Installation & Operation Manual
O-360 and IO-360 Series Engines
9 Chapter 3 • Aircraft / Engine
© March 2004 Superior Air Parts Inc. Integration Considerations
5. EXHAUST SYSTEM
The engine exhaust system’s primary role is to
transfer engine exhaust gasses from the cylinder
heads overboard in a safe and efficient manner.
Exhaust systems serve to reduce engine noise,
provide heat sources for carburetor and cabin
heaters and even act to enhance engine
performance in terms of both power and fuel
efficiency. Improperly designed exhaust systems
can create health risks to aircraft occupants and
can be detrimental to engine performance.
A. Health and Safety Issues
Carbon monoxide is a colorless, odorless gas
that is potentially lethal and a basic by-product
of internal combustion engines. The primary
role of exhaust systems to safely conduct this
gas from the combustion chamber away from
persons on-board the aircraft cannot be
overstated. Exhaust systems must be airtight
with no potential for carbon monoxide leaks and
must exit outside the aircraft in a location where
gases will not be reintroduced to the airframe.
Due to the extreme temperature of exhaust
system components (up to 1600
°
F), care must
also be taken to isolate combustible materials.
This includes flammable liquids such as fuel, oil
and hydraulic fluid as well as dry combustible
materials.
B. Exhaust System Design and Sizing
Several styles of exhaust systems are
commonly used in piston aircraft engines.
Engines with smaller power ratings sometimes
use “stub” or “direct” exhaust systems. These
systems simply provide a short section of
exhaust pipe to direct the exhaust gas away
from the cylinder head and are not connected
with each other. While these systems are
typically the loudest and least beneficial in terms
of performance enhancement, they can hold the
benefit of being the lightest design. Although it
is possible to use this type of system on
Superior Vantage Engines it is not the
recommended approach.
Another exhaust design style is to connect 2 or 4
of the exhaust tubes together before exiting the
aircraft. Commonly referred to as 2-into-1 or 4-
into-1 systems, these designs feature a space-
efficient way to transport the exhaust gas safely
overboard. Although these systems are not
designed to add substantial performance
benefits to the engine, they can rob power and
efficiency if not properly designed. The
intersections of the exhaust pipe segments must
be designed such that pressure pulsations
traveling down a given exhaust pipe do not
adversely effect the operation of cylinders with
intersecting pipes. If pressure pulsations
traveled from one exhaust pipe and back “up”
another, excessive pressure could be present as
the second cylinder’s exhaust valve opened and
cause a disruption to the exhaust gas exit. High
back pressure, whether caused from basic
system flow restrictions or pressure waves of
adjacent cylinders can have significant effects
on volumetric efficiency and thereby on power
output and fuel efficiency.
A third exhaust system style is commonly
referred to as a crossover design. This style
connects the exhaust pipes of two cylinders in
such a manner as to enhance performance. In
an ideal crossover system, as the pressure
wave from one cylinder passes the connection
point of the two exhaust pipes a slight suction is
created in the exhaust pipe of the second
cylinder. When properly tuned, this suction is
caused as the exhaust valve of the second
cylinder opens and aids in the emptying of the
second cylinder. The pressure wave of the
second cylinder then creates a slight suction in
the exhaust pipe of the first cylinder, aiding in its
emptying. This behavior improves the breathing
of the cylinders and can have volumetric
efficiency, power and fuel efficiency benefits.
For Superior Vantage Engines with 4 cylinders,
crossover exhaust systems should couple
cylinder 1 with cylinder 2 and cylinder 3 with
cylinder 4. Crossover exhaust systems are
typically less space efficient and a little heavier
than other styles, but have the unique benefit of
enhancing performance of the engine.
Regardless of the style employed, several
factors should be considered to make an
effective exhaust system.