Replacing
your vintage vehicle exhaust system
When your vintage vehicle needs a new exhaust system
or components, you are faced with a wide variety of
options and decisions about the parts you will install.
Here are some of the critical things you need to know
and consider before spending your hard-earned dollars
on that next exhaust system.
We are focused here on typical Four-stroke Internal
Combustion (IC) engine systems for vehicles built from
the earliest days of the horseless carriage up to the
introduction of catalyzed systems in the mid-1970s.
Newer vehicles utilize the same basic components, but
also employ catalytic converters (2 or 3-way), a variety
of thermal and oxygen sensing components and active
control technologies to meet emissions standards.
Let’s start with the basic elements of exhaust
systems. Most single systems consist of an exhaust manifold,
exhaust pipe, silencer (muffler and/or resonator) and
tailpipe. Dual systems typically use two exhaust pipes
or an H pipe, two to six mufflers/resonators and two
tailpipes. We’ll start with a brief review of
your material choices and then cover each of the major
components in turn.
Material Choices
When you replace exhaust components, you can choose
from a variety of materials. The OEM parts installed
on your new vehicle were typically manufactured in low-carbon
steel. Beginning in the late 1930’s, mufflers
were often made using galvanized steel for improved
corrosion resistance. Aluminized steel and stainless
steel were introduced into mainstream production vehicle
exhaust components in the late 1970’s. Most OEM
manufacturers introduced stainless steel components
after 1975 with the advent of catalytic converters.
Today, you will find components manufactured from these
materials:
- Low-carbon steel (poor corrosion resistance, but “correct”
and original for most vehicles). Most “Old Stock”
parts are low-carbon, “regular” steel or
galvanized parts.
- Aluminized steel (very good corrosion resistance and
durability; performs and looks good for many years with
typical vintage vehicle usage and care)
- Stainless steel (excellent appearance and durability.
“300” Series stainless is more brittle and
has poorer thermal shock performance than “409”
Series stainless, which is most often used in today’s
OEM stainless systems)
Cast iron exhaust manifolds or tubular exhaust
headers
Typical original equipment (OEM) production manifolds
are manufactured from cast iron (inexpensive, durable
and tolerant of high-temperature gases). These manifolds
are “optimized” to balance production costs,
manufacturing simplicity, ease of assembly, durability
and performance. They direct the hot exhaust gases away
from the cylinder head/exhaust port and into the primary
exhaust pipe. They are not generally capable of optimal
flow, but they are quiet, durable and strong. In many
cases, they incorporate a heat riser valve or pre-heater
to aid in cold engine warm-up, emissions control and
drivability.
Many high-performance applications in the 1960’s
and 1970’s utilized long-tube manifold designs
to improve output and engine breathing. The Pontiac
HO/Ram Air manifolds, the MOPAR Max Wedge, Hi-Po &
Hemi manifolds and the Ford Hi-Po manifolds are all
examples of these higher-flow manifolds. These designs
improved exhaust gas flow over standard manifolds by
utilizing a design that more closely resembles a tuned-length
header. Though not as free-flowing or effective at scavenging
exhaust gas as tuned headers, these manifolds represented
a superior alternative to the basic “log”
that most production manifolds resemble.
Performance part suppliers jumped into the performance
improvement aftermarket with tubular headers for nearly
every engine and vehicle combination. By matching the
length of the header tubes, the exhaust pulses from
each cylinder can be tuned to reach the exhaust pipes
in an orderly fashion. Well-designed manifolds or headers
can actually improve the scavenging of spent exhaust
gases from the cylinders by using the pulse from previous
cylinder output to “pull” the gases from
the next cylinder – almost as if the exhaust pulse
is being vacuumed out of the cylinder by the previous
pulse. A good set of headers can improve torque and
horsepower by more than 10% compared to standard factory
exhaust manifolds.
If you are using production, cast iron manifolds in
your vehicle, follow these steps to help ensure a quiet,
trouble-free installation. Make sure that the sealing
surfaces are flat and that the heat riser valve (if
originally present) is properly installed and operating
freely. Treat the manifolds with a high-quality cast
iron coating after media blasting them. Use bolt locks
where they were originally installed and a high-quality
gasket. Follow the bolt installation sequence that is
specified in your service manual and tighten the attachments
to the specified torque in the proper sequence. (Usually
starting at the center and working alternately forward
and rearward) This maintains the flat sealing interface
between the manifold and the head and minimizes the
potential for leaks and cracks.
Exhaust pipes
Once the gases exit the manifold/header, they are conveyed
rearward under the vehicle by the exhaust pipes. Production
pipes were designed to optimize gas flow while maintaining
underbody and ground clearances. They were normally
press-bent or “push-bent”, with a slight
deformation of the circular cross-section of the tube
in areas of significant bends. They often include flattened
sections for clearance to frame cross members, transmission
mounts or other chassis and suspension parts.
Replacing your exhaust pipes with larger diameter pipes
can help performance, but it can also cause significant
clearance and interference problems. If you are considering
a larger diameter system, save yourself a lot of frustration
and aggravation by verifying that there is sufficient
clearance for the pipes you are considering. Don’t
just inspect the system statically; get a helper to
move the tailpipe outlets to the limits of the hanger
isolator motion and rock the vehicle to full suspension
travel if possible. What looks like sufficient clearance
can become interference when the engine moves under
hard acceleration or when the suspension moves to the
limits of its travel.
H pipes, X pipes and competing claims
There are many suppliers of performance exhaust systems
making claims of huge torque and horsepower gains to
be had by utilizing their X or H pipe designs. Do your
homework; evaluate the claims in light of your intended
use of the vehicle and be certain that the claims are
substantiated by hard data, preferably comparisons of
vehicle performance with ONLY that specific exhaust
system change having been made between comparative measurements.
Dynamometer data is useful, but be certain that you
understand what was done to the engine/vehicle to achieve
the published results. Most of us won’t be operating
our vintage vehicle for extended periods under racing
conditions, so consider how important the results are
for your vehicle driving patterns!
There ARE inherent benefits to improving the breath-ability
of your exhaust system. Engines are basically big air
pumps. The less restriction there is to exhaust flow,
the better the engine can process incoming fuel/air
mixtures and the more power the engine will produce.
H Pipes provide a balance of the exhaust gas pulses
between the two exhaust pipes, equalizing the system
pressure in the two “sides” of the exhaust
system. This generally provides improved low-end torque
and some amount of top-end horsepower improvement. An
“X” pipe design may provide a slightly better
result than a simple H pipe on identical applications,
especially at higher engine speeds. Whichever way you
go, be certain to re-tune your engine for the changes
you’ve made in the exhaust system. A reduction
in exhaust system back pressure can allow improved breathing,
which will probably require carburetor re-jetting, idle
mixture and idle speed adjustments, ignition timing
adjustment and spark plug changes.
Many high-performance vehicles manufactured after 1960
were available with factory-installed duals that incorporated
H pipes. In many cases, your car can be equipped with
an OEM style H pipe and duals, even if it was originally
equipped with a single exhaust system. The factory dual
system can be a great performance and sound improvement.
Silencers (Mufflers and Resonators)
Exhaust noise silencers come in a variety of shapes,
sizes and designs. They are generally grouped into two
major types; resonators and mufflers. Let’s look
at both of them.
Mufflers
Mufflers are designed to reduce the pulsation and volume
of the outbound exhaust pulses. This is generally accomplished
by a series of perforated tubes installed in a sealed
chamber (or “case”) that force the exhaust
gases through a series of loops or turns while allowing
the gases to cool. The tube diameters, perforations
and flow patterns are designed to reduce the sound levels
and pulsations while providing the desired tone and
sound levels both outside and inside the vehicle. Two-tube,
three-tube, chambered and straight-through designs are
the most common.
In a two-tube design, the exhaust gases enter the muffler
through the inlet tube and are forced to “find
their way” to the outlet tube by passing through
the perforations or holes in the inlet tube and the
sound-absorbing materials or chambers that surround
the inlet tube.
In a three-tube muffler, the exhaust gases follow a
“double reverse” flow pattern, transferring
from the inlet tube into an intermediate tube and then
finally into the outlet tube. Three-tube designs are
generally quieter than two-tube designs.
In a chambered design, the inlet tube is short and dumps
into an expansion chamber. Exhaust gases have less restricted
flow paths to enter the outlet tube.
Straight-thru, single tube designs generally are the
loudest and lowest restriction mufflers. The inlet and
outlet tube are one piece, with a series of holes or
perforations that allow the gas pulses to expand into
the muffler case area, which is usually filled with
a glass fiber or similar material to provide some quieting.
Muffler design is a complex science. Most mufflers are
designed to fit a wide range of vehicle/engine applications
and you will usually find many options for your specific
vehicle. You will probably be happy with any of the
products that are offered by the major exhaust component
manufacturers to fit your application, but if you have
very specific sound and performance requirements, research
can save you headaches and unnecessary cost. Read up
on any test data that compares the brands and models
of mufflers that you are considering. Check websites/forums/tech
advice/car club Resources – chances are very good
that someone with your same desires has already found
a combination that works great for your vehicle! Beware
of extremely loud performance mufflers that sound very
aggressive; some of these very loud mufflers actually
flow no better than quieter, high-flow designs. In addition,
many vehicle owners do not like the interior sound levels
and the resonance these loud mufflers can create.
Resonators
Resonators are utilized on a wide variety of passenger
car and truck exhaust systems. They typically utilize
a “straight-through” case or tube that attenuates
and tunes the sound of the exhaust pulses. Resonators
are most often installed just before exit point of the
exhaust system, but in some applications the resonator
is installed in front of the muffler. Some resonators
are designed as simple, hollow expansion or sound chambers
with no sound absorbing materials. These are acoustically
tuned to deliver the desired exhaust note. They primarily
use reflective wave cancellation techniques to eliminate
the undesired frequencies while allowing desired frequencies
to pass unabated.
Most exhaust system providers will provide replacement
exhaust systems with or without the resonator component.
A straight pipe replacement can be installed if the
resonator is not desired. Without the resonator, your
exhaust system will usually sound slightly louder and
less mellow, with a sharper and “raspier”
exhaust note evident under hard acceleration.
Tailpipes
Tailpipes guide the spent exhaust gases to the rear
of the vehicle. In the earliest vehicles, they were
often no more than a short “turn-down” at
the rear of the muffler case, exiting under the vehicle.
Over the years, the desire to convey noxious exhaust
fumes away from the vehicle occupants drove the exit
points to the rear of the vehicles. In many truck and
station wagon vehicles, the tailpipe exit point is just
rearward of the rear wheel opening. This keeps exhaust
gases from being drawn back into the low pressure area
at the rear of a station wagon. Interestingly, many
high performance vehicles of the 50’s, 60’s
and 70’s employed the shorter tailpipe designs
of the station wagons with side exits behind the rear
wheels. Are you restoring a 396 Chevelle or Impala from
1965-68 or a 1970 Torino GT? Make certain you are getting
the correct tailpipe design for your vehicle!
Tuning AFTER you make exhaust system changes
We can’t over-emphasize the need to tune for
optimal performance after making significant exhaust
system changes. If you merely replace an OEM-style muffler
with a new direct replacement, you needn’t worry
about tuning. But if you have removed a factory single
exhaust and replaced it with an OEM style H pipe and
dual exhausts with low-restriction mufflers, you owe
it to yourself and your engine’s long term health
to re-tune your engine to take full advantage of the
new exhaust systems’ capabilities!
Summing it up
Your exhaust system plays a critical role in the overall
performance, sound and driving comfort of your vehicle.
Choosing the correct combination of components and materials
will give you the performance and sound that you expect.
When it’s time to replace your system, investigate
and understand the options available to you; you’ll
be glad you did!
© J Tonietto Waldron's
Antique Exhaust Inc -
All Rights Reserved
Call Us Today 269-467-7185 or (US) 800-503-9428 for your exhaust system needs
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