Internal Combustion
Engine
Induction Tuning



ME 468 Engine Design 

Professor Richard Hathaway 

Department of Mechanical and
Aeronautical Engineering 
Port Sizing
Considerations
Swept and Displaced
Volumes
Port Sizing and Mach
Index (Z)



Mach Index is the ratio of the velocity
of the gases flow area to the speed of sound 
Port Sizing and Mach
Index (Z)



For instantaneous relationships: 
Port Sizing and Mach
Index (Z)




Speed of Sound: 

Temperature and F/A ratio dependant 

At Standard Temperature and Pressure 


Port Sizing and Mach
Index (Z)




Modern performance engines will use
multiple inlet and exhaust valves per cylinder. 

Many are using multiple intake runners
per cylinder to improve cylinder filling over a broader range of RPM. 

A single runner is used at lower RPM
while a second runner will be opened at higher RPM. 

The second and the combined each have
their own tuning peak. 
Inlet Air Density and
Performance
Inlet air density



Law of Partial Pressures: 





If each is considered as a perfect gas 


Inlet air density



Inlet Pressures and Densities: 
Inlet air density



Inlet Pressures and Densities: 











From Ideal Gas Law 
Inlet air density
Inlet air density




Example Problem: 

Find the change in indicated power when
changing from Gasoline to Natural Gas fuels 

Assume: P_{i} = 14.0 psia T_{i} =
100oF 

j = 1.2 => 20 % Rich 

h = 0.02 lb_{m}/lb_{m
air} 
Inlet air density



Gasoline: 







Natural gas: 

F/A = 1.2 x 1/17.2 = 0.0697 lb_{fuel}/lb_{air} 

Fuel is a gaseous fuel and is
100% vaporized 
Inlet air density
Inlet air density



NATURAL GAS: 









INDICATED POWER RATIO: 


Inlet air density
Inlet air density
ACOUSTIC MODELING
Induction System
Comparisons
Acoustic Modeling
Acoustic Modeling
Acoustic Modeling
Build Considerations
Acoustic Modeling
Multiple Stack with
pressure box
Acoustic Modeling



For a single degree of freedom system 
Individual Throttle Body
with Plenum
Helmholtz Tuning



Writing Clearance Volume in Terms of
Compression Ratio: 







The Primary Volume is considered to be
the Cylinder Volume with the Piston at midstroke (effective volume). 
Helmholtz Tuning



The tuning peak will occur when the
natural Helmholtz resonance of the cylinder and runner is about twice the
piston frequency. 
Helmholtz Tuning



The EFFECTIVE INDUCTANCE for a pipe
with different crosssections may be defined as the sum of inductances of
each section. 
Helmholtz Tuning



INDUCTANCE RATIO (a) 









The CAPACITANCE RATIO (b) is defined as
the ratio of the Secondary Volume to the Primary Volume. 
Helmholtz Tuning



Calculate the Separate Inductances: 











Determine the Inductance Ratio (a) 
Helmholtz Tuning



Determine the Capacitance Ratio (b) 







Determine the Induction system
Resonances 
Helmholtz Tuning



Determine the Primary Resonance: 





Determine the Frequency Ratios: 





Determine the Tuning Peak: 
Helmholtz Tuning



Intake Tuning Peaks become: 
Helmholtz Tuning



A combined equation is possible
indicating it’s 2^{nd} order 
David Vizard’s “Rule of
thumb” Equations
The End