The unique sound produced by Harley-Davidson V-twin engines, often described as a "fluttering boom," is primarily attributed to a combination of design factors and engineering choices made by the company. These factors include the firing order, engine configuration, and exhaust system design.
Harley-Davidson motorcycles typically use a 45-degree V-twin engine configuration, where the two cylinders are positioned at a 45-degree angle to each other. The firing order of the cylinders is uneven, known as a "180-degree crankshaft" design. This means that the two cylinders fire at irregular intervals, creating a distinctive rhythmic pattern.
The uneven firing order, coupled with the V-twin configuration, creates a pulse of power and torque delivery that contributes to the characteristic sound. The firing sequence produces an uneven exhaust note, resulting in the "fluttering boom" sound at idle and low RPMs. This unique sound has become a recognizable trademark of Harley-Davidson motorcycles and is often associated with their brand identity.
Additionally, Harley-Davidson motorcycles often feature large displacement engines with relatively low RPM ranges, which can contribute to a deeper, lower-pitched sound compared to higher-revving engines. The exhaust system design and the use of various mufflers and baffles also play a role in shaping the sound profile of the motorcycle.
It's worth noting that each motorcycle manufacturer may have its own approach to engine design and sound characteristics, leading to differences in the sound produced by V-twin engines. Therefore, other V-twin motorcycles from different brands may have distinct sound characteristics that can vary from Harley-Davidson motorcycles.