 The
Story Behind Car Chemistry
The Sound Of Performance
Maybe we should say “ the lack of sound”. With all Major
Sanctioning organizations requiring a reduction in sound
levels, the track will be getting quieter. The upside to
this is that the effort put into developing muffling
systems that meet the requirements without significantly
effecting performance means that not only will race
tracks be able to stay open but the street performance
market will benefit as well.
For many years it was known that stock and stock
replacement mufflers restricted performance. While many
designs were put forward to address the restriction
created by mufflers, it is only recently that truly
effective systems have been developed. Lets look at the
problems and a new and unique solution.
As we know an engine is a large air pump. This air,
after being used to drive the piston down must exit the
engine. The sound of combustion, the temperature of the
exhaust and the velocity of the air combine to create
“noise”. Traditionally the way to reduce the volume of
sound was to create back pressure. The net result was a
quieter engine with reduced power. When the need to
reduce sound to an acceptable level without loosing
significant power became an issue, various means were
explored to accomplish this.
Within the muffler case internal flow paths were
developed that used the energy of the sound pulse to
cancel certain higher frequency sounds. Large chambers
were utilized to create low pressure sound absorbing
areas within the muffler. By increasing the muffler size
as well as the inlet and outlet sizes, to allow bigger
diameter exhaust pipes to be used, back pressure was
reduced. In other instances plates were used to
interrupt the flow of exhaust, “baffling”, the exhaust
pulse. By slowing the flow down, the exhaust was allowed
to cool, reducing the higher frequency, sharper notes.
Certain “straight through” designs were developed that
used sound absorbing materials or packing to reduce
sound levels. Of course some designs utilized more than
one feature to accomplish their goal. In all instances
there was a trade off in benefits. Smaller more compact
units required the flow path to be radically altered
thus increasing back pressure, particularly at high
RPM’s. Packing increased the weight and was subject to
deterioration and water absorption. Turbulence was also
created by these designs that created back pressure even
though to the eye you were seeing what appeared to be a
straight through exhaust path. While some mufflers
allowed “tuning” the swap was still sound, for back
pressure. The most effective generally were the larger
case type mufflers. The flow path could be made large
enough that the “routing” of the exhaust gasses through
the sound attenuation areas could be accomplished
without excessive back pressure. Of course these designs
weigh a great deal and take up significant room.
At this point the market was in good shape. Then the
rules were instituted and it all changed.
Lets look at one of the rules. Sound levels cannot
exceed a Dba of 95 measured at a point 50 feet from the
outlet and with the engine turning 3500 RPM’s. Doesn’t
sound too bad, as this is way above the typical street
requirements of many States and municipalities.
The very low restrictive mufflers that were used where a
“muffler” was required, but no real sound level
requirements were required, didn’t always work. They
were so inefficient from a sound perspective that they
couldn’t meet the tighter requirements. They “looked”
like a muffler, but they didn’t really reduce the sound
levels significantly. Those that could be “tuned” to
meet the requirements caused a loss in power. This
became so serious that at least one track was closed by
the city when cars on the track were found to be in
non-compliance with the requirements. The racers and
audience were told to go home and the track was told to
shut down the race. At another facility the
non-compliant racers were told to put their cars on
trailers and leave the track. They could not even stay
and watch the racing.
Now it is recognized that some sacrifice in power would
be initially necessary. However in most cases you can
tune the power level back. Remember that when you change
from a restrictive exhaust to a free flowing design it
may be necessary to “richen” the engine slightly. This
is very common when changing from stock exhaust
manifolds to headers. When you create more back pressure
than desired a slight leaning out will gain back all or
most of the lost power. This of course assumes that your
system, including headers, collector size, exhaust pipe
size will allow the muffler to work properly. This was
recognized years back and explains why so many
competition systems run 3” diameter and larger pipe
sizes with performance mufflers. This of course is
oversize for most street systems.
Into the game enters a new product.
CC INSERTS.
These
muffler replacements
make use of a design so unique that is a
patented design. First of all the design is a “straight
through” design. Thus not creating back pressure by
placing baffles or pulse diverters in the path of air
flow. No packing is used. The
Insert
requires no case, saving weight. It is so effective that
an
Insert
weighing no more than ¾’s of a pound will allow
virtually any engine to meet the sound requirements,
with minimal to no power loss. In fact low and midrange
power generally increases. Where top end power is lost
it can be compensated for with the normal tuning change
typically needed with a slight increase in back
pressure. Since scavenging is a function of the free
flow of the exhaust pulse, a design such as the
CC
INSERTS
does not negate the scavenging effect of
an uninterrupted pulse.
The unit is so compact that the
Insert
is only about 7” long and can be cut even shorter if
needed. For racing or street use you only need one
Insert
in each collector or exhaust pipe.
CC INSERTS
are sold in either a race or street
version. The street version has one more Cooling chamber
than the race version, yet is only slightly more
restrictive. For those who wish a drop-in muffler the
insert can be ordered in a typical round case, 3 ½” in
diameter for most uses, and are coated with TECH LINE
COATINGS, INC.,
CERMAKROME
which provides a near chrome finish. The
Inserts
are also available in a canister that fits over the end
of a collector for racing applications and steps up the
size of the insert. If you have a 3” diameter collector
you can use a 3” to 3 ½” canister. This allows the
larger 3 ½” insert to be run. This is particularly
important where the collector diameter is smaller than
ideal.
What is really neat is that you can build
an exhaust system where NO MUFFLERS are needed. You can
do away with the big clunky, inefficient boxes that hang
under the car. Ground clearance improves and you can
route the pipes wherever you wish without worrying about
where to place this big box. Pipes can be located closer
to the body than previously possible giving even better
ground clearance. You can more easily “ slam” the car
since you do not have to allow for the thickness of a
muffler. The weight saving is worth a significant amount
as well. Several street rod customers are using the
Inserts
in "zoomies” and are running with no mufflers at all.
Picture what appears to be open pipes on the street. You
can run side exhaust or “lakes pipes” without running
the exhaust through a muffler. The way exhaust systems
are going to be built in the future is going to be
dramatically effected by this new design.
How efficient are they? After all if they
cost power looks alone won’t sell them. In an
independent test a 383 cu.in. small block Chevy was dyno
tested with open headers and with both race and street
Inserts
installed. The goal of the test was to see what gain in
mid range could be accomplished. The upper RPM cut off
point was 4000 RPM’s. The results? At 3000 RPM the
street
Insert
produced over 3 H.P. more than open headers at 3500 RPM
9 H.P. more and at 4000 RPM 6 H.P. The maximum gain was
at 3800 RPM where 11 H.P. and 8ft.lbs. of torque were
gained over the open header. The race unit only made
about 3 H.P. more than the street version. The
Inserts
were placed directly in the collectors. Remember, if you
had been testing with stock mufflers the gains would be
much, much higher. Imagine running on the street with a
car that makes more useable power than if your headers
were open, and not just at the low end where a little
back pressure helps, but in the mid range as well. Of
course saving weight over mufflers is worth even more
power, and some performance mufflers can weigh more than
20 lbs. each. How did the Inserts perform in a real
world application?
The inserts were used in a rear engine dragster. The
dragster is running a 406 small block Chevy on alcohol.
The car runs in Super Comp. The MPH dropped about 1 mile
per hour and the ET a few hundredths, less than .05. The
tune up was changed, by leaning out the 850 Carb. a
couple of jet sizes, as the car was running “fatter”
with the inserts. Since this was a Super Comp car they
weren’t concerned about getting the tune up perfect as
they run on an index and simply change the throttle stop
as necessary. It is possible that this car could have
cut off the front insert and still met the sound
requirements, thus reducing the small amount of back
pressure created and further reducing the minimal
performance loss.
The effect of the insert, in an exhaust passage, was
further tested. A fixture was built that mimicked the
flow of a single port through a header and collector.
With the 2 disk insert the flow on the test fixture was
far in excess of the flow numbers generated by the
exhaust valves used as a standard. The comparison was
with a 1.81 exhaust valve in a modified 440 cu.in.,
Mopar head. Interestingly the 3 disk insert also flowed
in excess of the capability of the head. The difference
between the two inserts was less than 10 cfm.
When it comes to sound the Inserts give a
true High Performance effect. In fact they have been
described as sounding just like open headers only quiet.
The
Insert
produces a deep sound with a sharp crisp note. The
design of the Insert is such that most of the higher
frequencies are cancelled out, leaving the deeper lower
tone to dominate. The straight through design gives the
“crisp” note. The higher, “sharper” frequencies are the
most objectionable to both the rule makers and the ear.
As an added feature you can adjust the level of sound
that you desire. Each
Insert
comes with a plug and a restrictor. These
items can be tack welded on for the most sound
suppression. If you do not use the plug, which diverts
more air through the ‘cooling” chambers, you get an
increased level of sound. If you use the inserts without
either part you have the loudest note. Even at their
loudest setting the units are still very acceptable for
the street. You get to make the choice you are not stuck
with only one level of sound, as you are with most
designs.
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