# Muffler Mod?



## djblech (Jan 6, 2011)

I have read quite a number of articles where you guy's refer to muffler mods. At the risk of asking a question everyone knows the answer to except me, what is a muffler mod and where do you get them/it? Also, does the saw need to be adjusted after the install? I asked an old friend yesterday that does small engine work and he said something about turning the muffler around.
Thanks
Doug


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## RNLA (Jan 6, 2011)

Muffler mod is usually the process of opening or adding a port to the muffler. Some saws come with small holes and the saw can push more exhaust out if you open it up or add a second port. There is a fine line though, the engine needs a certain amount of back pressure, that is a whole other subject.


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## TreePointer (Jan 6, 2011)

And yes, you should re-tune your carburetor after opening your muffler.

Note that some saws respond better to muffler mods better than others, and the end result should also be a louder saw.


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## HittinSteel (Jan 6, 2011)

"turning the muffler around"   hahaha, that is a new one I will have to remember.

As mentioned above, a muffler mod is basically adding or increasing the exhaust exit hole of the muffler. This is done to create more power, through more flow and to also allow the saw to run cooler. The EPA has really choked up chainsaws and other OPE equipment, so it is a simple way to get that power back. A prime example of this is the Stihl 290/310/390 series of saws. They run okay stock, but become totally different saws with simple a simple muffler mod and a retune. Generally, the saw will need retuned because with the mod, the saw will turn more rpm's and may exceed the factory maximum unless richened.

Some drawbacks of a muffler mod will be increased noise/ fuel consumption and a voided warranty.


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## DanCorcoran (Jan 6, 2011)

Is this like removing the catalytic converter on your car (better performance, but exceeds EPA emission standards)?


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## HittinSteel (Jan 6, 2011)

DanCorcoran said:
			
		

> Is this like removing the catalytic converter on your car (better performance, but exceeds EPA emission standards)?



I'm not a car guy, but I would think it would be like adding headers and straight pipes


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## cygnus (Jan 6, 2011)

There are a few folks out there who can provide this service.  They have lots of experience and know what can be done with various saws.  I'd say to seek them out for all the details.  Try a site like www.arboristsite.com

...and make sure a spark arrestor is added to any new holes on the muffler.


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## wccountryboy (Jan 6, 2011)

I've got a follow up to the origional question:  As there seems to be little room for error, can somebody post pics of an MS 390 thats had this done?  I obviously don't want to ruin the saw, but would love to have the extra power.


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## smokinj (Jan 6, 2011)

Opening the muff up can be done many ways. All need retune afterwards.
http://web.archive.org/web/20051018212959/www.madsens1.com/sawtune.htm




here is mine on a 460 3/4 inch ss


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## CSAW (Jan 6, 2011)

While I realize there is something to be gained if done properly, I wonder how much extra noise is perceived as extra power.  Talking stock saw.


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## smokinj (Jan 6, 2011)

CSAW said:
			
		

> While I realize there is something to be gained if done properly, I wonder how much extra noise is perceived as extra power. Talking stock saw.



your going to get more noise for sure.....But it always comes down to air in air out....Muff modd. will get you about 10 percent not a huge difference.


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## HittinSteel (Jan 6, 2011)

wccountryboy said:
			
		

> I've got a follow up to the origional question:  As there seems to be little room for error, can somebody post pics of an MS 390 thats had this done?  I obviously don't want to ruin the saw, but would love to have the extra power.



This was an 039. I later sandwiched a screen in there. A hole the size of nickel would be a pretty good guide. If you want to get technical, you can measure the exhaust port on the cylinder then do not open the muffler more than 125% of that number. I think my mod in the picture was rather conservative and still totally changed the attitude and power of the saw.


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## DanCorcoran (Jan 6, 2011)

If it improves performance, why don't they just manufacture them that way?  Are the mfrs deliberately de-tuning them?


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## smokinj (Jan 6, 2011)

DanCorcoran said:
			
		

> If it improves performance, why don't they just manufacture them that way?  Are the mfrs deliberately de-tuning them?



quick answer yes.....Epa reg's....But you fire up an 880 and it  seems to be breathing quite well! lol


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## Highbeam (Jan 6, 2011)

The stihls are already very loud. I don't want the noise so I run a stock muffler.


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## smokinj (Jan 6, 2011)

Highbeam said:
			
		

> The stihls are already very loud. I don't want the noise so I run a stock muffler.



You would hate the dolmars then...Stock 7900 (atleast on a couple year old one) Is very loud.


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## HittinSteel (Jan 6, 2011)

Highbeam said:
			
		

> The stihls are already very loud. I don't want the noise so I run a stock muffler.



Are you serious? My neighbor was cutting with his 290 the other day and I couldn't even hear the saw until he was at max throttle then it was just a high pitched whine.


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## CSAW (Jan 6, 2011)

smokinjay said:
			
		

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My 420 is quite quiet I think, (guess the cat helps with that).  That's why I don't want to mod it.  I imagine those bigger boys like the 7900 are a different story.


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## smokinj (Jan 6, 2011)

HittinSteel said:
			
		

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I think the 361 sounds like that but spools up real fast and holds that pitch very well...But drives me crazy listening to it.


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## HittinSteel (Jan 6, 2011)

smokinjay said:
			
		

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Yes it does...... also very choked up exhaust port for EPA reasons. Another saw that really benefits from a muffler mod.


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## Highbeam (Jan 7, 2011)

Coming from a poulan wild thing, yes, the stock 290 is very loud. You could cut without ear protection using the little poulan. I am sure this is a relative thing but I don't saw logs using the stihl without hearing protection, most I will do is start it up and test run it after a good cleaning. No loaded cutting.


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## southbound (Jan 7, 2011)

This is how I do my 290's...

http://www.arboristsite.com/chainsaw/72542.htm

They are little rippers now lol...........


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## HeatsTwice (Jan 8, 2011)

CSAW said:
			
		

> I wonder how much extra noise is perceived as extra power.  Talking stock saw.



While I know this is not a "Disney" site, but proper safty apparel includes ear protection. I don't leave home without it (too many rock and roll bands in my youth).


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## HeatsTwice (Jan 8, 2011)

duplicat deleted


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## southbound (Jan 8, 2011)

I went to a friends house today to buck up a tree the local power co cut down for him..After the chaps I put on my hardhat cause my ear plugs are kinda attached and I like earplugs..  Well they all laughed at me, but I gots lots of wood!


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## CTYank (Jan 8, 2011)

smokinjay said:
			
		

> DanCorcoran said:
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2-strokes are very visible targets to EPA, CARB etc., because of their innate propensity to spew unburnt fuel out the exhaust. Leading to current catalytic converters and stratified scavenging. It boils down to two facts:
1) Exhaust is propelled through opening port by gas pressure, with high velocity and were there nothing in its way, would happily draw mixture coming from transfers along with it. Typically there is waste of fuel (about 33%) and lots of HC in exhaust.
2) Positive pressure reflected wave can cause some of this mixture to return to the cyl. This is how expansion-chambers work; they're BIG.

With the short length of most mufflers, there's a problem enabling the return pulse, so some limiting of freedom of exhaust can reduce these emissions.

With stratified-scavenging/charge, the "mixture" that's drawn out the exhaust is air, not fuel & air. Much cleaner exhaust, reduced emissions, reduced deafness.

A lot of this muffler-modding reminds me of kids back in the day with their glasspack mufflers; noise IS power.

It's not a bureaucratic exercise. Some mfgs have been unable to comply, and closed shop. 2-stroke road bikes are gone for some time now, too.


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## smokinj (Jan 8, 2011)

CTYank said:
			
		

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Some model where just choke down to pass epa with nothing else done to it so those are the one that really shine. Not enough 880's sold so there not all over that model like the 361,362,441,391. And A lot more.


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## Kenster (Jan 8, 2011)

I have an MS390 that I bought new with a muffler mod.  I run a 16 inch bar on it because that takes care of all my needs.   This saw, with that short bar, rips through all my wood.  I only cut hickory and oak.   It's loud.  I use ear plugs most of the time.


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## Mcbride (Jan 8, 2011)

I wish people would not mod exhaust systems for more noise.
Regardless if its a car, bike, or chainsaw, they should be made even quieter if anything, not louder.


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## smokinj (Jan 8, 2011)

Mcbride said:
			
		

> I wish people would not mod exhaust systems for more noise.
> Regardless if its a car, bike, or chainsaw, they should be made even quieter if anything, not louder.



yea I bet that 390xp just prrrr's like a little kitten! lol my 880 sounds just like an old yz 125.


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## TreePointer (Jan 8, 2011)

I agreee--modding for the sake of more noise moronic.

However, the Stihl 290/310/390 series respond well to a muff mod.


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## southbound (Jan 8, 2011)

My 046 with the dp cover runs stronger... Most saws will gain from a mm....


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