The mystified muffler mod

[buttercup]

I was initially curious about muffler mods and found several threads mostly on this site, and it's interesting to read about people's experiences but there have been very little calculated info to hold on to other than - "open it up a little".
The closest thing to calculation I did find was that the muffler port should be about 80% of the cylinder exhaust port, that is at least something to go on - however...

I dug up an article on making silenced performance enhancing mufflers (not tuned pipe) to high performance 2-stroke model engines, this article is about a famous and well proven design (in my country at least) that goes back several decades and is still in use with nothing to surpass it - except a tuned pipe of course.

The article contains a plan drawing for a 10ccm (.60ci) engine and a formula sheet for all dimensions based on engine displacement, these engines are operated at about the same rpm as a chainsaw. The muffler itself would be too big for a chainsaw and it should also ideally be adapted in length from the cylinder according to rpm which would also be difficult with a chainsaw, but the relations between engine displacement and muffler port is actually quite interesting.

(Metric)
The exhaust port formula is quite simple: 2 V(root) 2.03 x displacement = diameter
So, with a 72ccm displacement 2.03 x 72 = 146.16
Formula: 2 V(root) 146.16 = 24.179330016
Answer: a suitable total area for the muffler port(s) on a 72ccm 2-stroke engine is equal a circular area at about 24mm in diameter, that equals two circular areas at about 17,5mm.

Compared to my 381 kit saw the total muffler port area (2 ports muffler, 18mm circular + two vent slots) is about 400sq mm, it should be (according to the formula) at about 450sq mm.

(Edited)

 

[livemusic]

I was initially curious about muffler mods and found several threads mostly on this site, and it's interesting to read about people's experiences but there have been very little calculated info to hold on to other than - "open it up a little".
The closest thing to calculation I did find was that the muffler port should be about 80% of the cylinder exhaust port, that is at least something to go on - however...

I dug up an article on making silenced performance enhancing mufflers (not tuned pipe) to high performance 2-stroke model engines, this article is about a famous and well proven design (in my country at least) that goes back several decades and is still in use with nothing to surpass it - except a tuned pipe of course.

The article contains a plan drawing for a 10ccm engine and a formula sheet for all dimensions based on engine displacement, these engines are operated at about the same rpm as a chainsaw. The muffler itself would be too big for a chainsaw and it should also ideally be adapted in length from the cylinder according to rpm which would also be difficult with a chainsaw, but the relations between engine displacement and muffler port is actually quite interesting.

The exhaust port formula is quite simple: 2 V(root) 2,03 x displacement = diameter
So, with a 72cc displacement 2,03 x 72 = 146,16
Formula: 2 V(root) 146,16 = 24.179330016
Answer: a suitable total area for the muffler port(s) on a 72 cc 2-stroke engine is equal a circular area at about 24mm in diameter, that makes two circular areas at about 17,5mm.

Compared to my Jurassic 381 kit saw the total muffler port area (2 ports muffler, 18mm circular + two vent slots) is about 400sq mm, it should be (according to the formula) at about 450sq mm.

Very interesting. Keep us posted if you figure anything out for a proper muffler mod!

I had to look it up, you are in Norway. Looks like you probably have lots of trees, lots of water. Or ice.

 

[Brent Adams]

Makes sense to me.
Also, for those that arent familiar, commas are substituted for decimal points in some areas.
Do not use commas and add zeros.

 

[NSEric]

That formula works out pretty close to what you see on saws. ie one 25mm pipe for the muffler outlet or 2 close to 18mm on a 72cc saw for max power.
Most guys myself included don't go that far, its has nothing to do with power, the saws are pretty loud with the best for power sized outlets so we go a little smaller making a compromise between power and noise.

 

[cuinrearview]

This is about right. 52cc

 

[buttercup]

Very interesting. Keep us posted if you figure anything out for a proper muffler mod!

I had to look it up, you are in Norway. Looks like you probably have lots of trees, lots of water. Or ice.

Lots of trees yes, mostly Birch and Fir wood. I have a Husqvarna 445 for regular use - firewood I depend on for the winter and helping the neighbor to clear out vegetation.
I would not consider modding it in any way, it does what it should and I like it just as it is.
The 038/380 kit saw I use for milling, just a hobby. Making or building something yourself is cool, but making or building something yourself with materials you harvested and refined yourself directly from the woods - is an awesome thought.

 

[Ronie]

This is about right. 52cc
View attachment 752011

Now that's an ugly muffler!

 

[scottr]

Has anyone tried the phosphoric acid type rust nutralizer (ospho) to change the iron oxide to a black iron phosphate insead of painting ?

 

[Nathan Graff]

Has anyone tried the phosphoric acid type rust nutralizer (ospho) to change the iron oxide to a black iron phosphate insead of painting ?

Friend of mine uses RustMort on car bodywork. Works as you describe. Creates a hard black iron phosphate that's hard to scratch.

You could also boil the part in water with a very little bit of acid in it. When I say a very little bit, I mean less than a teaspoon per gallon. It's called a cold rust bluing process. That being said, you have to keep that finish oiled to keep the rust from reforming.

 

[Ronie]

Has anyone tried the phosphoric acid type rust nutralizer (ospho) to change the iron oxide to a black iron phosphate insead of painting ?

I've used it but like Nathan Graff said it will start rusting again if you don't oil it or paint it.

 

[cuinrearview]

Why you guys trying to make em pretty?

 

[ColdNorCal]

Corroseal rust converter also works good.

 

[buttercup]

This is about right. 52cc
View attachment 752011

My first thought is "that is one huge muffler port", is there a spark catcher in there?
Someone said ugly, I'd say nicely welded - because silver solder would have a slightly different color to it.
I would silver solder because that is what I have at hand and is familiar with, and I would use two smaller pipes.
No doubt it roars though, have you tried different tube sizes before you ended up with that one or did you just want it to be "big enough" right away?
That is nicely done work anyway, could probably have been better preserved though.

 

[Ted Jenkins]

Muffler mods work very well and it is almost that no one will go wrong performing mods on mufflers. Performance will increase. However one issue is noise. I can not afford any increase in the noise level. I work with the USFS quite a bit and any thing that would bring attention to me is unaffordable. I also do work in residential areas so the time to make mods will not work for me. When ever I have a need to pull a muffler and I have enough room I will enlarge the whole unit while keep ing noise level very tolerable. Thanks

 

[Huskybill]

Why you guys trying to make em pretty?
View attachment 752219

I even waxed my saws keeping them purdy I was a field salesman for my local dealer I would demo saws too. Once these guys seen my huskys cut they ran to my dealer and bought one. I just wanted to thank my dealer for his good service.

 

[Huskybill]

So gentlemen I cut my 2100 muffler in half verticle, then do what mods I need to do, clean the carbon and metal chips out of it then weld it back up right.?

I’m going to add the lower louver exhaust port. Do you remove any baffles or leave them?

It’s my excuse to get a new MIG welder.

 

[buttercup]

So gentlemen I cut my 2100 muffler in half verticle, then do what mods I need to do, clean the carbon and metal chips out of it then weld it back up right.?

I’m going to add the lower louver exhaust port. Do you remove any baffles or leave them?

It’s my excuse to get a new MIG welder.

So, if you have some kind of baffle box or plate in there with holes in it, those holes should "together" be a slightly larger area than muffler outlet port(s).

 

[Woodslasher]

I want to puke when I see that muffler @cuinrearview. But, having cleaned up LOTS of tools that looked like that, I'll share some wisdom. If you vinegar soak it and then lightly sand it with a block and some 220, you'll have the coolest etched-looking muffler on the block.

 

[buttercup]

So gentlemen I cut my 2100 muffler in half verticle, then do what mods I need to do, clean the carbon and metal chips out of it then weld it back up right.?

I’m going to add the lower louver exhaust port. Do you remove any baffles or leave them?

It’s my excuse to get a new MIG welder.

As the 381 as an example;
Originally the baffle box consists of 16 - 6mm holes, together about 450sq mm.
The muffler ports together about 400sq mm.

Modified; 2 extra 6mm holes in the baffle box makes about 500sq mm.
Two 17,5 mm outlets makes about 450sq mm, according to the formula mentioned.
But it already has a 18mm outlet (about 250sq mm) and the two vertical vents is about 75sq mm each - so I could just add another vertical vent and it would be it.

 

[Nathan Graff]

So gentlemen I cut my 2100 muffler in half verticle, then do what mods I need to do, clean the carbon and metal chips out of it then weld it back up right.?

I’m going to add the lower louver exhaust port. Do you remove any baffles or leave them?

It’s my excuse to get a new MIG welder.

It's likely that MIG will be to hot and burn holes through your muffler if you try to weld a continuous bead. You'd have to step into a very high end MIG with infinite adjustments to get one that would weld that continuous. TIG would be better, and you can braise and silver solder with TIG as well.