People can read this and decide for themselves.
The Art of Noise:
Designing Sound Characteristics
Into a Motorcycle Engine
Joel Moser
Early on a cloudless July morning in America's Great Plains, a farmer, clutching his warm cup of coffee, walks toward one of his tractors as he begins his work day. Before he reaches his goal, he hears the crisp exhaust note of a motorcycle, and out of the corner of his eye he notices a single headlight cresting the hill of the U.S. Highway that runs adjacent to his field. Long before the motorcycle gets close enough for him to read the name on the gas tank, the farmer knows that he is sharing this early morning moment with a rider aboard a Harley-Davidson, simply because of what he is hearing.
The Harley-Davidson Motor Company has re-emerged as the leader in the heavyweight motorcycle industry because of countless stories of concise product recognition similar to this one. While improving the quality of their product line, the Motor Company has remained faithful to the styling cues that it was built upon, and in doing so has created an identity by which the rest of the cruiser genre is judged. Just what are some of these styling cues? Many of them are visual, like "Springer" front suspensions, peanut-shaped fuel tanks, and finned V-twin engines. And some are audible, for as Jon Thompson [1994] explains, "An essential element of the H-D equation is the charismatic feel and sound of the Harley engine--a sound one Honda spokesman characterized as, no kidding, 'potato-potato-potato!' "
While this may not sound like the most flattering of descriptions, it is one that Harley has embraced completely, and takes very seriously. It is a cornerstone of their marketing strategy, for even their product guide exclaims:
Just how is an exhaust note designed to "sound like a Harley?" What parameters govern such a design requirement? Answering these questions is an everyday experience for some of the engineers at the Harley-Davidson Motor Company, and their effectiveness in garnering solutions to them helps ensure their product's continued success in the marketplace.
Design Parameters
The exhaust rumble that is created by a running motorcycle engine is a very complex sound, and it is one whose origin is equally complex. Beginning before the combustion process and ending with the muffling of the exhaust, the tone of the sound that is ultimately heard by the customer is one that has been influenced by a great number of parameters. Many decisions are made with a special cognizance of their effect on this tone, and when they are coupled together the result is, according to Harley, "the way a motorcycle ought to sound." While all of these design decisions contribute to this characteristic exhaust sound, only a small number of them are regarded as absolutely essential to it. Thus, a closer investigation of these critical ones is truly necessary in order to obtain a more complete understanding of the origin of this styling cue, this "Harley sound."
Carburation and Ignition. While one may intuitively think that tonal exhaust characteristics begin with the combustion process, they actually begin to evolve even before that. As air and fuel mix in the carburetor and enter the cylinder on the intake stroke, these tonal qualities are being influenced and developed. This influence is a subtle one, yet it is one that is noticeable enough that Harley's engineers must take it into account when citing the origins of their sound.
The typical modern motorcycle uses an individual carburetor for each of its cylinders. This design increases overall engine performance, including responsiveness and horsepower, and as a result virtually every motorcycle imported into this country today includes a bank of multiple carburetors to serve its intake needs. Harley-Davidsons, in contrast, use a single carburetor with a shared intake manifold to supply both cylinders with air and fuel. Most manufacturers consider this design to be rather dated, but Harley has chosen to stay with it for a number of reasons. These include a reduction in complexity and a cleaner visual appearance, as well as the creation of a noticeable unevenness in the exhaust rumble. This final reason is due to the fact that this dual intake strongly affects the air/fuel pressure waves and their induction into the cylinders, since varying pressure waves are forced to be superimposed on one another. A characteristic unevenness develops here because of this, and it continues all the way through the combustion and exhaust processes.
This unevenness is further accentuated by another of Harley's designs that most manufacturers would consider dated. While today's motorcycle manufacturers typically use individual ignition coils for each of the cylinders in their engines, Harley-Davidson continues to use only one coil to serve the needs of two cylinders. This means that the sparkplugs can not be controlled separately--both plugs fire at the same time, regardless of whether it is that cylinder's combustion stroke or not. Thus, the sparkplugs in a Harley are firing twice during a complete engine cycle--once on the combustion stroke and once on the exhaust stroke. While one cylinder is beginning its combustion stroke and sparking, the other is beginning its exhaust stroke and also sparking. This spark on the exhaust stroke is known as a "wasted spark" [Bub, 1995], and since there is a minute amount of unburned fuel in the exhausting cylinder, this "wasted spark" creates a partial detonation. This partial detonation is important not only from an emissions standpoint but also from an acoustics standpoint, because it definitely contributes to exhaust unevenness.
Just how important is this slight unevenness to "the Harley sound?" Interestingly, it is lost in some of the new Harley-Davidsons, because of the advent of fuel injection. These fuel-injected models sound very similar to their predecessors, but since they do not use these older designs just mentioned, there is a subtle component missing. Subtle yes, but certainly still noticeable, and Harley has already heard of a case where a man asked to trade in his brand new fuel-injected model for a new carburated one, simply because his wife said it didn't sound quite right. [Moser, 1995]
Engine Architecture and Crankshaft Design. While the design decisions surrounding the air/fuel induction into the cylinder are clearly important to creating unique tonal characteristics, it is the decisions surrounding the combustion process that are of primary importance. In particular, the use of a single-pin crankshaft in a 45° V-Twin is perhaps the single most important parameter to consider while trying to explain the origins of the "Harley sound," for this combination results in a unique engine timing diagram and a unique elopeness that directly translate into the tonal characteristics that Harley cherishes. (Emphasis mine) This combination is no secret, for as Jon Thompson explains:
As is the case with the carburation and ignition systems on a Harley, this single crankpin design is a very old one. Harley has been using its "fork and knife" version of it since 1909, and no other manufacturers have consistently used the "fork and knife" since Indian and Vincent did in the 1950's [Bleustein, 1995]. The fact that the majority of the industry has migrated to newer designs is not surprising, because the "fork and knife" is inherently weak due to stress concentrations in the outer connecting rod. These stress concentrations are certainly a concern to Harley, but not enough to cause the company to abandon the design. In fact, Harley sees this design as a part of their heritage, and point to it as a link to their storied past. Such attention to history breeds a consistency in product evolution, and this evolution has greatly helped in maintaining the familiar "potato-potato-potato" sound.
Exhaust and Muffler Design. What other parameters are involved in creating Harley's uniquely identifiable exhaust sound? While decisions involving carburation and the use of a single-pin crankshaft are two of them, there is certainly more to this formula. The exhaust and muffler assembly is also an essential ingredient.
Harley-Davidson uses only three different muffler designs to serve the needs of all of their models. The first of these is a plug muffler and is used on all of the 883cc Sportster models built for the U.S. market. Another is also a plug muffler for 883cc Sportsters, but it is used for models going to international markets. And the third design, a muffler internally similar to an automobile muffler, is used on all of the 1340cc models regardless of product destination.
The basic design of the plug muffler is an old one, but it is one that is still widely accepted by the motorcycle industry as a whole. Essentially, as exhaust gases are pushed out of the cylinder and down the exhaust tube, they are forced through a perforated screen and into a section of fiberglass, where the majority of noise reduction takes place. After moving through the fiberglass, the gases are forced through another set of holes and are then exhausted to the atmosphere. Variations of this design are used worldwide for many applications, and Harley-Davidson has consistently used it to meet their needs as well.
Based on data obtained through years of testing, Harley engineers have chosen to use eight rows of holes in the section before the fiberglass in order to optimize horsepower. They have also chosen to use either four rows (for domestic models) or two rows (for international models) of holes to the rear of the fiberglass in order to optimize noise emission. All of this was done while keeping in mind the overall goal of the muffler, which involved maintaining the frequency content in the noise emission that has become synonymous worldwide with Harley-Davidsons. The tone of this frequency content, often described as "guttural," is the result of the mufflers reducing the high frequencies while keeping the lower ones, and the fiberglass within the muffler section serves this purpose splendidly. The result is the throaty "potato-potato-potato" sound that the Honda spokesman described earlier.
But the plug muffler is not the only way to achieve this sound. The larger motorcycles in Harley's line use a muffler design that is more car-like in that it uses a series of sharp internal bends to slow the gas flow and reduce noise. The resulting noise emission contains more of the higher frequencies, but enough reduction takes place that the tone is nearly identical to the tone of the others. The only drawback to this design is that these tubing bends necessitate a larger diameter muffler, but this is regarded as an acceptable tradeoff because the tonal quality of the exhaust still provides the ubiquitous sound that Harley is known for.
Other Considerations
There are, of course, other sources that could be considered when investigating the origins of the "Harley sound." For example, one may think that the design of the camshaft may be important, since it is responsible for the actuation of the valves. This design is valid in that the camshaft affects the percentage of time that the exhaust valves would be open, or more importantly for this purpose, closed. The timing of the valve closing determines the percentage of time that exhaust gas pressure pulses can move up and down the exhaust pipe with closed-end termination on the engine side and the open atmosphere on the other side. These pulses move at a frequency that is certainly important to the final exhaust sound [Munjal, 1987], but this frequency has been found to be a function of the crankshaft and not of the camshaft. Because of this, camshaft timing is not critical to exhaust tonal quality, and Harley-Davidson has been able to use different camshafts in different applications without any distinguishable change in the qualities of their exhaust.
Another source of noise that is not considered to be a large factor is what is known as "shell noise." This noise is generated by the exposed surfaces of the vibrating engine and mufflers and is due to the vibration characteristics inherent to their operation. This noise is certainly not the primary component of the sound the customer enjoys, but it is a small part, and it is something that acoustic engineers worldwide are aware of. For example, at the 1995 Small Engine Technology Conference in Milwaukee, engineers from Kawasaki presented their research in this area, and demonstrated how it was now possible for them to predict the vibration mode and noise emission from their engine covers in the computer-assisted design phase ["When Mechanics," 1995]. This research of course has no direct bearing on the shell noise characteristics of other manufacturers, but it certainly illustrates how this phenomenon can be a priority to an engine design team concerned with sound quality.
Conclusion
Because the Harley-Davidson Motor Company intimately understands the cruiser genre of motorcycle, the company is currently enjoying an enormous amount of commercial success. By focusing on style as well as function and by incorporating nostalgia into modern technology, Harley has created a product line that is admired by its customers and emulated by its competitors for its timeless qualities. These styling cues are numerous in number and varied in nature, but taken as a whole they represent that which "makes a Harley a Harley." A distinct exhaust sound is just one example of these, and this closer examination of the design parameters involved in such a requirement shows just how seriously Harley takes these styling cues. From the carburetor to the muffler, design decisions are closely scrutinized to determine not only their performance, but also their impact on the visible and audible characteristics of the finished product. Such close scrutiny has led to strong sales, and this type of scrutiny is only now being employed by the other major manufacturers of the world. While the success of the competition's new models is yet to be determined, one thing seems clear: unless they satisfy the customer's eyes and ears as well as Harley-Davidsons do, Harleys will continue to dominate this segment of the motorcycle industry.
References Cited
Bub, Alex, Project Coordinator--Powertrain Development, Harley-Davidson Motor Company (23 December 1995), personal interview.
Bleustein, Jeffrey, "The Unique Harley-Davidson Sound," The Enthusiast (Fall 1995), p. 6.
1994 Product Guide (Milwaukee: Harley-Davidson Motor Company, 1994). pp.3-4.
Moser, Christopher, mechanic (23 December 1995), personal interview.
Munjal, M. L., Acoustics of Ducts and Mufflers (New York: John Wiley and Sons, 1987), pp. 104-108 & 285-296.
Savage, Mark, "Harley Trademark Attempts Making Some Noise," Milwaukee Journal Sentinel (November 2, 1995), pp.1D-3D.
Thompson, Jon F., "1995 Honda American Classic Edition--Honda Hones the Harley Formula," Cycle World (September 1994), pp. 44-45
"When Motorcycle Engineers Talk Shop," Roadracing World (November 1995), p. 3.
References Consulted
Elkins, Charles, "Environmental Impact Statement for the Noise Emission Regulations for Motorcycles and Motorcycle Exhaust Systems," (Washington: U.S. EPA Office of Noise Abatement and Control, December 1980).
Stermer, William, "No Cliche Cruiser," Rider (November 1995), p. 25.
Author's Note:Joel Moser is a senior in mechanical engineering at the University of Wisconsin-Madison. After graduation, he hopes to work in the motorcycle industry as a design engineer. This essay won the 1996 Steuber Prize Award. (Back to Beginning)
The Art of Noise:
Designing Sound Characteristics
Into a Motorcycle Engine
Joel Moser
Early on a cloudless July morning in America's Great Plains, a farmer, clutching his warm cup of coffee, walks toward one of his tractors as he begins his work day. Before he reaches his goal, he hears the crisp exhaust note of a motorcycle, and out of the corner of his eye he notices a single headlight cresting the hill of the U.S. Highway that runs adjacent to his field. Long before the motorcycle gets close enough for him to read the name on the gas tank, the farmer knows that he is sharing this early morning moment with a rider aboard a Harley-Davidson, simply because of what he is hearing.
The Harley-Davidson Motor Company has re-emerged as the leader in the heavyweight motorcycle industry because of countless stories of concise product recognition similar to this one. While improving the quality of their product line, the Motor Company has remained faithful to the styling cues that it was built upon, and in doing so has created an identity by which the rest of the cruiser genre is judged. Just what are some of these styling cues? Many of them are visual, like "Springer" front suspensions, peanut-shaped fuel tanks, and finned V-twin engines. And some are audible, for as Jon Thompson [1994] explains, "An essential element of the H-D equation is the charismatic feel and sound of the Harley engine--a sound one Honda spokesman characterized as, no kidding, 'potato-potato-potato!' "
While this may not sound like the most flattering of descriptions, it is one that Harley has embraced completely, and takes very seriously. It is a cornerstone of their marketing strategy, for even their product guide exclaims:
Potato, Potato, Potato. . . A Harley-Davidson at Idle. Has the wind ever carried a more satisfying sound?...The sound is unmistakable. The signature of a Harley-Davidson motorcycle... you instinctively know: this is the way a motorcycle ought to sound... This did not happen by accident... when we find something more pleasing than anything else, we stick with it. Like the exhaust note of a Harley-Davidson 45° V-twin, the sweetest sound ever carried on the wind. [Thompson, 1994]
Clearly, Harley believes that their V-twin exhaust rumble is instantly recognizable and discernible to the trained ear, and believes that it is a vitally important component of their strong product identity. Because of this, their design engineers are asked to create products that are technologically competitive and yet wonderfully nostalgic -- essentially, they are asked to design with an eye toward the future and an eye toward the looks and sounds of motorcycles long past. Just how is an exhaust note designed to "sound like a Harley?" What parameters govern such a design requirement? Answering these questions is an everyday experience for some of the engineers at the Harley-Davidson Motor Company, and their effectiveness in garnering solutions to them helps ensure their product's continued success in the marketplace.
Design Parameters
The exhaust rumble that is created by a running motorcycle engine is a very complex sound, and it is one whose origin is equally complex. Beginning before the combustion process and ending with the muffling of the exhaust, the tone of the sound that is ultimately heard by the customer is one that has been influenced by a great number of parameters. Many decisions are made with a special cognizance of their effect on this tone, and when they are coupled together the result is, according to Harley, "the way a motorcycle ought to sound." While all of these design decisions contribute to this characteristic exhaust sound, only a small number of them are regarded as absolutely essential to it. Thus, a closer investigation of these critical ones is truly necessary in order to obtain a more complete understanding of the origin of this styling cue, this "Harley sound."
Carburation and Ignition. While one may intuitively think that tonal exhaust characteristics begin with the combustion process, they actually begin to evolve even before that. As air and fuel mix in the carburetor and enter the cylinder on the intake stroke, these tonal qualities are being influenced and developed. This influence is a subtle one, yet it is one that is noticeable enough that Harley's engineers must take it into account when citing the origins of their sound.
The typical modern motorcycle uses an individual carburetor for each of its cylinders. This design increases overall engine performance, including responsiveness and horsepower, and as a result virtually every motorcycle imported into this country today includes a bank of multiple carburetors to serve its intake needs. Harley-Davidsons, in contrast, use a single carburetor with a shared intake manifold to supply both cylinders with air and fuel. Most manufacturers consider this design to be rather dated, but Harley has chosen to stay with it for a number of reasons. These include a reduction in complexity and a cleaner visual appearance, as well as the creation of a noticeable unevenness in the exhaust rumble. This final reason is due to the fact that this dual intake strongly affects the air/fuel pressure waves and their induction into the cylinders, since varying pressure waves are forced to be superimposed on one another. A characteristic unevenness develops here because of this, and it continues all the way through the combustion and exhaust processes.
This unevenness is further accentuated by another of Harley's designs that most manufacturers would consider dated. While today's motorcycle manufacturers typically use individual ignition coils for each of the cylinders in their engines, Harley-Davidson continues to use only one coil to serve the needs of two cylinders. This means that the sparkplugs can not be controlled separately--both plugs fire at the same time, regardless of whether it is that cylinder's combustion stroke or not. Thus, the sparkplugs in a Harley are firing twice during a complete engine cycle--once on the combustion stroke and once on the exhaust stroke. While one cylinder is beginning its combustion stroke and sparking, the other is beginning its exhaust stroke and also sparking. This spark on the exhaust stroke is known as a "wasted spark" [Bub, 1995], and since there is a minute amount of unburned fuel in the exhausting cylinder, this "wasted spark" creates a partial detonation. This partial detonation is important not only from an emissions standpoint but also from an acoustics standpoint, because it definitely contributes to exhaust unevenness.
Just how important is this slight unevenness to "the Harley sound?" Interestingly, it is lost in some of the new Harley-Davidsons, because of the advent of fuel injection. These fuel-injected models sound very similar to their predecessors, but since they do not use these older designs just mentioned, there is a subtle component missing. Subtle yes, but certainly still noticeable, and Harley has already heard of a case where a man asked to trade in his brand new fuel-injected model for a new carburated one, simply because his wife said it didn't sound quite right. [Moser, 1995]
Engine Architecture and Crankshaft Design. While the design decisions surrounding the air/fuel induction into the cylinder are clearly important to creating unique tonal characteristics, it is the decisions surrounding the combustion process that are of primary importance. In particular, the use of a single-pin crankshaft in a 45° V-Twin is perhaps the single most important parameter to consider while trying to explain the origins of the "Harley sound," for this combination results in a unique engine timing diagram and a unique elopeness that directly translate into the tonal characteristics that Harley cherishes. (Emphasis mine) This combination is no secret, for as Jon Thompson explains:
That characteristic sound and rhythm [of a Harley] is the result of both connecting rods... being driven off of a single crankshaft pin. The [Honda] Shadow... has two crankpins, oriented 90° apart. That's a better way to quell the engine's dynamic forces, but it doesn't reproduce the sound of nostalgia. [Thompson, 1994]
This being the case, it should not come as a surprise that every model in the Harley lineup this year, as in years past, is based on a 45° V-twin with a single pin crankshaft. Nor should it be surprising that when Honda engineers developed their new American Classic Edition (ACE), a cruiser intended to directly appeal to potential Harley riders, their "first change (for the ACE) was to adopt a single crankpin in a successful effort to capture the traditional American sound" [Thompson, 1994]. Based on this new design, Tim Hoelter, vice president and general council of H-D, was prompted to publicly accuse Honda of introducing an engine that purposely mimics the Harley sound. [Savage,1995] As is the case with the carburation and ignition systems on a Harley, this single crankpin design is a very old one. Harley has been using its "fork and knife" version of it since 1909, and no other manufacturers have consistently used the "fork and knife" since Indian and Vincent did in the 1950's [Bleustein, 1995]. The fact that the majority of the industry has migrated to newer designs is not surprising, because the "fork and knife" is inherently weak due to stress concentrations in the outer connecting rod. These stress concentrations are certainly a concern to Harley, but not enough to cause the company to abandon the design. In fact, Harley sees this design as a part of their heritage, and point to it as a link to their storied past. Such attention to history breeds a consistency in product evolution, and this evolution has greatly helped in maintaining the familiar "potato-potato-potato" sound.
Exhaust and Muffler Design. What other parameters are involved in creating Harley's uniquely identifiable exhaust sound? While decisions involving carburation and the use of a single-pin crankshaft are two of them, there is certainly more to this formula. The exhaust and muffler assembly is also an essential ingredient.
Harley-Davidson uses only three different muffler designs to serve the needs of all of their models. The first of these is a plug muffler and is used on all of the 883cc Sportster models built for the U.S. market. Another is also a plug muffler for 883cc Sportsters, but it is used for models going to international markets. And the third design, a muffler internally similar to an automobile muffler, is used on all of the 1340cc models regardless of product destination.
The basic design of the plug muffler is an old one, but it is one that is still widely accepted by the motorcycle industry as a whole. Essentially, as exhaust gases are pushed out of the cylinder and down the exhaust tube, they are forced through a perforated screen and into a section of fiberglass, where the majority of noise reduction takes place. After moving through the fiberglass, the gases are forced through another set of holes and are then exhausted to the atmosphere. Variations of this design are used worldwide for many applications, and Harley-Davidson has consistently used it to meet their needs as well.
Based on data obtained through years of testing, Harley engineers have chosen to use eight rows of holes in the section before the fiberglass in order to optimize horsepower. They have also chosen to use either four rows (for domestic models) or two rows (for international models) of holes to the rear of the fiberglass in order to optimize noise emission. All of this was done while keeping in mind the overall goal of the muffler, which involved maintaining the frequency content in the noise emission that has become synonymous worldwide with Harley-Davidsons. The tone of this frequency content, often described as "guttural," is the result of the mufflers reducing the high frequencies while keeping the lower ones, and the fiberglass within the muffler section serves this purpose splendidly. The result is the throaty "potato-potato-potato" sound that the Honda spokesman described earlier.
But the plug muffler is not the only way to achieve this sound. The larger motorcycles in Harley's line use a muffler design that is more car-like in that it uses a series of sharp internal bends to slow the gas flow and reduce noise. The resulting noise emission contains more of the higher frequencies, but enough reduction takes place that the tone is nearly identical to the tone of the others. The only drawback to this design is that these tubing bends necessitate a larger diameter muffler, but this is regarded as an acceptable tradeoff because the tonal quality of the exhaust still provides the ubiquitous sound that Harley is known for.
Other Considerations
There are, of course, other sources that could be considered when investigating the origins of the "Harley sound." For example, one may think that the design of the camshaft may be important, since it is responsible for the actuation of the valves. This design is valid in that the camshaft affects the percentage of time that the exhaust valves would be open, or more importantly for this purpose, closed. The timing of the valve closing determines the percentage of time that exhaust gas pressure pulses can move up and down the exhaust pipe with closed-end termination on the engine side and the open atmosphere on the other side. These pulses move at a frequency that is certainly important to the final exhaust sound [Munjal, 1987], but this frequency has been found to be a function of the crankshaft and not of the camshaft. Because of this, camshaft timing is not critical to exhaust tonal quality, and Harley-Davidson has been able to use different camshafts in different applications without any distinguishable change in the qualities of their exhaust.
Another source of noise that is not considered to be a large factor is what is known as "shell noise." This noise is generated by the exposed surfaces of the vibrating engine and mufflers and is due to the vibration characteristics inherent to their operation. This noise is certainly not the primary component of the sound the customer enjoys, but it is a small part, and it is something that acoustic engineers worldwide are aware of. For example, at the 1995 Small Engine Technology Conference in Milwaukee, engineers from Kawasaki presented their research in this area, and demonstrated how it was now possible for them to predict the vibration mode and noise emission from their engine covers in the computer-assisted design phase ["When Mechanics," 1995]. This research of course has no direct bearing on the shell noise characteristics of other manufacturers, but it certainly illustrates how this phenomenon can be a priority to an engine design team concerned with sound quality.
Conclusion
Because the Harley-Davidson Motor Company intimately understands the cruiser genre of motorcycle, the company is currently enjoying an enormous amount of commercial success. By focusing on style as well as function and by incorporating nostalgia into modern technology, Harley has created a product line that is admired by its customers and emulated by its competitors for its timeless qualities. These styling cues are numerous in number and varied in nature, but taken as a whole they represent that which "makes a Harley a Harley." A distinct exhaust sound is just one example of these, and this closer examination of the design parameters involved in such a requirement shows just how seriously Harley takes these styling cues. From the carburetor to the muffler, design decisions are closely scrutinized to determine not only their performance, but also their impact on the visible and audible characteristics of the finished product. Such close scrutiny has led to strong sales, and this type of scrutiny is only now being employed by the other major manufacturers of the world. While the success of the competition's new models is yet to be determined, one thing seems clear: unless they satisfy the customer's eyes and ears as well as Harley-Davidsons do, Harleys will continue to dominate this segment of the motorcycle industry.
References Cited
Bub, Alex, Project Coordinator--Powertrain Development, Harley-Davidson Motor Company (23 December 1995), personal interview.
Bleustein, Jeffrey, "The Unique Harley-Davidson Sound," The Enthusiast (Fall 1995), p. 6.
1994 Product Guide (Milwaukee: Harley-Davidson Motor Company, 1994). pp.3-4.
Moser, Christopher, mechanic (23 December 1995), personal interview.
Munjal, M. L., Acoustics of Ducts and Mufflers (New York: John Wiley and Sons, 1987), pp. 104-108 & 285-296.
Savage, Mark, "Harley Trademark Attempts Making Some Noise," Milwaukee Journal Sentinel (November 2, 1995), pp.1D-3D.
Thompson, Jon F., "1995 Honda American Classic Edition--Honda Hones the Harley Formula," Cycle World (September 1994), pp. 44-45
"When Motorcycle Engineers Talk Shop," Roadracing World (November 1995), p. 3.
References Consulted
Elkins, Charles, "Environmental Impact Statement for the Noise Emission Regulations for Motorcycles and Motorcycle Exhaust Systems," (Washington: U.S. EPA Office of Noise Abatement and Control, December 1980).
Stermer, William, "No Cliche Cruiser," Rider (November 1995), p. 25.
Author's Note:Joel Moser is a senior in mechanical engineering at the University of Wisconsin-Madison. After graduation, he hopes to work in the motorcycle industry as a design engineer. This essay won the 1996 Steuber Prize Award. (Back to Beginning)
