# Stihl MS 391 Muffler Mod



## Austinace (Sep 16, 2010)

I have the MS 391 and it not quite broken in yet. I am looking to get more power out of the saw after it is fully broken in. And i am leaning towards a muffler mod. I was looking for some assistance or some advice or instructions to do so. And would it really be worth doing and make a noticable difference or not. Thanks for all the help ahead of time!


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## Mac B. (Sep 16, 2010)

Do a search. There are tons of 361 muffler mod threads. I think one is in the sticky section. Oh and by the way it is worth the time to do one. Welcome to chainsaw Heaven.

Mac


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## Bowtie (Sep 16, 2010)

He is talking bout the MS391, not the 361, totally different animals.


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## Austinace (Sep 16, 2010)

Yea im working with the 391, and i have been told that the 391 doesnt make the power that a 390 makes when both having muffler mods because of something new the have done with the 391.


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## Bowtie (Sep 16, 2010)

The 391 is a strato saw, like all will be before too long. I dont know of anyone that has modded the 311/391 mufflers yet, but Im sure it can be done, just a new science at this point.


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## 2000ssm6 (Sep 16, 2010)

Give her a few more tanks of fuel before the mod. After the mod, unless you have a spare stock muffler, the dealer will know its been tampered with. He could deny warranty. You might be the first to mod a 391 muffler but I'm sure it will gain some power. Can't say how much.

I'd do a "Lake 361 style" pipe out the recoil side. Looking at the IPL, the 391's muffler looks just like a 441.

From what I've read here, a 391 will wipe the floor with a 390.


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## Austinace (Sep 16, 2010)

Well thats good to know. The plan is to order another stock muffler and mod that one. keep the muffler that is on it now for the untampered one so if i ever have to take it back in to the dealer it looks to be used as well as stock. But at the same time i dont know if i want to be the first one to mod that saw, my luck instant blow up. I was hoping to get a picture of one that was already modded and maybe some detail on the performance vs a stock 391.


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## 2000ssm6 (Sep 16, 2010)

Just search on carb tuning, once you get the idea, it should not "blow up". Can you post of a few pics of the muffler on the saw?. I could use MS paint and add a circle where I'd put a pipe.


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## COLD_IRON (Sep 16, 2010)

I'd let the warranty lapse before modding the saw, just my 2 cents.


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## Anthony_Va. (Sep 16, 2010)

Austinace said:


> Yea im working with the 391, and i have been told that the 391 doesnt make the power that a 390 makes when both having muffler mods because of something new the have done with the 391.



I don'y buy that. They are probably even more choked up than the 390 was.

I hear they are harder to find gains through porting work.


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## Farmertim (Sep 17, 2010)

I always thought that the strato saws had less choked up mufflers because the decrease in emissions is gained through a different engine design rather than restrictive mufflers--unless I have been misreading information here on AS.
Tim


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## BloodOnTheIce (Sep 17, 2010)

2000ssm6 said:


> From what I've read here, a 391 will wipe the floor with a 390.



very true.


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## Anthony_Va. (Sep 17, 2010)

Farmertim said:


> I always thought that the strato saws had less choked up mufflers because the decrease in emissions is gained through a different engine design rather than restrictive mufflers--unless I have been misreading information here on AS.
> Tim



Makes sense enough.


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## Austinace (Sep 17, 2010)

So what should i do fellas? Will it have more power than the 390 or not? I am hearing different beliefs


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