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PostPosted: June 25, 2008, 8:06 pm 
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Joined: July 17, 2006, 3:09 pm
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Location: Holly, MI
Be careful about relying on turning the tips away from the meter. I ran at Calabogie last year. They have a nasty habit of hiding on the track while taking measurements. I don't think you can count on them being in the same location all the time.

By the way, re-read their rules for the screening test. It says the measurement is with the engine at "redline". Get creative if you know what I mean. :D The track doesn't care how much noise you make. They have to measure because the neighbors complain sometimes.

Good luck.
Ken


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PostPosted: June 25, 2008, 8:46 pm 
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Since this thread is back, track noise limits (which are only going to get more restrictive) are one reason why my next car is going to be turbo. The turbo does a great job of quieting things down, and between that and a small muffler I should be good at any track.

I heard somewhere that the recent turbo Neon doesn't even have mufflers due to the turbo doing so much of the work, just a cat and resonator.

Oh, and the opposite is true, too; because of the noise limits I did not want to go with a high-compression, high-rpm, normally-aspirated engine. The way they make power is lots of rpm and lots of noise due to the high-compression. No thanks.

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PostPosted: June 25, 2008, 8:50 pm 
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BB69 wrote:
Be careful about relying on turning the tips away from the meter. I ran at Calabogie last year. They have a nasty habit of hiding on the track while taking measurements. I don't think you can count on them being in the same location all the time.

By the way, re-read their rules for the screening test. It says the measurement is with the engine at "redline". Get creative if you know what I mean. :D The track doesn't care how much noise you make. They have to measure because the neighbors complain sometimes.

Good luck.
Ken


If you point the exhaust away from the meter, wherever it is, some poeple get really upset, saying you're going to shut down the track due to cheating the rules. As one time I was the recipient of said anger... I can understand their point.

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PostPosted: June 25, 2008, 9:11 pm 
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I've never heard that one. At the SCCA events I've attended at Mid Ohio Sports car complex and CMP they tell you what turn the meter will be in and what side of the track so you can divert your exhaust etc. I guess it's like anything else, things are different all over. All situations and circumstances are unique.

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PostPosted: June 25, 2008, 9:39 pm 
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What these people are saying is that the neighborhood forced the track into doing the noise limits. If everyone specifically points their exhaust away from the meter, noise that would have been flagged simply heads off to a different neighborhood. What will happen is that the neighbors will either get the noise limit tightened further, or, once it reaches critical mass, the entire community will get the track shut down.

They do have a point.

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PostPosted: June 25, 2008, 10:43 pm 
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KB58 wrote:
What these people are saying is that the neighborhood forced the track into doing the noise limits. If everyone specifically points their exhaust away from the meter, noise that would have been flagged simply heads off to a different neighborhood. What will happen is that the neighbors will either get the noise limit tightened further, or, once it reaches critical mass, the entire community will get the track shut down.

They do have a point.



Yeah, I got it the first time you said it. I was only telling you what happens at other tracks with other organizations. At tracks where the meter is always at the same place, it is likely located opposite the direction of the complaining community/landowners. They don't care where the noise goes as long as they minimize it in that particular direction. Tracks that are surrounded by development are obviously a different animal, hence my comment that things are different everywhere.

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PostPosted: June 26, 2008, 6:50 am 
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The worst part about this, is that Calabogie is in the middle of nowhere. It was built on 5000 acres of woodlands. The little village closest to the track says the noise carries from the cars. Of course, this is a huge snowmobile area. You know that the sleds are running at all hours of the night through the woods. The track only runs from 9AM-5PM. It's frsutrating to say the least.

We ran at Waterford here in Michigan last Friday. That track has been around for 50 years. The people that built their houses right next to the track are now complaining about noise. The track has a very strict sound level, and it's not uncommon to see cars with dual exhaust capped by Supertrapps on both and both tips turned away from the meter. We weren't allowed to start running until 10:30AM and couldn't use the PA system becaue of noise. The skeet shooting range on the same property though was up and running by 10AM blasting away. :roll:

Enjoy your time at Calabogie. That is far and away the nicest track I have ever been to. Get to know the people running it, and they can help you with the noise issue.

Ken


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PostPosted: June 26, 2008, 7:50 am 
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Has anyone bought those chromed side pipes? They don't describe the actual diameter... or is the actual muffler 3"? If I could find something like that in 2.25, I'd like one if someone else wanted a second one.


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PostPosted: June 26, 2008, 2:14 pm 
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On the note of track noise, it is somewhat surprising how far the sound of the "louder" cars on a track will travel.

While it's not the same application, I have heard a number of V8 muscle car guys claiming that for a straight cylindrical muffler the Moroso Spiral Flow and Flo-Pro Twister are quieter than other similar shaped "bullet" or glasspack mufflers like those offered by Dynomax of Magnaflow. Not that any of the smaller bodied cylindrical mufflers attenuate sound all that well, but I'm very curious to try one of these first hand eventually. In my opinion these work on more "sound" engineering principles than I see on that DNA muffler...But you never know until you try one.

One thing I've also used to reduce noise coming out of a muffler measured at ground level, is to actually turn the tip(s) straight up, rather than down to the ground or to one side where some of it would still reflect off the track wall back towards sound control. That way rather than the sound being reflected significantly in two dimensional space across the ground plane, a large portion of it is shot straight up and dispersed more into a three dimensional volume. However this runs into some issues on the low side of a car as the cars body still reflects a good portion of the sound outwards along the ground plane. Ideally you would want to get the opening higher up to be able to disperse freely around an unobstructed hemisphere. In theory the extra height of the tip would even act as a 1/4 wave resonator to cancel a little additional sound at certain frequencies. Although you probably don't want to take it to quite this extreme...

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PostPosted: June 26, 2008, 5:19 pm 
Never underestimate the power of complaints to local politicians - our track, which was around since the 1940's, got shut down for good because of noise, even though it was out in the boonies. Developers bought the land around it, built houses right next to it, and even though we had been enforcing full street exhausts required on all cars to prevent it, a couple of complaints were all that was required to shut it down. Ditto for the police pistol range across the road from it.

I'm guessing that voting racers come and go, but voting residents are there to stay, as far as the local politicians are concerned.

As ridiculous as it may be, people in Vancouver BC who built right under the final approach to the Vancouver International Airport (a huge, busy facility) tried to get the airport closed to stop noise. There weren't successful, but they did manage to force all flights to change their final approach paths, except in life-or-death emergencies!

IMHO, if there's even a hint of complaints, you've got trouble, so I think we need to be very careful with our noise output... :oops:


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PostPosted: June 26, 2008, 6:48 pm 
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Sounds like we need some plans for a good locost muffler. Considering the success shown in some of the motorcycle engines, I no longer believe it's required to be load to get power.

You can sit next to motorcycles in traffic that make almost no noise and those engines are at a very high state of tune. The motorcycles also do not have the luxury of much room for the exhaust system.

I don't know how they do it, perhaps someone wouldn't mine sawing up their system and posting the pictures? :) I am surprised at how small the outlets on these exhausts are, so just a little back pressure may be helping.

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PostPosted: June 27, 2008, 9:45 am 
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The Honda CBR 600 F4i muffler definitely flows well considering its design, and is reasonably quiet. It's a multi chamber muffler much like an ordinary automotive muffler, just smaller. I'll describe it as best I remember...Unfortunately I didn't have the forethought to take pictures during that part of the development. I believe it had three chambers, we'll call them 1, 2, and 3 in the order from the front of the muffler to the back of the muffler. The exhaust enters into into chamber 1 hits a heavily perforated plate that bisects the chamber. The open area of the perfortaed plate significantly exceeded that of the exhaust tubing, thus minimizing losses but creating a more even/consistent air velocity. It then flowed into a tube that carried it to the chamber 3, then the next tube carried it back to chamber 2, and finally from chamber two it hopps into the last tube that goes through chamber three and out the rear of the muffler. All tubes inside the muffler had bellmouth ends, and were extended from the dividing wall a distance into the chamber for tuning purposes. The main can was of double wall construction that had a dense layer of insulation between the inner wall and outer wall. I don't recall for certain but I believe the inner wall was also perforated.

For cost, weight, and packaging reasons we decided to replace it with a muffler of our own construction. After a not insignificant amount of development (at least 17 iterations) it finally achieved the same dB level, but was likely down a little on power compared to the stock Honda based on pressure drop tests. It was based on two extended inlet/outlet expansion chambers placed in series. It had a straight through flow path, significantly smaller in diameter than the stock Honda, but required the use of smaller tubing. It also still required a perforated plate/cone much like the stock honda muffler used. In the end it was able to get a 600cc sportbike motor at 11,000rpm to under 110dB measured about 20 inches from the outlet. After extending the exhaust (which was already pointed vertically) to get the exit above parts of the car it was reflecting on, I think our final number was 108dB.

The problem with mufflers is that the primary ways to really get them quiet tend to go against ways to get more airflow and tighter packaging. Basically a smaller inlet is better. A larger body is better. The larger the inlet, the larger the body must be to achieve the same sound damping. Not that there aren't other tuning means that allow one to get more or less sound damping for a given airflow need, but astraight through 4" OD cylindrical muffler with a 2.5" inlet/outlet will not be as quiet as a similarly designed straight through 6" OD cylindrical muffler with a 2.5" inlet/outlet. Thus why external side pipes that look good (not much larger than the inlet/outlet tubes) are going to generally be significantly louder than the really dorky looking solutions, without necessarily performing any better.

The development of a muffler that is functional, cheap, and attractive for the average locost builder to make in his garage would take a considerable amount of time and effort, and would likely end up not working any better than many of the relatively affordable commercially available products already used. You'd basically be reinventing the wheel to save a few bucks. The other option would be to find an existing muffler that works reasonably well and uses simple construction, and "reverse engineer" it (aka steal the design) to be independently reproduced. If the spiral muffler baffle design were to work well enough, it would probably be one of the better candidates for a locost muffler.

On the other hand, I've often wondered how that same basic exhaust I built would sound if were not so limited in packaging constraints (make it bigger) and run on a normal car engine (not on a high compression, agressively tuned, engine at 11,000 rpm).

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Last edited by Driven5 on June 27, 2008, 10:08 am, edited 2 times in total.

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PostPosted: June 27, 2008, 10:02 am 
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horizenjob wrote:
You can sit next to motorcycles in traffic that make almost no noise and those engines are at a very high state of tune.

Idle is completely different from driving at speed. When I ran my Honda engine with a straight pipe, it idled incredibly quiet.

FWIW, at bike trackday events, some sportbike riders at Laguna Seca have trouble getting under the 92dB limit using stock exhaust!.

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PostPosted: June 27, 2008, 2:25 pm 
There are lots of Yamaha R1 bikes in my area, and they seem to be eerily quiet, even gong by at close to 14,000 RPM. They have a single Titanium muffler as stock equipment, so that's what we're using on our Zetec Locosts. Of course, we haven't heard them yet, but my reasoning (probably flawed, but...) is this -

The R1 is a 1-liter engine, putting out 170-180 hp @ just under 14,000 rpm, versus my 2-liter engine, which will be putting out a little less hp, at less than 1/2 the rpm. So, basically, both engines will have essentially the same flow rate of gases at maximum output. Now, I know that there's a difference between muffling a 14,000 rpm engine and a 7,000 rpm one, but it's my impression (and others ^ seem to agree) that the high-pitched screaming exhaust sounds are tougher to attenuate than the lower pitched ones. So, I'm expecting this muffler to work quite well with the lower-pitched, lower-rpm exhaust note of my Zetec engine. It's also made entirely of stainless steel and titanium (so, no corrosion, and no packing to burn out), and is heat-shielded, so you won't burn yourself on it. It's 2 1/2" in, 2 1/2" out, by the way, and has a built-in stainless bracket and hanger for mounting. Seems close to ideal to me....

Your thoughts?


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PostPosted: June 27, 2008, 3:56 pm 
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zetec7 wrote:
Your thoughts?
While the R1 muffler was likely tuned for a given range of frequencies emitted by a it's high revving motor at various rpms, I don't know what that is or how it might relate to use on an automotive engine, and if you do a Google search you'll see that there are people out there that have done this before...So it can't hurt to try.

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