Sound

Randy Tallon · Joined: 02 Jun 2007 Posts: 6

Hey, I'm a newbie to this all (only about 6 autox on the kart), and at the last event I started violating sound, not by much, around a decibel to a decibel and a half. So I'm getting an airbox, but am still kinda nervous because the next event is at a site which is notorious for sound violations, everyone seems to pickup almost ten db at that site versus others, just because of the acoustics (its basically in a canyon of condos and concrete retaining walls). So how much a reduction in sound can I expect? Also what other things can I do to get my sound levels down. Just for reference, our sound regs are 93 db or higher and your run gets DNF'd, not cool when on your fastest run by half a second you get dnf'd because you got a little louder. And finally, I've been told that putting an airbox on will require different jetting otherwise itll run to rich, can anyone give me an approximate change in jetting sizes for a starting point, since its iffy if I'll get a chance to go test with the new airbox before the next event. Thanks for any and all advice you guys can give me.

Larry MacLeod · Posted: Sun Jun 03, 2007 5:57 am Post subject:

Depending on where the sound meter is, you might help the situation by adding a small sound deflector to the end of your silencer. Maybe just pointing it into the ground might be enough. Or if the meter is in a particular place along the property line, you could point the deflector away from the meter at the nearest point.

AN airbox *might* help, but I wouldn't guarantee anything. You could also try a different silencer (longer one with fresh packing).

Good luck. Definitely let us know if you're able to make it comply.

LM
_________________
F125 #196
Old Birel/ hodgepodge Honda CR125
Lefty Funk
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Michael Contour · Posted: Sun Jun 03, 2007 10:04 am Post subject:

In San Diego, we have a 93dB max limit as well, measured at 50 feet from the course in an area where the vehicle will be under accelleration. While it is not a hard rule here, we all run air boxes, and most of us run the Moran silencer as well. The loudest I have ever come in at is 91 dB.

Michael

Larry Andrews · Posted: Mon Jun 04, 2007 12:31 pm Post subject:

A couple tips...

-Airbox is almost always worth a dB or two.
-Silencer makes a big difference, output direction is worth a bit.
-A huge amount of the noise emanates directly from the expansion chamber. A one layer-thick wrap with a heavy fiberglass cloth layer will often damp the sound by 3-5 dB.

Virtually anything that changes the noise level will also change your jetting. Be careful...

hth, la

(oh yeah - Eric N and I got popped at the SD event a few years back and tried using dryer duct to put the sound right on the ground. it might have helped, but both of us were lifting near the sound meter also so it's hard to know. that setup did look pretty darned ridiculous though. Smile

Randy Tallon · Joined: 02 Jun 2007 Posts: 6

Well between a combination of the airbox, repacking the silencer, and being at less rpm's at the sound meter my sound dropped from a 94 db peak at the last event to an 86 db peak. So I think I have enough of a margin to be comfortable with now. However, one of the other karters there this weekend was saying that he needs to repack his silencer about every 6 events to stay under sound, does this seem right? Or should it last longer than that?
-Randy