Guys,

I am doing a track day next week and the noise limit is 101db. Currently I my bike has been measured at anything between 101 - 104db depends on where and who does the testing.

I need to get it down a bit to be on the safe side and was wondering what you guys think will be best method.

Currently the bike has Jolly Moto pipes with carbon cans of unknown origin. PJ38s and open airbox.

Should I just fit some different silencers, standard MC21 or newer race ones. Will pod filters reduce any of the induction noise?

What are most of you other guys noise tested at and whats a rough setup?

Cheers

I dont think the induction noise should make a difference mate. If they test it as per ACU rules (depends on the track, MSV tracks do) then all they'll get is exhaust noise.

I would recommend you take some standard end cans with you, but let them test the bike as it is first. If it fails put the standard cans on and try again. Once you've got the sticker put your normal ones back on and hope they dont pull you in for another test! I've never seen them retest bikes once they have already done them.

Thats was pretty much my thinking. Was also wondering what sort of noise levels most people make with what set up.

I may put the standard ones on first, just to make sure it passes, if it fails, then passes, then get loud again it may attract a bit more attention. .

The track I am doing is Brands GP circuit so would imagine everything is done properly....anyone know how to make the rev counter appear 2000rpm higher than it really is .

It's almost certainly the PJ38's I reckon, plus the silencers can probably do with re-packing. I think Cartman fibre cans also often tend to be just a little louder too... they certainly seem to have a different sound, to my ear. (Who said that?!)

Although as chappyr1 says, the measurment shouldn't be effected by the carbs, but it depends if the guy with the equipment knows how to use it properly, plus the microphone on the tester as far as I know isn't directional so I would try some pods on the carbs and repack the cans. Pods will alter the jetting a little.

UNI Filters

I'm looking at part number UP6245ST (2 1/2" x 4" x 6"), or 62mm x 100mm x 150mm for those of us in the real world, for mine if I can actually find a supplier! Just a shame they're a rather garish red -- typical MX!
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Andy.
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Your right about them needing re packing, my titanium JHA ones on my road bike are very quiet, but to be honest I dont want to risk them now JHA are out of business and I wont be able to replace them.

Pods look like a good option,

Yeah, I say it because there are plenty of NSR's out there with race pipes and (drilled) airboxes that are extremely quiet in my opinion... especially when put next to mine with race pipes and pods. Pods or open carbs make one hell of a difference.
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Andy.
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Just listening to Tom's RS250 fire up at Beaulieu on open carbs, I'll second that Andy Awesome sounding induction roar, Audio Heaven!! I'd love to run my NSR sans airbox, need a Jet Kit though
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Rich
MC21 Track Bike / RS250 NF5 'Spencer', NX5 'Cadalora' & NXA 'Aoyama' / RS500 / Two Brothers Racing RC30

For info, my MC21 with Tyga mild steel pipes and carbon cans made 105dB every time. Right on the limit for race cans.
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Now that's interesting, my '28, open (32mm) carbs, Tyga pipes, unknown race cans, 99db at Cadwell yesterday.

94db with the airbox.

Both measured by the same guy in the same manner, i.e. as the ACU say.

Also be aware, not sure about anywhere else but Donington have drive by db sensors around the track, their point of view is sod what the ACU say, the council say the noise limit is the limit, not the limit at 7000rpm measured at the pipe and it's the council who set this stuff.
I got thown off a quiet day running stock pipes.
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My 18 read 104 with drilled box and standard pipes. The 21 avoided noise testing by not being used in the 1st 2 sessions.

Leigh if it's the normal brands guy he let me sneak about 1000rpm under last time as it was at the limit already... Must have a soft spot for real bikes...! But I don't think you'll hit 101 as it is!
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NSR300R - Why did i ever have a 250...

fontyyy wrote:
Now that's interesting, my '28, open (32mm) carbs, Tyga pipes, unknown race cans, 99db at Cadwell yesterday.

94db with the airbox.

Both measured by the same guy in the same manner, i.e. as the ACU say.

Fontyyy, both Steve and I have a curiosity regarding your cans! Your '28 certainly seems to work rather well (when it has good pistons/rings!), but the cans look restrictive. We are both convinced that they are holding the motor back slighly, even if it's only a couple hundred RPM and 1/2hp. A restriction is a restriction however, and a restriction in the cans will almost certainly make them quieter.
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Andy.
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Luckily its a 101db day not a quiet 98db day then (from memeory when I used to do sound testing, 3 db is twice as loud) so I am in with a chance. Maybe disconnect the rev counter and claim its doing lots of RPM...lol

I will take standard cans with me for worse case scenario, also got some almost new carbon fibre cans which I will try this weekend, if not I could also risk my almost new titanium JHA cans.....failing that....cry!

Or make some blanks from a coke can to fit at the pipe / can joint. Small hole in the middle which allows enough smoke through for the motor to run, but makes it whisper quiet. Once tested, remove.
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Last edited by Dave Ett on Wed Aug 13, 2008 9:51 am; edited 1 time in total

I wonder what the old 60's/70's strokers sounded like with no silencing... Anyone on here 'wisened' enough to have heard them??
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NSR300R - Why did i ever have a 250...