Manifold Tuning

1
Manifold Tuning

• Erik Fernandez
• Michelle Hood
• Sladana Lazic

2
Overview

• What are the intake and exhaust manifolds
• What is manifold tuning
• Theory of manifold tuning
• Helmholtz Resonator
• Compression-expansion waves
• Other tuning considerations
• Flow friction through manifold
• Charge Heating

3
What is a Manifold?

• Intake Manifold
• A set of passages or pipes used to conduct air or
  a fuel/air mixture to the cylinders.

4
Intake Manifold Types

5
What is a Manifold?

• Exhaust Manifold
• A set of passages or pipes which conduct exhaust
  gases from the engine.

6
Exhaust Manifold Types
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Manifold Tuning

• What is it?
• Tuning is the optimization of the manifold
  configuration
• Why is it important?
• Engine breathing is enhanced if the intake
  manifold is configured to optimize the pressure
  pulses in the intake system
• The more air-fuel mixture an engine burns the
  more power it produces
• Volumetric efficiency is also increased

8
Manifold Tuning

• What is Volumetric Efficiency?
• The efficiency with which the engine can move the
  charge into and out of the cylinders
• It is a ratio of what volume of fuel and air
  actually enters the cylinder during induction to
  the actual capacity of the cylinder
• What is engine breathing?
• An engine's ability to fill its cylinders with
  air-fuel mixture and then discharge the burnt
  exhaust gases

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Helmholtz Resonator
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Helmholz Resonator

• A Helmholtz resonator is a simple harmonic
  oscillator where the mass is provided by the air
  in a narrow neck while the spring is provided by
  a volume of trapped air.
• When modeled as a second order differential
  spring-mass system the natural frequency of the
  Helmholtz resonator is.

a velocity of sound A area of the valve V
volume of the trapped air L length of the pipe
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Helmholz Resonator (Complications)

• Most of the time the valve is not fully open,
  therefore we model it as an orifice with area
  A1.
• After applying the Bernoulli equation, Newtons
  Second Law, and linearize it we get a more
  realistic result for frequency

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Helmholtz Resonator (a four cylinder engine)

• The branches of the inlet manifold that lead to
  the three closed valves are modeled as the
  Helmholtz resonator.
• Modeled with two pipes L1 and L2, and a volume V
  that is equal to the volume of the three manifold
  branches that are leading to the closed valves

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Organ Pipes-compression expansion waves
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Organ Pipes

• Mass in pipes is compressible
• Two types of wave
• Compression Wave
• Corresponds to an increase in pressure
• Expansion Wave
• Corresponds to a decrease in pressure

15
Organ Pipes continued

• Incident waves can be transmitted or reflected
• Transmission
• Transmitted wave is of the same type as the
  incident wave
• Reflection
• If incident wave sees a larger cross section,
  reflected wave is of the other type
• If incident wave sees a small cross section,
  reflected wave is of the same type

16
Organ Pipes continued

• After the valve opens, pressure in the cylinder
  drops sending an expansion wave up the pipe

• Expansion wave is reflected as a compression wave

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How to Optimize Runner Length
Where ? is the ratio of valve open angle to
pi a is the Isentropic Speed of sound V is the
fluid velocity N is the number of revolutions
per second
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How to Optimize Runner Length

• With a fixed fluid velocity the trend can be
  observed
• Higher Engine speeds Require shorter runners
• Lower Engine Speeds require longer runners

Graph of Intake Runner Length vs. Engine RPM
using the previous equation.
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Implications for Manifold Tuning

• Can only tune for a very narrow rpm range
• The tuning effect will decrease on either side of
  selected rpm speed.

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Practical Applications

• Engine Compartment space limits intake runner
  length
• Possible Solutions
• Manifold Folding
• Separate tuned runners
• Reduce runner length by factor

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Manifold Folding

• Manifold can be folded to achieve optimum low
  speed rpm length
• A valve can switch between the two paths the
  waves take

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Manifold Folding cont.

• Example of folded manifold with two way valve
• This setup can be done for each intake runner or
  the air intake itself to serve all the cylinders

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Separate Tuned Runners

• Each cylinder has two intake runners
• Have a long runner for low rpm and a short runner
  for high rpm
• Valve actuators switch between the two runners

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Separate Tuned Runners cont.
Low RPM Runner
Throttle Body
High RPM Runner
Vacuum Actuated Valve
Intake Plenum
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Reducing Runner Length by factors

• If a runner length is too large its total length
  can be reduced by a factor.
• A 20 inch long runner can be reduced by a factor
  of 4 and a 5 inch runner will be equivalent.

Intake Velocity Stacks
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Exhaust System Tuning

• Exhaust Manifold tuning is similar to intake
  manifold tuning
• The same wave theory can be used to optimize
  header length
• Compression wave is emitted and the expansion
  wave returns to clear the exhaust gases

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Exhaust System Tuning cont.

• Exhaust temperature greatly affects header length
• Higher Temperature increases speed of sound

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Exhaust System Tuning cont

• Header Length as a function of gas temperature

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Implications For Exhaust Manifold Tuning

• Because of the higher temperatures Longer headers
  must be used.

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Additional Exhaust Tuning Considerations

• Gas exit speed
• High velocity gas indicates restriction
• Low velocity gas makes power curve peaky and
  hurts low end power
• Header pipe diameter
• Larger diameter tubes allow gases to expand,
  thus slowing down gas speed and wave speed

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Additional Exhaust Tuning Considerations

• Collector package
• Number of pipes per collector
• Outlet sizing
• Collector shape

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Header Configurations

• 4-2-1 Configuration
• 4-1 Configuration
• Allows pulses to interact in a way that makes
  more torque

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Exhaust Collectors

• Collectors merge all of the primary pipes
  together
• Dead space in the middle should be eliminated to
  reduce turbulence

More efficient merge of primaries
Simplest way of joining primaries together
Merge collector is one of the best ways for
joining primaries, primaries joined smoothly to
avoid turbulence
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Exhaust Collector Length

• The longer the collector, the higher up the power
  band is shifted
• Need enough length to smoothly join gases from
  primaries to avoid turbulence

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Other Tuning Considerations

• Flow Friction through Manifold
• Charge heating

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Flow Friction Through Manifold

• Although not as crucial as the unsteady
  compressible flow dynamics, flow friction plays a
  role in manifold tuning
• By lowering the surface roughness the air flow
  becomes smoother

37
Flow Friction Through Manifold cont.

• Porting and polishing is one of the best ways for
  aftermarket engine improving
• Once engines are modified, more intake manifold
  is needed to make more power

Ported Intake passages from Subaru WRX
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Intake Charge Heating

• As the intake charge gets colder the mass going
  into the engine increases due to increased
  density
• Primary Sources of Intake Charge Heating
• Hot inducted air from engine compartment
• Heat transfer from manifold to intake charge
• Heat transfer from intake valve to intake charge
• (only for force inducted engines) turbocharger
  or supercharger
• A very important issue on Force Inducted engines
• Intake charge can reach extreme temperatures
• Extreme intake temperatures can lead to
  detonation

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Intake Charge Heating Solutions

• Cold air induction
• Intake manifold and cylinder head thermal coating
• Intercooler (force inducted engines only)
• Nitrous oxide injection
• Alcohol/water injection

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Intake Charge Heating Solutions cont.
Cold air intake
Intercooling
Alcohol/Water injection
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Summary and Conclusion

• Manifolds are passages that conduct air/fuel
  mixtures
• Intake manifolds conduct air/fuel into the
  cylinder
• Exhaust manifolds conduct waste combustion
  products out of the cylinder
• The main goal of manifold tuning is to increase
  the volumetric efficiency
• Manifold tuning involves not only fluid mechanics
  but also thermodynamics
• Intake and exhaust manifolds must be designed to
  complement each other
• Several factors within the intake and exhaust
  system contribute to loss of volumetric
  efficiency

42
Questions?