Mud, Sweat and Gears column by Randy Hall courtesy of ATV World Magazine.

Thesubject that we are going to tackle in this issue is the number one reason we are losing riding areas. That reason is the noise expelled by the exhaust systems of our various recreational vehicles. For the most part, this is thought to be a problem for 4 stroke, off-road motorcycles and ATV’s, but this also includes snowmobiles and street bikes. In most cases the manufactured stock exhaust, if properly maintained, is usually in the ball park of acceptable. It is the aftermarket equipment that generally causes the issues.

Although loud engine exhaust noise has always irritated much of the general public, the introduction of the 4 stroke engine is causing even more discomfort to those who weren’t previously happy with the noise situation. So let’s break this subject down. As many of you know, sound travels in a frequency pattern known as sound waves. Two stroke sound waves, which many people feel are louder, are a higher pitch or frequency. These are like the waves on a lake that travel quickly on the surface and once reaching the shore, lose all their energy, quickly dissipate and disappear. The rumble of a four stroke engine coming out the exhaust is a lower pitch but a much stronger wave. Think of it as a tidal wave that once it reaches shore, continues to push much further before the energy of the wave even begins to dissipate. This is due to the shape and frequency of the wave.

Can we control it? Absolutely we can. Part of the problem is that when we purchase an aftermarket exhaust muffler, we have the choice to install the inserts, restrictors and spark arresters that come with it. Although the manufacturer recommends these parts to be installed, for the most part they are not being used because the operator has this idea that louder is more power. Without getting into a completely different subject of engine performance, simply making your exhaust louder will not make your engine stronger or faster. A properly tuned (not louder) exhaust will make your engine work better. This does include the installation of the gizmos that come with your shiny new exhaust. Think about this, why would the manufacturer of the exhaust system you just bought, send you something that would cause your engine to run poorly?

Another misunderstood issue that often rears its head is that people think that inserts are restricting the exhaust too much because the muffler is getting too hot. Well, first off, the general engineering of an exhaust system is sizing it to handle about five times the slug volume that the engine can put out. This means the exhaust system of a 250cc engine can handle about 1250cc of exhaust. Second, a muffler is designed to absorb the high temperature pressure pulses coming from the engine. The more of the pulse it absorbs, the hotter it becomes and the quieter the exhaust entering the environment is. That’s what mufflers do. They get hot when working properly.

This brings up the point that your exhaust system is now more than ever, a maintenance item. You will need to know how to properly repack your muffler at regular maintenance intervals, or have your local dealer or mechanic do it for you. A strong running engine will literally pound out the packing when the engine is running under high power output situations. A high performance four stroke engine will require more exhaust maintenance than a competition two stroke engine of years gone by.

Many competition venues are now requiring sound testing during an event. It won’t be long until practices and riding on public land will follow. There are currently a couple of sound testing procedures used to check the noise level of vehicles. The CMRC is using the SAE J1287 sound test procedure at many of its events to help with noise pollution. This procedure although not perfect, does standardize a process that is helping to control the issue at hand. This test procedure can be purchased from the SAE website or simply found by typing "SAE J1287 Sound Test Procedure" into your favorite search engine.

The procedure using a sound meter at a specified engine rpm basically reads the noise level of the exhaust stream approximately 1 meter behind the outlet of the exhaust system. Those interested in the type of equipment that is used can contact me through ATV World, or contact the CMRC at www.cmrcracing.com. At the pro level of competition in 2010, a reading of 94 dBA is going to be the standard for all classes across the country. A few years ago, it was above 100 dBA, so the exhaust is getting quieter, yet the engines are getting faster and more powerful. So much for the theory of more noise equaling more power.

Here are a couple of more “sound” thoughts to help with the issue at hand. If you are going through a residential area, or even by one house, don’t be on the throttle. Leave that until you are isolated out on the trail. Be wise when picking your riding times as to be more people friendly. I’m not sure about your area, but in my neck of the woods 8:00am Sunday morning could end up causing you some serious bodily harm. A little bit of courtesy can go a long way in keeping a riding area open.

The bottom line is that we all want to have the biggest and baddest machine on the trail. Let’s face it, most stock machines have more power straight out of the crate than most of us mere mortals can handle. If you do decide to use an aftermarket exhaust system, follow the manufacturer’s installation instructions. They know what they are talking about, and how best to make you and your machine happy. As many clubs are using catch phrases like leave tracks, not trash, and tread lightly, we need to be seen and not heard.