Muffler Mod, how big is too big

[Chris-PA]

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

I think the sound level and all the flow characteristics of the muffler are related. Ideally you'd want a muffler that took in all the pulsations from the exhaust port and had an outlet that just emitted the average flow without any pulsations at all. There would be no flow back into the exhaust. In practice that's not really possible, especially with small can sizes. Look at what it takes to make a quiet car exhaust, which usually has multiple stages, and it still ends up restricting the flow to some extent. Also, the acoustic and filtering characteristics of the muffler are fixed, while the engine fundamental rpm changes quite a bit, so it can never really match everywhere.

Essentially the muffler is analogous to a passive low pass filter, which will always have some restriction (loss) in addition to whatever filtering it is doing.

It's possible using multiple smaller outlet holes could help block some of the lower frequency pulsations compared to a single outlet with equivalent effective area, but this will depend on a lot of other things about how the muffler is constructed. Is is a single large can or does it have other internal baffles? It might be that an internal baffle has already reduced those frequencies, and then the multiple outlet holes won't matter much. I've done both single and multiple outlets, it depends on the rest of the design.

 

[Robin Wood]

[QUOTE="Robin Wood, post: 6321033
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

I think the sound level and all the flow characteristics of the muffler are related. Ideally you'd want a muffler that took in all the pulsations from the exhaust port and had an outlet that just emitted the average flow without any pulsations at all. There would be no flow back into the exhaust. In practice that's not really possible, especially with small can sizes. Look at what it takes to make a quiet car exhaust, which usually has multiple stages, and it still ends up restricting the flow to some extent. Also, the acoustic and filtering characteristics of the muffler are fixed, while the engine fundamental rpm changes quite a bit, so it can never really match everywhere.

Essentially the muffler is analogous to a passive low pass filter, which will always have some restriction (loss) in addition to whatever filtering it is doing.

It's possible using multiple smaller outlet holes could help block some of the lower frequency pulsations compared to a single outlet with equivalent effective area, but this will depend on a lot of other things about how the muffler is constructed. Is is a single large can or does it have other internal baffles? It might be that an internal baffle has already reduced those frequencies, and then the multiple outlet holes won't matter much. I've done both single and multiple outlets, it depends on the rest of the design.[/QUOTE]

man you just brought the discussion to whole new level. i have no idea what you just said lol. but rock on bro.

this is a diferrent league now.

@westboasfaller that hair dryer trick will definetely clear my doubt, awesome idea buddy

 

[Robin Wood]

@Westboastfaller

i took out my 353 for some quick fellings
was in a hurry but i did the hot pipe plugging test. you were right dude the idle came up, almost high enough to spin the chain intermittently

what does that mean ?
must be something

i dont have time to goof around, im sitting for my ISA arborist exam this sunday. the questions are based on temperate climate -__-, i hope i dont get shafted. wish me luck, will be back soon

 

[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

@Westboastfaller

i took out my 353 for some quick fellings
was in a hurry but i did the hot pipe plugging test. you were right dude the idle came up, almost high enough to spin the chain intermittently

what does that mean ?
must be something

i dont have time to goof around, im sitting for my ISA arborist exam this sunday. the questions are based on temperate climate -__-, i hope i dont get shafted. wish me luck, will be back soon

Awesome, definitely all my best Robin!
I may be doing mine soon and start getting more into the consulting/riparian prescriptions. I'm addictied to cutting though. I'll have to have some side stuff to satisfy my need.

I originally said to Turn Up The Idle and start it then plug the mod ports right away When It Was Cold. On my second thought... was not to raise idle and to try plug TP warm as It would make for more conclusive testing considering the TP only had problems idling when on cold starts. (That's what you did right?)
*But I thought it would have done the opposite, that the revs would come down
Not up?
Let's do a recap
SP will idle cold
Sp the clutch wants to engage as it warms
TP stalls cold
TP idles warm


We both offered possibilities for the TP having difficulty running at an idle cold.
Had the idle dropped when plugging the TP when it was warm then it still would have left it as no closer that "it doesn't run well at that percent of exhaust opening" leaving our theories inconclusive.

I/We expected TP was having trouble ONLY cold for reasons given in pryor post. Revs came up with the TP when warm. Revs should have stayed the same with stock SP. ...meaning they would have needed to drop when plugging the warmed up TP.
Make sense...Or Are You AS Confused As I am?..lol

In a nut shell. The revs are comming up on the stock muffler as it warms up too.

*Why didn't I say that to begin with ???....that wouldn't be any fun*

So what does that mean you ask?
This saw hand says Properly running cold carberated engines don't run that way.
Revs drop down to idle when ready ...not come up.
I'm basically back to my earlier thought again now after us 'exhausting' that avenue (bad pun I know)
It's a carb issue it would appear Robin.

 

[Robin Wood]

Awesome, definitely all my best Robin!
I may be doing mine soon and start getting more into the consulting/riparian prescriptions. I'm addictied to cutting though. I'll have to have some side stuff to satisfy my need.

I originally said to Turn Up The Idle and start it then plug the mod ports right away When It Was Cold. On my second thought... was not to raise idle and to try plug TP warm as It would make for more conclusive testing considering the TP only had problems idling when on cold starts. (That's what you did right?)
*But I thought it would have done the opposite, that the revs would come down
Not up?
Let's do a recap
SP will idle cold
Sp the clutch wants to engage as it warms
TP stalls cold
TP idles warm


We both offered possibilities for the TP having difficulty running at an idle cold.
Had the idle dropped when plugging the TP when it was warm then it still would have left it as no closer that "it doesn't run well at that percent of exhaust opening" leaving our theories inconclusive.

I/We expected TP was having trouble ONLY cold for reasons given in pryor post. Revs came up with the TP when warm. Revs should have stayed the same with stock SP. ...meaning they would have needed to drop when plugging the warmed up TP.
Make sense...Or Are You AS Confused As I am?..lol

In a nut shell. The revs are comming up on the stock muffler as it warms up too.

*Why didn't I say that to begin with ???....that wouldn't be any fun*

So what does that mean you ask?
This saw hand says Properly running cold carberated engines don't run that way.
Revs drop down to idle when ready ...not come up.
I'm basically back to my earlier thought again now after us 'exhausting' that avenue (bad pun I know)
It's a carb issue it would appear Robin.

thanks dude
you should, its really an eye opener. good info and gave me whole different level of understanding and troubleshooting in this field
im more of a transplant addict, sawing comes 2nd for me. but since its the most discussed stuff here might as well get used to it lol.
nothing beats the feeling of lifting something huge and with heavy equipments with the level of planning and precision involved
and bringing it elsewhere while everyone looks in awe. not to mention the nail biting moment to see if it survive. i like the adrenaline

i havent done that yet
but yes thats what happened like i described

revs come up when TP plugged when hot
yes our expectation was total opposite
and yes im as confused as you are or even more !!! lol

its not carb issue, the saw is pretty new. it runs fantastic
we are meddling with air movement here, so any change in direction/volume/velocity
will create a butterfly effect, it could be when TP is plugged more exhaust gas could be going inside the chamber
and making the combustion lean ? when TP is open the gasses are out and more mix is being scavenged back into the chamber ?
in return producing the exponential power gain, it is simply nuts. i cant imagine how it will run if its ported and gasket delete