Jan. - Feb. 1999 Lane Racing And Rodding Article By Jim Kaekel, Jr.
With the population continuing to spread out into the rural areas, many race track owners have found themselves facing noise ordinances imposed by city, county, and township governments.
Circle track owners and racers in some areas have been dealing with these ordinances for several years now, but for drag strip owners, limiting the number of decibels (sound measurement units) that a drag car can produce is a new game. Since the easiest and most effective method of limiting the sound of any race car is to install mufflers, a great deal of research is being applied to mufflers designed specifically for circle track and drag racing.
Some circle track sanctioning bodies, ASA for example, have even gone to the extent of requiring a "spec" muffler - one muffler that must be used by every car. The National Hot Rod Association began requiring mufflers on all Super Comp, Super Gas and Super Street drag cars - only at national events - at the onset of the 1998 season. When the 2000 NHRA season begins, the aforementioned classes, as well as Super Stock and Stock Eliminator cars, will be required to use mufflers at national AND divisional levels. Keeping in mind NHRA's maximum limit of 95 decibels - measured at a right angle fifty feet from the car with the engine at 3500 RPM - several manufacturers have developed drag race only mufflers. Meanwhile, racers have begun trying to determine which muffler will fit and keep horsepower loss to a minimum.
With racing mufflers it's a matter of having your cake and eating it too. Racing and OEM mufflers both must reduce noise, but racing versions must also allow an engine to operate in a much higher RPM range while still producing substantial horsepower. Not an easy task, because restriction of noise means an increase in backpressure.
Exhaust noise is a direct result of the combustion process. During each cylinder's cycle, an exhaust "pulse" is created which exits through the exhaust valve, passes through the exhaust port and into the header. It then becomes the muffler's duty to absorb the pulse, which the human ear perceives as a sound wave. Muffling, or sound wave cancellation, is achieved through a series of baffles and passages inside the muffler. Sizes of the baffles and passages are determined by the specific application and RPM range of the particular race engine.
Backpressure exists when muffler flow is less than flow from the exhaust port. Restricting flow in a muffler with baffles will, in effect, send some of the exhaust flow backwards through the system, creating backpressure. An 8" long muffler with 3-1/2" inlet and outlet, and a case diameter of 4", will not create much backpressure, but it won't significantly reduce the decibel level of a big block either. Remember that the larger the muffler, the more surface area there is to absorb noise. Premium racing mufflers will not only have large inlets and outlets for backpressure reduction, but will also have large cases to accommodate less restrictive baffles, and provide maximum noise absorption.
Circle track cars, from factory stocks to late models, commonly use either a 2-into-1 or an auger style muffler. 2-into-1 mufflers use a special "Y"-pipe which joins each collector to a single 5" muffler inlet. Auger mufflers have baffles which actually resemble augers. As the exhaust gases spiral through these baffles, the sound is broken up and noise is reduced. In addition to Howe, which manufactures the 2-into-1 mufflers, Dynomax, Schoenfeld, Supertrapp, Borla, Allstar, and Flowmaster also offer mufflers for circle track racing.
Drag race muffler technology is relatively new and has not had the development time of the circle track mufflers. Pretty much typical of current offerings are the collector/muffler packages offered by both Borla and Flowmaster. These are basically four-into-one slip on collector systems with built-in mufflers that replace the traditional collector. They can be secured by tack-welding or using traditional header tabs and bolts. Borla's XR-1 collector/muffler, constructed of stainless steel for maximum life, is available for headers with primary tube sizes from 1-3/4" to 2-1/2" and outlet sizes of 3" or 4". Flowmaster Scavenger Series collector/mufflers, which use traditional steel construction, are available for headers with primary tube sizes from 1-3/4" to 2-5/8" and outlet sizes of 3" to 5". Dynomax, also a major manufacturer of race mufflers, offers Race Magnums designed specifically for drag racing.
Purchasing a racing muffler is similar to purchasing a performance camshaft. Consult with knowledgeable sales personnel when trying find the proper racing muffler for your application. Application, engine size, RPM range, horsepower output and the type of racing should all be considered during the selection process.