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.
What makes these Inserts so effective? The design seems simple at first. Lets examine what happens to the exhaust pulse as it reaches the Insert. First a portion of the flow moves directly through the center tube, the balance is directed through the first disk. This creates a higher pressure zone in the area outside of the center tube. The result is that the air flow through the center tube is now faster, creating a low pressure zone in the tube. Since the tube is louvered a portion of the air that passes through the first disk is drawn back into the center tube. This helps draw more air through the first disk, thus reducing the back pressure created when the air first encounters this disk. By drawing slower moving, cooler air back into the center tube we reduce sound. Cooler air is “quieter” than hot air. The remaining air that is not drawn into the center tube flows through the next insert, thus slowing the flow and cooling this air even further. Then the difference in pressure between the two air flows pulls additional, “cooler” air back into the center tube. This further reduces the sound of the exhaust gases. If a three disk unit is used the same process is repeated. When the last disk has been passed the remaining air flow exiting the tube, but not drawn into it, mixes with the air flowing out of the center tube further cooling the air. This design not only cools the exhaust gases, to reduce sound, but by mixing the separate air flows multiple times, further reduces the sound emitted.