Exhaust System Basics - Hot Bike Tech

Last month we concluded a twopart installment article about the induction system. This month we will look at exhaust systems. An optimized exhaust system is critical for maximized engine performance. A few decades ago, there was little development work done on V-Twin exhaust systems. When development work was done, most was performed by the cut-and-try methods. However, with the advent of the rear wheel dynamometer and the increased popularity of the Harley V-Twin after the introduction of the Evolution motor, exhaust system development flourished. Today, there are a plethora of exhaust systems available. When selecting a system, riders typically want a richsounding exhaust note and bitchin' looks that grab their attention. Riders also want real-world performance over a wide rpm range, from slow rpm trolling through the park to crisp acceleration when they whack open the throttle from a standing stop or for passing an 18-wheeler.

Nevertheless, there is no free lunch when it comes to exhaust systems. Tradeoffs exist between looks and performance because exhaust system design has a significant impact on engine performance. Header pipe diameter, pipe length, bend radius, muffler volume, and even baffle design affect performance. Make the pipe too long or too short, too big or too small in diameter, and performance suffers. Performance also suffers when airflow is restricted by the mufflers. Large displacement engines generate more exhaust and require higher-flowing mufflers than small engines, but aesthetics often suffer as muffler size increases. Designing a pipe for street riding is much more difficult than for racing because aesthetics are more important and the powerband is much wider.

Buying an exhaust system can be a daunting experience. For example, there is a overwhelming selection of exhaust system designs, from staggered 2-into-2s, 2-into-1s, and true duals for baggers to straight pipes, big and small diameter headers, short and long header lengths, and stepped headers, just to mention a few. Not surprisingly, it is hard to determine what pipe works best, let alone which one looks best. Then there are a multitude of engine displacements from 74-cubic inchers to 130-inchers and even larger that have varying performance requirements. And the larger the engine displacement, the more difficult it is to find a pipe with sufficient flow for good top-end power. Lucky for us, today we have reliable dyno charts to reference before plunking down our hard-earned cash on a fancy-looking pipe

In order to make stout power, an engine needs adequate airflow. Yet large engines generate a greater volume of exhaust gases, which requires larger volume mufflers and header pipes. Additionally, no exhaust system can deliver optimized power across the entire rpm range. Add a multitude of design options into the selection process, and pipe choice becomes confusing and time-consuming. Since optimum pipe design is determined by an engine parts combination and its most important rpm range, having a basic understanding of the exhaust process will provide you with valuable information for selecting your next exhaust system.

Exhaust System Elements
The exhaust system is an integral part of the components that regulate airflow through the engine. Other key components include the induction system, cylinder heads, and camshaft. To achieve maximum performance, these components must be tuned together as a system for maximum performance within a given rpm range. If one component is changed or modified, the entire group of components must be retuned for maximum performance.