cylinder head for single-cylinder, two-stroke scooters. Hole in the middle for the spark plug, four holes for the cylinder bolt posts.

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  • Overhead view of an air-cooled cylinder head from aSuzuki GS550 showing dual camshafts, drive sprockets and cooling fins.

  •  
  • The cylinder head from aGMC van. The valves and part of the exhaust 


    manifoldare visible.

[edit]See also

INTAKE MANIFOLDS

A Guide to Intake Manifolds for Carburetors

There are countless options for choosing an intake manifold. Some intakes will help you make power down low, while others will help with top end power. Choosing the right intake is a matter of your application and the kind of horsepower your engine will potentially make. We'll give you Intake Manifold basics and then get more technical at the end.

Intake Manifold Format

You've heard the terms: High rise manifold, dual plane, single plane, tunnel ram....Each manifold type has a purpose in the performance world.

Dual Plane Intake Manifolds

Dual plane intake manifolds are named for their split plenum opening in the intake where the carb sits. Each side of the opening feeds 4 cylinders on a V8. Dual plane intake manifolds are the most popular for high performance street and mild racing because they generally build power across a wider range and start at 1,500 RPM, depending on the dual plane manifold. Each intake manifold has its own performance characteristics. It's best to know how you'll use your vehicle and select from there. To be clear: Dual plane has nothing to do with the number of carburetors that the intake will accept. You can have a dual plane manifold that accepts 1 or 2 carburetors.

Single Plane Intakes

Single plane manifolds are named for their intake opening where the carb is bolted on. A single plane intake has one "hole", in the plenum where the carburetor sits on the intake. Fuel from the carburetor enters the intake through one opening with no separation. That single hole feeds all 8 cylinders on a V8. They are typically less restrictive and work best to build power between 3,000 and 8,000 RPM's. Because of the RPM range, the single plane intake manifold is best suited for racing applications.

Square Bore Intakes

Carburetors have venturis that open and close as you apply the throttle. A 4 barrel square bore carb has 4 equal sized venturis that you can more easily see from the underside ofthe carb. Square bore intake manifolds match the square bore shape of the carburetor base and venturis.

Spread Bore Intakes

Spread bore carburetors have 2 small venturis up front that are the primaries and 2 larger secondaries on the rear of the carb. Spread bore intake manifolds match that shape to accomodate the larger venturis toward the back.

Low Rise Intakes

Low Rise refers to the height of the intake. Low rise is a general term used to describe intake manifolds. There is no clear distinction between a low rise and a medium rise intake. It's pretty easy to describe an intake manifold as low or high rise. Low riseintakes fit under hoods better and offer certain performance advantages over taller intakes.

High Rise Intakes

High rise intakes are taller than low rise. High rise is a general term to describe an intake. There is no standard height where low rise intakes end and high rise intakes begin. High rise intakes are better at building horsepower in the upper RPM range and usually have a wider power band.

Tunnel Rams

Tunnel ram intakes are extreme Hi Rise intakes that accomodate one or two 4 barrel carburetors. They are made for high RPM and big horsepower setups. You see tunnel rams on the street, but they are best suited at the track where you can really get into the higher RPM's.

So, How do I select the right manifold for my application?

As with many situations in building an engine, it should match your intended purpose. Everyone wants the big tunnel ram dual quad intake sticking out of the hood, but it may not be practical, or best, for maximum performance. All intakes advertise an RPM range that identifies where they are most efficient. As an example, the intake may advertise "1,500-6,500 RPM". This RPM range must be considered and is the easiest guide to choosing the right intake for you. Street cars work best with a dual plane intake, most advertised "idle to 6,000 RPM" or "1500-6500 RPM". Race cars that work more in the upper RPM ranges will require a single plane, ?2,500-7,000 RPM? or "3,500-8,000 RPM". Next, the intake and camshaft selection should go hand in hand. The camshaft will also state an RPM range for its best performance. The RPM range of the camshaft and intake should match or be very close. A minimal low RPM difference of 500 RPM is acceptable, but should not exceed 1000 RPM. If this is the case in your selections it is better for the intake RPM range to start lower than the camshaft. The reverse may cause low end instability, thus an off throttle hesitation. Lastly you need to consider the physical fitment. Most obviously, be sure to select the appropriate part number for the engine and cylinder head design. Consideration for engine vacuum ports, water coolant ports, carburetor flange fitment, and be sure to check for proper hood clearance.

For all of you automatic transmission hot rodders out there, be sure to see our tech section ontorque converters too. Once you?ve selected your intake manifold and camshaft, be sure you have the right torque converter too!

AN fuel fittings and braided hoseFuel pressure regulatorsFuel Filters

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