Tips on how to reduce the racket your bike makes

[211kawasaki]

Welcome to the new noise debate - a positive attempt to ditch the bullshit and get on with it.

Tip # 1
The best start point on the path to reduce noise if to get a muffler, if your bike dosnt have one then it needs one. Even my AJS now sports a huge big chrome thing that looks like it should be there and drops a truck load off the DB.

Fatboy - its your domain, what about some wisdom.

211

[oldfart]

Spent most of the weekend fabricating a new exhausts system. Parts required to build muffler ( $25-00) shown

[pokey]

what are you using for the baffle stew? it dont seem to have many holes/inch


 anyone know a place to get rubber blocks for cylinder fins?

 

[Lozza]

Old inner tubes pokey.That core looks like it will need a few more 'oles Stew
Another one is a core where the 2 ends a inserted diagonaly into the end can and the ends are past each other in a central chamber.I know I didn't explain that well but I'll get a better pic of it.

[Tim754]

Multi cylinder four stroke sidecar Easy!!!! Headers into 4in1 collector, then into car type small muffler/resonator, then short droopy tail piece directed at ground.  Make sure your have some sort of heat guard over hot bits for the passenger/swinger/monkey/fat ballast protection. Might be an idea to check your jetting after finishing noise abatement project too. Tim

[vandy010]

with 2 strokes, it all seems to be relative to the silencer.
i'd imagine a few of us will travel down the path of making our own, cause thats what we do.
is there any formula/theories in reguards to core diameter/length of silencer for size of engine?
keeping it simple for 2 strokes with this question.

[fatboyracing]

Hi all,
I agree with Dave lets just get on with it,
firstly even if your muffler is brand new pull it apart see how it is packed in my experiance mufflers staight from the factory are packet badly usely way too tight,I had bad noise problems with brand new pro circuit mufflers which went 106db on a modern KX85 the owner was going to send it back as the pipe and muffler cost $1200.00 each he had two bukes,but on closer examinatin we pulled it apart and it might not have been packed as the packing had been jambed in way too tight, we repacked it with some wool packing, not too tight or all the noise goes straight out the back not through the packing ,result 97.9 db which is a pass.
Second check your perfeated tube and drill out your holes as big as possible, uselly when they are new they are about one eighth, drill them out to about a quarter as big as you can do every hole repack again and you will notice the difference even on an old muffler.
If you are making a new muffler make it as big as you can, uselly two stroke mufflers are two short, most of the muffler is in behind the side panel and you dont even see it anyway The longer you make it the quieter it will be if you follow steps one and two as well.
four stroke bikes are the same except you can gain even more as much as 5 db by rapping the outside of the pipe with a suitable thermal rap,this is the cheapest and easiest way of making a four stroke queit.
I got my old XL350 from 114db down to 98.9 by doing every thing I listed above drill tube,repacking and rapping the pipe. Cost $80.00 and a bit of time it is really that easy.

Cheers
Fatboy

[mainline]

my bits...

old grease gun case with thread cut off, piece of tubing from bench press accessory that I didn't want, couple of bits of sheetmetal hammered into cone shapes, and perforated sheet from old tv table rolled around a broom handle and welded up.

[mboddy]

Long aluminium silencers are better than steel or carbon fibre.
The stinger can be extended back into the body of the 2stroke expansion chamber.
Supertrap silencer rings can be added to the end of the alloy silencer to take the bite out of the sound.
Rubber plugs between the cylinder and head fins can take out the ringing.
Countershaft sprockets with the rubber lips to cushion the chain can reduce chain noise.
Thick rubber blocks inside the countershaft sprocket cover.

Can we wrap the exhaust pipe in something?
Should we be getting GMC to make us thicker walled pipes?

What other suggestions do you guys have? 

The stinger before the muffler can be extended back into the body.
This has been used successfully in the past on bikes like the TZ750.
My TDR comes from the factory like this.
It does not reduce the power output but it does reduce the noise a lot.

For more detail see '10.16 Tailpipes' in 'The High-Performance Two-Stroke Engine' by Dr John C. Dixon. Haynes 2005.

Here are my suggestions from the Decibels thread.

I highly recommend Dixon's book.

[211kawasaki]

Sensational advice,

Fatboy, do we argue for the RPM limits as shown in the GCRs generally which will allow the reading to be at a lower RPM in vintage MX. For example 54mm bore TM125 will be 800 or so RPM less on this scale than the MX scale as used today. In effect you can have a louder TM125 if you race DT than MX if you go by the current situation. (yes folks there are different scales of measure but you will have to know bore and stroke).I suggest that the commission lobby on behalf of the riders to have the scale as used by Speedway, Trials, Dirt Track, Road Race etc etc etc and not be lobbed in with the same soup as modern MX.

I feel that its important that there be ways for the riders to reduce the noise of the bikes and I also feel that there is a responsibility of the commission to look for ways within the rule book that we can make the rule book work better for the VMX community.

We need to determine the basis for which modern MX made the RPM limit to DB, Modern MX bikes are very different to VMX and what they use to make their determination of RPM will not be a suitable rationale for VMX plain and simple. How did the Modern MX guys come up with their scale?

What do you think?

[gorby]

Its worth a try to have vmx classed with the others and not with the moderns and the other suggestions
are helpful except that the rubber on the sprocket covers and on the sprockets would only help if the noise testing is done by the drive past method(ADR style).
Another source of noise is the induction into the engine,the quieter the muffler,the more this comes into play.



this s/hand muffler from a 2001 YZ250F cost me $60 (was dented on inside) and the noise level tested at 99db,this could be reduced by replacing the packing,fitting supertrapp style end plates and or wrapping the header.
its appearance could be toned down by painting it flat black.

[Freakshow]

IM curiuos to know if you put a pipe away from the motor to a  farther point ( some kind of hooked up pipe section, what  the actual noise of the motor contributes to a readiing on a meter at the perscribed distanc and position.   SO like the exhuats exist from the front away from the bike and meter, but the meter is still in the same position and reads of the other background noise from the bike, id be curious as to how much impact or contribution to the final reading is actually made by things other than that exisiting out from the end pipe.

[fatboyracing]

Great idea Dave I think we should argue for the RPM limits as shown in the GCRs generally which will allow the reading to be at a lower RPM in vintage MX. The biggest advantage would be for big bore bikes but I think all bikes would be at a lower RPM, I did test a couple of bikes at Classic Dirt using this scale and it did make a bit of difference. This would work great as long as all riders new there bore size and I think that most riders know what size there piston is, the table in the GCRs is very easy to understand.
Please let us know what you think as Myself and Dave would be more than happy to lobby MA for us to use this scale instead of the modern MX RPM scale.
We as commissiners are here to work for you and I think this would be a much fairer way of measuring VMX bikes.

Cheers
FATBOY

[Freakshow]

What about the 2 strokes ?  mine seems to lighten off the cackle the higher it revs ? low down it sounds like a 4 stroker

im thinking a low rev would give my 2 smoker a worse reading ?  then again i have no idea what its pumping now and wheather the meter hates the low gurgle or the higher crackle.  still to my ear is sounds quieter the higher it revs 

[husky61]

Tip of the day.

Mnaufacture or purchase a suitable silencer.

To easy

Time to move on now