Muffler Mod, how big is too big

[timberwolf]

1.5 x .5 is plenty esp for a stock work saw.

Never found much difference related to saw size, port openings seem to be fairly porportional to displacement. Bore to stroke ratio plays a little with it as well as RPM though which affects bleed down period as well. Muffler volume factors in also. A large volume muffler is softer in terms of building back pressure right after exhaust port opens and will work with a smaller outlet than would be ideal for a small volume muffler.

 

[mtngun]

Bumping this classic thread. :rockn:

Gist of TW's tests was, muffler exit should be about 85% of exhaust port area, give or take. Beyond that, more noise and only a tiny increase in power.

But ..... TW did not use a spark screen.

I'm guessing a spark screen restricts flow considerably ?

Guess that's another test that could be done........ if someone has the time.

 

[L.R.]

Bumping this classic thread. :rockn:

Gist of TW's tests was, muffler exit should be about 85% of exhaust port area, give or take. Beyond that, more noise and only a tiny increase in power.

But ..... TW did not use a spark screen.

I'm guessing a spark screen restricts flow considerably ?

Guess that's another test that could be done........ if someone has the time.

My tach is on order... Would be fun just to duplicate the test with a different saw.

Just comparing performance before and after a specific mod can be compared to this data set, carry a pen and paper, people!

 

[timberwolf]

But ..... TW did not use a spark screen.

I'm guessing a spark screen restricts flow considerably ?

It will but depends on how the screen is positioned, if it is tight to the opening then the screen should cut the flow in about half. Something I have been thinking of doing some flow bench work on.

But if the screen is held off the actuall opening so that there is a larger area of screen availible (at leat twice the area) it likely makes little difference.

 

[OrangeRidge]

.... three years on .............

Bought a MS260Pro last week and drilled a couple of 3/8 holes in the muffler this morning . Seriously better in the cut ! This is a superb thread by Timberwolf

 

[Robin Wood]

ive been meddling with MM myself for about 2yrs now, just want to share my finding and experience as a reference or future research.

1. i see people mention after MM you have to richen the H setting because there is more air flowing in. i disagree, i read alot of posts here in this site before figuring it out. i also believe i might have same idea as Chris PA in 1 of his post, when the air moves through the carb the venturi effect is always in place. the H setting is the fuel to air ratio, once the ratio is set small change in air velocity will not make the saw run lean. as more fuel will follow(venturi effect)

2. but why does the saw still sound leaner compared to before MM ? i believe once the muffler is opened to certain point the saw runs lean because fresh air is pulled in through the new opening on the muffler during the scavenging effect. the piston downward travel creates a suction and the bigger muffler opening might allow more fresh air entry.

3. MM with tube moves peak power in the power band to lower side, somehow from my experience tube gives alot more broader power band and torque throughout the rpms. gutting and putting deflector moves rpm higher and makes more power at higher rpm. this could be tube creating better laminar flow for the exhaust gas discharge

 

[Ted Jenkins]

There is no substitute for displacement period. A smaller saw with a muffler mod will run stronger, better, cooler and with more authority. However if I would be caught with a saw without a spark screen most likely jail time. I take every precaution possible to avoid any fires and any infraction of the rules set forth by USFS and California State FS. So modding a muffler is not an option for me, but I certainly know how. Thanks

 

[blsnelling]

1. i see people mention after MM you have to richen the H setting because there is more air flowing in. i disagree, i read alot of posts here in this site before figuring it out.

I have seen the same. The L is almost always lean, but not the H like most people think.

 

[Robin Wood]

TW did mention that opening up muffler somewhere close to 200% will cause idle issues.

Now here's something interesting, i have a triple port 353 with 2 3/8ths tube welded on the top site each left and right. its got cold start idle problem, it dies off and i have to restart about 4~5 times if i dont hold the throttle. but it idles absolutely fine when warm.

To prove my theory what i did was, when cold as soon as i start the saw i plug both the 3/8ths tube with my fingers. I held it as far as i can take the heat, guess what it idled without dying and the idle actually was abit higher.

I think when you open too much, the idling fuel gets dryed out by the more amount of air entering through the opening and causing the saw hard to stay in idle

 

[Westboastfaller]

I think it effects the scavenging when you open it up as in true tuned pipe systems;
A "Smaller pipe when closest to the engine can also give more HP if tuned correctly as it have the ability to scavenge most efficient. When it's too big it won't scavenge properly resulting in hp loss as well idle g issues.
I know its a can and not a pipe but you tamper with it too much and you will effect the pulse "waves"
Yours doesn't seem to be overly opened up to what he was describing though??

Got to think about it more?

I was thinking about your first post.
I'll get back on that.

 

[Robin Wood]

I think it effects the scavenging when you open it up as in true tuned pipe systems;
A "Smaller pipe when closest to the engine can also give more HP if tuned correctly as it have the ability to scavenge most efficient. When it's too big it won't scavenge properly resulting in hp loss.
I know its a can and not a pipe but you tamper with it too much and you will effect the pulse "waves"
Yours doesn't seem to be overly opened up to what he was describing though??

Got to think about it more?

I was thinking about your first post.
I'll get back on that.

i think for tuned pipe smaller size will give more pressure during the scavenging cycle and it could give better supercharging effect and could mean increase in compression as well. but you might lose volume if the pipe size is not matched correctly with the cc range.

for canned type muffler i think its actually more complicated to determine how the exhaust gas reacts with new opening, size, location and etc. i think with more or bigger opening the scavenging zone is increased for canned muffler, so air fuel mix travels abit more closer to the exit than its used to in stock form. which could explain the temperature decrease and poor fuel economy when overly done.

i did mine based on the flange size and found out its suppose to be exhaust port size like TW mentioned here, mine's at 150% with 2 tubes. 1/2" length that sticks in and out the muffler. its the sickest sounding saw i've seen or own, its got the old muscle cam overlap sound at idle. my jaw dropped when i did timed cuts, it went from about 11+secs to 8 secs flat. what i cant believe was, stock it will stall in the cut with medium pressure in 14" hardwood. now its quite hard to even make it bog with bar fully buried in hardwood even if i lever it hard. its like a different cc saw, i will make the idling video when im free

 

[Westboastfaller]

TW did mention that opening up muffler somewhere close to 200% will cause idle issues.

Now here's something interesting, i have a triple port 353 with 2 3/8ths tube welded on the top site each left and right. its got cold start idle problem, it dies off and i have to restart about 4~5 times if i dont hold the throttle. but it idles absolutely fine when warm.

To prove my theory what i did was, when cold as soon as i start the saw i plug both the 3/8ths tube with my fingers. I held it as far as i can take the heat, guess what it idled without dying and the idle actually was abit higher.

I think when you open too much, the idling fuel gets dryed out by the more amount of air entering through the opening and causing the saw hard to stay in idle

Its doing opposite what a cold saw should do. Sometimes mine will take as long as 30 sec to settle down with fast idle off. I have had and seen a lot of 357 and 372 not want to idle cold in the winter and many without MM. I presume you can idle up or jet In but you will have to move them back when it warm?

Ok your original theory was air enters through exhaust port more, this due to an enlarged MP/ports,, this being your reasoning for the leaner behavior.
Now with the second post the revs come up when you plug the modded ports and you offered a theory. Ineresting now to start off cold again but turn throttle up a bit before hand so it idles good then plug the ports again...maybe try some leather gloves. If it can idle fine then according to your first theory the revs should drop this time?
Some food for though?
Just wondering ...you have tried different carbs..cleaned it out and all what could reasonable be done? Sounds pretty hot runs strong otherwise.
I had a Walkerized 357 with triple port 266 deflectors on. Just the way they torched out the baffle and torched the pipe off. I would hold it at about 1/8-1/4 thottle and it would hold at a real lumpy rumple and I would just crack it Just before i layed into some bush. Then back to the rumble. Sounded like a piped snowmoble. Just the way the flow would hit the jagged metal and hit the torched pipe at an angle

I agree, understanding of a tuned pipe is relatively easy to grasp. It's Calculated and the travel creates a positive presure
You can't get that effect from the can
Different animal.

 

[Robin Wood]

Its doing opposite what a cold saw should do. Sometimes mine will take as long as 30 sec to settle down with fast idle off. I have had and seen a lot of 357 and 372 not want to idle cold in the winter and many without MM. I presume you can idle up or jet In but you will have to move them back when it warm?

Ok your original theory was air enters through exhaust port more, this due to an enlarged MP/ports,, this being your reasoning for the leaner behavior.
Now with the second post the revs come up when you plug the modded ports and you offered a theory. Ineresting now to start off cold again but turn throttle up a bit before hand so it idles good then plug the ports again...maybe try some leather gloves. If it can idle fine then according to your first theory the revs should drop this time?
Some food for though?
Just wondering ...you have tried different carbs..cleaned it out and all what could reasonable be done? Sounds pretty hot runs strong otherwise.
I had a Walkerized 357 with triple port 266 deflectors on. Just the way they torched out the baffle and torched the pipe off. I would hold it at about 1/8-1/4 thottle and it would hold at a real lumpy rumple and I would just crack it Just before i layed into some bush. Then back to the rumble. Sounded like a piped snowmoble. Just the way the flow would hit the jagged metal and hit the torched pipe at an angle

I agree, understanding of a tuned pipe is relatively easy to grasp. It's Calculated and the travel creates a positive presure
You can't get that effect from the can
Different animal.

yes you are correct, if i turn in the idle it will idle right when cold but will start spinning the chain warm. the L jet expands once warm and let more fuel in which allows it to idle right ?

maybe i didnt put it in words correctly earlier. well the revs doesnt come high it just stays at the right idle like it is when warm, lets just say it idles like it should like a stock saw. this part is very tricky because at idle the gas expulsion rate is slow and alot factors can come in place. but you gave me a good idea, will try plugging the opening like you said. if im following you correctly, when i plug my fingers with idle turn a tad in it should be richer and the idle should drop ?

the saw is just 4 months old so carb and everything else is in good stock form. yeah that lumpy sound is sick, i could listen to that all day.

the turbulence in can muffler is unpredictable, gas expulsion rate reacts differently at different rpm.


very hard to figure, but when i found that saws being offered in different region with different muffler configuration i knew something was up. i've yet to see the deflectors you guys mod with in my country, not even AM mufflers with deflector. husky saws all come with the tube version. 288, 395, 372 and many others. i did my degree in manufacturing engineering, i can bet manufacturers will not do this unless there is some substantial difference. the added manufacturing, storage, tooling and etc cost will be quite a sum. from a manufacture standpoint of view, deflector should be more cost effective ? maybe the tube mufflers give more torque for the hard wood timber cutting going on here. while you guys got the high revving deflector type mufflers

 

[Chris-PA]

Every 2-stroke will lose some of it's incoming fuel/air charge out the open exhaust port when the transfers open, and will pull some air back in the open exhaust port before the transfers close. With some sort of semi-enclosed chamber on the exhaust outlet then some of that lost fuel is still sitting outside the port, so what gets pulled back in contains more exhaust and some of that unburned fuel.

At the other extreme with a wide open exhaust (no muffler), then the fuel that goes out is lost to the atmosphere, and what gets draw back into the cylinder before the port closes contains more oxygen. Any fresh air pulled into the combustion chamber through the exhaust does not pass through the carb and does not pick up any fuel, so it will lean the mixture by definition. You can tune that out, and clearly it will make the most power this way, but efficiency goes way down (due to the lost fuel). Also, it is likely to be less stable in terms of mixture control - there are two paths to get air trapped into the cylinder, one through the carb, intake, case and transfers, and the other through the exhaust. You are trying to add extra fuel into the fuel path to compensate for the raw air that comes in the exhaust, and if anything changes that balance the mixture will be wrong. That's why my muffler mods have always been mild (in addition to the noise issue).

On a cold engine some of the fuel does not vaporize and stays in droplets that don't burn, so the mixture leans out and some sort of choke/enrichment system is needed. If it's not on choke when the engine is cold it will be a little lean. I can imagine that when the engine is cold the relationship between the amount of air entering the chamber from the exhaust port vs. the case might be different too on a cold engine.

 

[Robin Wood]

Every 2-stroke will lose some of it's incoming fuel/air charge out the open exhaust port when the transfers open, and will pull some air back in the open exhaust port before the transfers close. With some sort of semi-enclosed chamber on the exhaust outlet then some of that lost fuel is still sitting outside the port, so what gets pulled back in contains more exhaust and some of that unburned fuel.

At the other extreme with a wide open exhaust (no muffler), then the fuel that goes out is lost to the atmosphere, and what gets draw back into the cylinder before the port closes contains more oxygen. Any fresh air pulled into the combustion chamber through the exhaust does not pass through the carb and does not pick up any fuel, so it will lean the mixture by definition. You can tune that out, and clearly it will make the most power this way, but efficiency goes way down (due to the lost fuel). Also, it is likely to be less stable in terms of mixture control - there are two paths to get air trapped into the cylinder, one through the carb, intake, case and transfers, and the other through the exhaust. You are trying to add extra fuel into the fuel path to compensate for the raw air that comes in the exhaust, and if anything changes that balance the mixture will be wrong. That's why my muffler mods have always been mild (in addition to the noise issue).

On a cold engine some of the fuel does not vaporize and stays in droplets that don't burn, so the mixture leans out and some sort of choke/enrichment system is needed. If it's not on choke when the engine is cold it will be a little lean. I can imagine that when the engine is cold the relationship between the amount of air entering the chamber from the exhaust port vs. the case might be different too on a cold engine.

that fuel droplet theory is quite interesting, its possible. and you are spot on how it works running without muffler.

what do you think the difference would be in a tube vs deflector muffler ? in terms of power, rpm and response

 

[Chris-PA]

what do you think the difference would be in a tube vs deflector muffler ? in terms of power, rpm and response

I'm not really sure, and I suspect there are more variables than that. For example the relationship between the outlet style and a spark screen (if any). I don't like most of the modern designs with a tiny screen perched on the outlet, because the area is too small. Other designs have a large area screen internal, which works better with an outlet tube. Of course if there's no screen that's irrelevant.

On my muffler mods I've always tried to make the flow travel the longest path internally while reducing restriction, in order to prevent mixing with external atmosphere as long as possible (and to reduce noise). I suppose an outlet tube helps do that too. I'm trying to increase the air flow/volume/velocity through the carb, but not pull more air in through the exhaust. In general, if I have to enrich the H I know I've opened it too far.

 

[Robin Wood]

i find tube muffles the noise alot better than gutting.

if you are looking to get increased airflow through the carb and restrict airflow through the exhaust. my personal take is to open 2 or 3 small openings rather than 1 very big opening

 

[BGE541]

Seems like a lot assume or think a muffler mod means you can't run a spark arrestor. Here the req is .0014" stainless mesh on federal land, which does not seem to make a bit of difference if you mod the muffler appropriately.

 

[Westboastfaller]

yes you are correct, if i turn in the idle it will idle right when cold but will start spinning the chain warm. the L jet expands once warm and let more fuel in which allows it to idle right ?

What is YOUR definition of warm? A bit of revving or is it cutting wood and getting heat into it?

The carb temperature shouldn't really get warmer In use. It should stay the temperature of the air blown opon it.
If you would like to clear any doubt about contraction/expansion in the orifice then put a hair dryer ...er...um I mean heat gun on the top of the carb for a sec then start it. You will get your answer.

maybe i didnt put it in words correctly earlier. well the revs doesnt come high it just stays at the right idle like it is when warm, lets just say it idles like it should like a stock saw. this part is very tricky because at idle the gas expulsion rate is slow and alot factors can come in place. but you gave me a good idea, will try plugging the opening like you said. if im following you correctly, when i plug my fingers with idle turn a tad in it should be richer and the idle should drop ?

Yes we are on the same page. I took it as that. Maybe top idle revs don't change but if the bigger port fluctuates down ...She stalls.

Yes that's what I'm saying you are basically double checking your 'math'
If it works one way it should work opposite the other..or we are going to find out why.....I have a feeling...lol
You should at least see differences when it's warm.
It seems you proved it doesn't run probably cold with that percent of opening.
Between your findings and my extreme cold experience leads me to believe the difference may be the ignition temp, less expansion in cold volumed air molecules,
inability to clear the extra emmisions on cold starts

the saw is just 4 months old so carb and everything else is in good stock form. yeah that lumpy sound is sick, i could listen to that all day.

the turbulence in can muffler is unpredictable, gas expulsion rate reacts differently at different rpm.

Nothing like the old school pipes
Pretty cool that they make then out of round stock from factory. Obviously it is better. Bob Walker, Walkerized saws former World Campion Race SAW Builder always used triple port with pipe horns on all his worK saws. The deflectors was a taimed down look as they have been working side by side with WCB for 25 yrs.
Initially they was a noise issue. It's a Grey area here in BC as are mod saws so we have to make them more natural looking.

I would have to say from '89 to prevent, I have done very well will Husqvarna. Never have warmed up to Zama carbs.
I believe one of their early Introductions was on the 365 that didn't go that well then they switched bach to Wardro.

the turbulence in can muffler is unpredictable, gas expulsion rate reacts differently at different rpm.

Temps ect...
The cross scavenging engine style is also unpredictable as it's ability to do just that
Is limited to low Rpm.. I always liked the dome piston it aids in the process acting as a deflector.

 

[bikemike]

i think for tuned pipe smaller size will give more pressure during the scavenging cycle and it could give better supercharging effect and could mean increase in compression as well. but you might lose volume if the pipe size is not matched correctly with the cc range.

for canned type muffler i think its actually more complicated to determine how the exhaust gas reacts with new opening, size, location and etc. i think with more or bigger opening the scavenging zone is increased for canned muffler, so air fuel mix travels abit more closer to the exit than its used to in stock form. which could explain the temperature decrease and poor fuel economy when overly done.

i did mine based on the flange size and found out its suppose to be exhaust port size like TW mentioned here, mine's at 150% with 2 tubes. 1/2" length that sticks in and out the muffler. its the sickest sounding saw i've seen or own, its got the old muscle cam overlap sound at idle. my jaw dropped when i did timed cuts, it went from about 11+secs to 8 secs flat. what i cant believe was, stock it will stall in the cut with medium pressure in 14" hardwood. now its quite hard to even make it bog with bar fully buried in hardwood even if i lever it hard. its like a different cc saw, i will make the idling video when im free

I love the chit out of my 49cc piped echo clamshell saw good strong runner and holds nice rpm in the cuts very responsive on the throttle too