I was surprised to learn at Jennings GP this weekend that my Formula RD bike, ridden by Kevin Brown, was 2dB over the sound limit of 104. In the pits, it seems way quieter than a lot of stuff, including my CT175. But apparently not so when it's wide open on the track. The RD has an air filter (required) and similar sized silencers to what everyone else is running. I'll check the packing, but if that's not it, I guess longer cans are in order. My thanks to the Jennings GP management for letting us run it (and win )- we'll get it quieter next time.
Kevin was looking good. Pretty lackidasicle stop and go, but flying on the track. Made me want to ride f-rd again! Thats surprising that the bike was loud. The 175 sounded louder in the pits. When re-packing, I always use a layer of fiberglass mat, tie it off and then regular packing for the rest. Good luck!!
During and after this past weekend at JGP I heard a great deal of talk concerning mufflers and vintage race bikes. You four-strokers out there... to lower the noise level without affecting the power much you need to increase the "muffler" (megaphone or can) volume and then add a resonator!!!! Just adding a can from a modern sportbike won't necessarily work. Sure you can put a baffling device on a shortened set of TT pipes so that the resultant system has the same length as the original TT's but with this method you won't necessarily be at an acceptable noise level. Another thing... just because a lot of our bikes weren't raced with mufflers "in the day" doesn't mean they can't have a muffler and still be just as powerful (again.... read about "Brooklands cans" or the basic principles behind the VW bug "expansion chamber" muffler system and why they were used... even those cromags back then knew a little something about exhaust tuning... and that was during the 30's!). There is no logical reason why an old race bike can't be quieter. You may not like what would have to be done and how large the muffler may have to be but that's just the way it is. Some of you may think I'm fulla shit and don't know what I'm talking about since my bike obviously isn't the fastest XS650 out there so those of you who do, go to the next post, don't even consider pondering my advice. If you are open minded and really are interested in "food for thought", listen up and look around... take a peek at Eric's SRX. Also, take a look at modern mufflers, especially for big displacement twins... they aren't huge just to make them quieter... they need the volume to be quiet and still allow the motor to make power (remember? muffler volume>10 times the displacement of one cylinder?). Look at the size of the two TL1000 mufflers... look at the size of the can on a Yamaha (no comments from you about looking at "cans", triumphman ) Warrior. Huge ain't it? It's to subdue the noise yet still allow the motor to make power. Again... maybe I'm full of shit, but then maybe what I have to say is worth thinking about. I guess it's time for me to step off of my soapbox now...
It's the old iron triangle bit. You want a muffler to be small, quiet, and allow the bike to make max power. You get to pick any 2.
I almost wonder if they got the right pit, but the wrong bike. Having ridden both, I'm sure the 175 is louder. More rpm, plus wide-open piston port intake noise added to the exhaust noise. I'm gonna work on quieting both of them down.
Just don't take too close a peek If you had, you would have seen some of the ugliest welds and dents ever collected on an exhaust system. Went straight to VIR for a track Monday after Jennings, and had a friend ride the SRX so I could check the dBA at full throttle on the straight in much the same manner as reported on the Putnam thread (the bike had been right at the limit for Jennings tested statically at home, but was curious to see what trackside readings were like). http://forums.13x.com/showthread.php?s=&threadid=28865. It's baffling, but the single sounded much quieter to observers than SVs & Multis that were 1-2 dBA lower on my meter. A multi with a lower reading was literally painful to listen to when it passed, while the SRX sounded innocuous, but the fact that it can be heard farther away seems to be the problem for a big single at a track with residents nearby. We know that lower frequency sound waves travel farther than higher freq waves at equal volume, so the SRX could 'communicate' its location anywhere on the track, much the same as elephants do apparently dBA readings were similar to those reported by Jim Swartout using the same method, but unlike the static test described in the WERA rulebook (48",45', 1/2 redline) I don't know of a standard for trackside readings. Like Kawracer noted, angle of the meter is more critical than distance. Anybody know how these trackside readings are done?
Eric: Roger and I are new at this, therefore some testing will be required. It appears 45 degree angle was producing the highest decibel readings. We plan on several more extensive tests with our own bikes and other bikes, therefore will have additional information available. We are going to log temp, barometric pressure, humidity and cloud cover along with decibel levels to see if we can determine the weather's affect on levels. If your using a Radio Shack make sure it's on "A" weighting.
In Britain noise tests are always done in the paddock with the meter at the same position as described in the handbook for static tests. After being caught over the limit I insisted that the test was conducted again. I took the bike to a field at the back of the paddock and took off the fairing and a couple of brackets that rattled slightly, the upshot of this was that I was under the limit by a couple of decibels. The fairing was channelling engine noise to the back of the bike towards the meter and also all the other bits that rattled didn't help matters, I also hoped that the grass would absorb some of the noise rather than it be reflected back up off the tarmac. When the guy who was testing me asked why I did all that I told him that the test was for exhaust noise only! Another time when a friend of mine was 'pulled' I questioned the accuracy of the meter, at the time I was involved in the organisation of racing with another club and I had that organisations meter with me along with a calibration device. We chacked out both meters and found the one being used that day needed recalibrating, once this was done the bike was under the limit. Things are are lot more stringent in the UK than here and I've always tried to make sure my bikes are under the limit and overall I think it's a good rule to have, but there needs to be a hard and fast rule for us to go by. I like the trackside test because it gives a more realistic reading of the noise thats being generated but unless the meter is calibrated before every meeting and the angle/position/placement of it is exactly right we won't know if things are OK. Consistency is the key and the difficulty comes with finding the best place to test at each track. Well done to the Swartouts for the work they are putting into this.
When Harry Morse and I started doing the trackside testing some years back, we determined to use the following procedure. 1. Locate the meter in an area with an unobstructed line of sight. (I know, but it pays to mention the obvious sometimes.) Make sure that reflected sound will not color the readings. 2. Place the meter fifty feet from the edge of the track, at a height of about five feet. A camera tripod works well because it also helps isolate the meter from any mechanically transmitted noise. 3. We used a Radio Shack digital SPL meter set to 'A' weighting, 'Fast' display, and 'Max' reading. This gave us the truest readings Best of luck.
I lost 7hp trying to use a TL1000 M4 can on my SRX. Sold the M4 and went back to my reverse mega Jemco. Not saying that's the case with all bikes, just wanted to share my dyno confirmed info.
To Jim and all other fine folks working on this sound problem, I am making this offer. If you don't mind driving to Fort Wayne, IN, you may use my inertial dyno at no charge to check out various mufflers or rejetting needed for changing to a muffler. One stipulation is that the results with regard to changes in sound level and horsepower be posted here as well as sent to AHRMA. Obviously, the numbers obtained won't mean a whole lot in an absolute sense since the dyno is not calibrated and we don't have any special test cells for sound. However, the on the spot comparisons ought to be valid. Email me at [email protected] to make arrangements. I am also trying to make arrangements with AHRMA to set it up in the tech shed at Grattan. Anybody interested?
