The Test Subject

'98 RM250 - modified for Enduro and multi-day trail rides. Acerbis 3.4 gal tank & hand guards, Renthal bars, Works Connection radiator braces, frame guards & skidplate. Maiers USA enduro jug, Stock Suzuki pipe (installed and tested) and FMF "Torque" pipe & TurbineCore II silencer. Still pretty loud

As many of our readers are aware, noise pollution from performance dirt bikes and ATV's on public lands and tracks are a rising concern amongst landowners and other non-mechanized recreationalists, and is increasingly becoming an issue cited when determining management plans for the future. Tracks and other facilities that were once well outside of populated areas are now being encroached upon by expanding developments that are now collectively deciding that they no longer want these noisy neighbors. Thus, the development of quiet series pipes has taken off with a (quiet) bang.

While the last few years have really brought about some significant advances in quiet pipe technology, the focus (with some exceptions) has always been on what is currently popular or widely used. With the explosion in affordable and lightweight high performance four-stroke machines, there isn't as much benefit in development of quiet performance two-stroke pipes as in recent years. The losers in this struggle are folks who have older or less popular bikes, and ultimately everyone. If there isn't a quiet pipe available, there's no way to do the responsible thing. As many pro-access OHV groups have stated over the last 25 years, Less Sound = More Ground.

Fit's most silencers and spark arrestors with an 9 7/8 inch circumference. There appears to some "give" to the snorkel for slightly larger exhausts

Example of Dyno results from the dB Snorkel website

For example, an '04 CR250 was tested by dB Snorkel with both the FMF TurbineCore 2 (91 dB in the 20" SAE J1287 test) and the ProCircuit 304 & Sparky (96 dB in the 20" SAE J1287 test); the addition of the dB Snorkel scrubs 3 dB off the quiet FMF, and 6 dB off the performance ProCircuit. This is pretty impressive stuff, especially considering the results of their dyna-mometer testing with and without the dB Snorkel.

As is so often the case, the inspiration for this product originally came from personal need. In 2000 when dB Snorkel founder and CCC member Sydney Gearing attempted to participate in the Cycle Conservation Club of Michigan's annual "Rights of Spring" ride, he failed to pass the Michigan 94 dB(A) limit sound check with his US Forest Service Approved spark arrestor/silencer.

While the spark arrestor clearly satisfied the federal limit of 99 dB (A) at that time, the silencer simply wasn't going to cut it in his home state; faced with the choice of either a more mild-mannered machine than his current CR 500, or a more restrictive pipe – he chose a third option.

Syd Gearing on the dB Snorkel:

"Aftermarket exhaust manufacturers have done a good job of quieting 2-stroke bikes without robbing power. All the media attention to noise has ended up heightening Public Awareness – Awareness of the Riding Public, but also of the Anti-OHV Public."

"I believe we are now in a situation where, if an Anti-OHV can hear a bike in the woods or on the track, they will want the activity stopped. ?"

"This is where the dB Snorkel comes in. We designed it so that it would fit as many different bikes as possible. It is a combination of function and manufacturing realities. It is for riders concerned with having somewhere to ride. Even a modern bike with a quiet exhaust system could go more places undetected if it was a little quieter – regardless of whether it falls below mandatory noise limits."

Red indicates the normal sound damping occuring in the silencer. Yellow indicates the release through the smaller opening of the "peak" of the exhaust pulse. Light Blue & Blueindicate the path the majority of the exhaust takes through the snorkel for further sound damping

Peak pressure from the exhaust pulse is released from a smaller opening (photo right) in the base of the dB Snorkel, which, like the primary path, is directed toward the ground.

This has the advantages of reducing the overall backpressure of the additional length of the exhaust path, directing the sound towards the ground where more of it can be absorbed, and releasing two out-of-phase exhaust pulses rather than a single larger exhaust pulse.

The packaging was professional quality

I have to say that my initial impression of the dB Snorkel was extremely positive. While dB Snorkel may be a small company, they are obviously very detail-oriented and put in some serious R&D time on this product. The design of the Snorkel itself is appealing to the engineer in me - the twin exhaust ports, the flexible sound absorbing material, and the straightforward no nonsense design? Well OK – it does look a bit funny, but it grew on me.

The packaging and components all looked to be of a very high quality. Probably the most impressive item included was the installation instructions. This was no simple photocopied half-page of text instructions, but a professionally printed poster-size page of obviously well considered instructions and extremely useful illustrations.

Impressive also is that the pre-production product testing was taken extremely seriously. During the testing period of this product, Syd was extremely responsive, shipping out re-thought parts based on comments and their own testing. The releasable zip ties were updated with a more secure permanent zip tie, a change which really doesn't affect temporary removal of the dB Snorkel, but does reduce the possibility of the L-Tube coming loose on its own. Black oxide coated band clamps were substituted for several of the stainless clamps so that they would be less visible against the body of the snorkel.

Installation of the dB Snorkel was a fairly simple process with only a few tools required – whatever you need to remove your side panel from your bike, a phillips screwdriver, a sharp utility blade, and a measuring tape. I say simple providing your silencer has a welded or carefully milled mounting bracket. As with many aluminum-bodied silencers, the FMF TurbineCore II installed on my RM250 has a rib that is extruded with the body and runs the length of the silencer and from which the mount holes are machined. Anyone familiar with mounting an add-on spark arrestor should immediately see the problem: the last inch or so of this rib needs to be filed off to achieve any kind of decent seal.

Extruded aluminum canister with typical mounting "rib"

Note the tiremarks on the silencer and fender. A recent crash necessitated the replacement of the silencer - but the subframe appears also to have bent. This will have to be fixed to provide clearance for the dB Snorkel

I elected to take the path of least resistance and use power tools, but anyone not already familiar with power tools and aluminum should probably follow the instructions and use a good quality mill file to remove the majority of the rib, and a very fine file for the final cleanup. With power tools, it is far easier to take off material than to put it back.

I chose to use an angle grinder with an extremely thin cutting disc to remove the majority of the rib, and then went back over it with a very fine sanding disc to remove some rough edges. Final smoothing and shaping was accomplished with extremely fine flat and round files. I chose to buff out the remaining tool marks on the silencer with a Dremel buffing wheel.

Step 2 from the instructions - preparing the silencer

The thin cutting disk made quick and accurate work of removing the rib

Trimming off the rib

The remainder of the rib was easily removed with a sanding wheel on the angle grinder. The sanding disk was comprised of multiple overlapping layers of medium-fine sandpaper

Final shaping and smoothing were accomplished with a very fine file. After using the power tools, using this seemed like slow work.

Even with the fine file there were significant toolmarks left on the aluminum.

The small Dremel buffing wheel seemed perfect for the job

Finished product

The remainder of the install is not tough or incredibly time consuming, but it wasn't a total piece of cake. There are a number of products out there that I have personally had to modify to fit - and some that fit so poorly I sent the product back. The dB Snorkel it fit and installed as promised. However I highly recommend a careful first reading of the instructions; there are a number of details that can slip by once you have tools in your hands.

For the purposes of this review, all of the photos were taken with the silencer removed from the bike, but it is critical to perform the trial fitting with it mounted to the bike, and it's easier as well.

The heart of the dB Snorkel - the sound-absorbing elastomer Main Body, J-Tube, and L-Tube

Large Band Clamps (3), Beaded Connectors (2), Small Band Clamps (4), Mount Halves (4), Nylon Cable Ties (2 - not pictured)

Trimming the Main Body and L-Tube is much eaisier using one of the Small Clamps as a guide, the clamp can be lightly tighted to keep it from shifting

The J-Tube should be no closer than one inch from the front endcap of the silencer

Final assembly

Completed install

Careful attention needs to be paid to locating the Large Band Clamps and Mounting Halves. I personally had to do a fair amount of fiddling to get things just so, but once the initial fitting has been completed, the dB Snorkel can be removed and reinstalled fairly easily by releasing the large band clamps.

Let me state from the outset that I am no acoustical engineer and that I posses no special skills, tools or testing equipment. Once the dB Snorkel was installed, I wanted a way to quantitatively/objectively evaluate the effect of the snorkel had over my stock TurbineCore II silencer/spark arrestor without dropping cash for a high quality dB tester, or inviting a ticket from the city Noise Ordinance Officer by asking for this favor.

Unfortunately, I was not able to produce an eaisily quantifiable result under the circumstances, although I will try again soon. Check back!

Testing Equipment

• 2 sets of ears
• 1 laptop (recording device)
• 1 professional omnidirectional stand microphone (Electro-Voice Dynamic Model 630 An oldie but a goodie)

A very clear visual on how the exhaust pulse is distributed from the primary exhaust (lower) and the narrow secondary or peak pressure exhaust

Location & Conditions

Since sound radiates out in all directions from a source of noise, an enclosed space or a space with hard surfaces that could reflect sound were poor choices for this testing. Ideally, the perfect place would be exactly where you would ride a dirtbike, out in the open. Due to the fact that it was pouring rain, the test site had to be sheltered and ended up being in a grassy section of my yard with structures nearby. Oh well!

The microphone was located about 15 feet directly behind the motorcycle just under the porch roof. Because I was not using a directional microphone, and sound from the engine and expansion chamber was bouncing back from my house and garage I was unable to properly isolate the only normal source of focused sound - the exhaust.

The silencer has not recently been repacked since it is nearly new, I probably have about 15 hours on the current packing – FMF recommends repacking after 10 hours. The temperature was in the middle 50's with 100% humidity - dense air, also not ideal.

Despite my difficulties obtaining clear proof, the test still yielded some interesting results:

• Audio Sample Idle - Medium Rev - High Rev
  The above sample was taken from two separate samples and combined ? The first portion is the "stock" sound of my RM250 with the FMF TurbineCore II. ? The second portion is with the dB Snorkel installed over the TurbineCore II

  The character of the sound changed with the snorkel. The sharp edge to the sound was significantly mellowed, the "bark" for lack of a better word. If you listen to the brief wave file, you can hear the first test (without the snorkel) and second test (with the snorkel) - one right after the other. The tests themselves reveal this difference only with a good quality sound system at a higher volume (turn it up!), you'll know when it's loud enough if you can hear my 3 year old daughter's response to the first test – she started to cry.

   Bad Dad!
  

• Green indicates FMF silencer only Red indicates FMF with dB Snorkel Orange represents overlap between the two

  A review of the recording while using a graphical display of the audio frequency levels does

   

   not indicate a significant overall sound level difference at 15 feet, but does seem to indicate a frequency shift in the sample (see image right) from a peak in the higher frequencies to a fairly even split of high and low frequencies. The dB Snorkel seems to flatten out the sound and shift it to the midrange.
  
  Of course, this is all still fairly subjective since the tools I am
  using are hardly intended for that purpose.
  
  

• Audio Sample Idle - With and Without
  The above sample was taken with the dB Snorkel installed to the silencer, but with the main body loose so that it could be moved on and off the silencer fairly rapidly to show the contrast. All other testing was performed with the dB Snorkel secured, I suspect it is most effective that way.

  My wife, who was driving the laptop, couldn't really hear a significant difference other than a reduced "edge" to the sound (also my initial impression.) There was a significant amount of time between tests, so it was harder to pin down. From my location, it definitely seemed quieter to the ear – especially at lower RPMs where the secondary exhaust port was not in constant use.
  
  
• Overall performance of my RM250 did not seem to be affected; it pulled strongly through each of the runs I made on it with no noticeable soft spots in acceleration. It did seem to pull smoother off the bottom end with the Snorkel installed than without, but this is entirely due to my existing jetting vs. the less than optimal weather conditions. I suspect that some allowances will need to be made when jetting to allow for swapping the dB Snorkel on and off.

Other Observations:

• I suspect that too many of us are so used to riding with sound dampening already on our heads - helmets - that we are not noticing where the noise trouble spots really are. At close range – the FMF TurbineCore II already seemed quieter than the single-walled Suzuki expansion pipe. This should not have been a shock to me, as the first thing I noticed when changing over from my '90 RM 250 to the '98 was that the double-walled pipe on the '90 was

  significantly quieter at close range. The sound I hear when riding is from the engine and pipe, not the exhaust; the sound heard from any distance is probably from the exhaust. Still, I am hoping that Syd, or another enterprising individual may soon come up with a "wrap" that will address sound pollution transmitted through the walls of a noisy expansion pipe.
  
  

• A warning for members of the Short Inseam Club, like myself: I found that the dB Snorkel occasionally got in the way of the usual "swinging a leg over the bike." Anyone who has found themselves with a leg stuck up on the fender knows exactly how awkward this can be, however once you are aware of the issue it is easy to avoid and certainly easier than dealing with a fender bag.
  
  
• For some reason the dB Snorkel was extremely "fragrant" after testing, retaining the smell of exhaust for a full week after my last ride. This may be the nature of the beast, the Snorkel is certainly more ventilated than the rest of the exhaust system.
  

While it was difficult to quantify the results, my personal perception was that it helped. As my wife said, it "took the edge off" the higher frequencies, and that is the difference between just being loud and making you jump out of your skin.

Further testing under more controlled conditions would be necessary to give objective results. The following are changes I would make when I do this again:

• An inspection of the packing and possible repack of the silencer.
• Testing in an open area where sounds from the engine and expansion chamber will not reverberate.
• Testing with the clutch disengaged to remove as much mechanical noise from the test as possible.
• If possible, locate a resource that can perform an accurate 20" SAE J1287 test. I suspect that one of the local clubs that organize the Enduros or Hare Scrambles here in Colorado will have one for tech inspections at their events.

This is a thoughtfully designed, well-made product, and it is unique in the market at this time. The question: "Is it worth $85?" is one I am not really ready to ask, but if you are a conscientious, performance oriented individual the answer is pretty clear. I feel that it made a difference on my bike and I plan on using it.

dB Snorkel, LLC www.thedbsnorkel.com Post Office Box 54 Grand Blanc, MI 48480 Toll Free: 800-694-0287 info@thedbsnorkel.com