2 Stroke
In a two-stroke engine a certain amount of exhaust pressure is needed to prevent unburned fuel/air mixture from passing right through the cylinders into the exhaust. This is achieved by the expansion chamber connected to the exhaust port of the engine. The expansion chamber consists of 5 main sections: Header, Diffuser or Inverter cone, Mid section, Baffle cone and finally a Stinger. As exhaust is pushed through the header into the diffuser cone a negative pulse is created, pulling fuel from the engine. Once exhaust enters the mid section, baffle cone and stinger, a positive pulse is created which sends a percentage of the exhaust wave back towards the engine and a certain amount out through the stinger. The stinger acts as a “pressure bleed valve” creating a “plugging effect” necessary for the expansion chamber to perform as designed. An oversized stinger evacuates to much pressure (heat) and an undersized stinger creates to much pressure (heat). As the exhaust wave has not yet reached the atmosphere, the same holds true for the muffler. The muffler acts as an extension of the stinger and must maintain the correct pressure (plugging effect) or performance levels will suffer as a result.
General thinking for a performance muffler is that bigger (more flow) is better. While this is true to a point on a 4 stroke engine, this is not the case on a 2 stroke. A 2 stroke muffler must be tuned to the expansion chamber to provide proper flow characteristics for optimum performance.
When it comes to tuning a two stroke, lets face it the OE’s now what there doing. For an aftermarket company to truely make additional power by just adding a muffler, the engine has to be run slightly leaner. This is accomplished by designing a slightly more restrictive, that’s right, restrictive muffler that creates more heat. It’s a fine line and any gains are minimal at best, usually going unnoticed in the real world.
At GGB our mufflers are designed to be a direct replacement for the stock unit and come with a performance guarantee. What we ultimately provide you with is the chance to drop a lot of under hood weight and the choice of how you want your machine to sound. Because lets face it, the stock muffler leaves a lot to be desired.
4 Stroke
As we mentined, bigger is better when it comes to exhaust flow on a 4 stroke motor. While this is true to a point, bottom end power and fuel economy can suffer from to loose of an exhaust (to much flow). Exhaust temperatures inside a tube can very significantly, from as high as 500 to 1300° F with the average sonic wave traveling at approximately 1700 feet per second in the upper rpm’s. Hot exhaust gas travels at a higher rate of speed than cool gas, so, if an exhaust systems tube diameter (flow) is to large for the engine’s displacement, the exhaust wave slows down, does not scavange spent fuel effectively and therefore reducing overall performance.
For the best overall performance, all GGB 4 stroke mufflers on this site are designed and built specifically for stock and improved stock engines. If you have a heavy mod engine, contact us about a high flow muffler for your application.
Silencing Methods
After correct flow characteristics are determined we address the sound attenuation of the muffler. While there are numerous different muffler designs available on the market, most mufflers for internal combustion engines use passive silencing methods. These muffers fall into two general categories, reactive and dissipative. Reactive mufflers make use of seperate chambers and defelctors to direct sound back to the source and are generally better at reducing low frequency sound waves. These mufflers are generally larger in size and come as original equipment from the manufacturer as they effectively reduce sound throughout a wide rpm range. Dissipative mufflers generally utilize a straight through flow design with perforated screen and filler materials (packing) scrubbing off sound waves and transforming them into heat. This type of muffler is generally smaller, can be easily made to provide more flow an is usually best at reducing medium to high frequencies. As rpm’s climb, so do the sound levels with this type of muffler.
