Muffler mod etiquette.

[Marley5]

I'm an older guy, loner, quiet, non confrontational.
BUT I've watched and listened to so many videos and threads regarding muffler mods and most are half as*ed. Imo

Coming from the muscle car era of the 70's we put all our money in our cars to make them run faster for the big weekend drag racing.
Headers were a must to open up the exhaust but a common mistake was big pipes with no back pressure.
The car sounded great but couldn't even break traction.
Chainsaws:
Why are there so many YT videos of those gutting mufflers and opening up the exit bigger than the import, piston side.
In my mind this actually creates performance loss compared to stock form.
Yes, I guess I've watched to many videos this evening with excessive drilling and high reving Dremels.
Educate me

 

[Chevboy0167]

Main advantage...... heat removal. Keeps cylinder temps down. Engine as a whole runs cooler. Extends life of saw as a whole.

I believe rule of thumb is open up muffler outlet up to 70% of cylinder exhaust port size.

 

[jblnut]

There is something to be said about keeping a similar internal volume to the muffler can as well. I put a Bark Box on my 066 and thought it ran better, which I think it actually did. I recently put the stock cover back on and opened up the stock hole to around that 70% of the exhaust opening and I’m 100% sure it is running better and pulling harder.

 

[osadayo99]

We run WCS bark boxes on all our Stihl 362, 461/2 and 500i saws. Don't know so much about "more power" but they definitely run cooler and throttle response is much improved . Our crew works Wildfire and fire mitigation thinning in surrounding mountains ...during the summer months we're on those saws for long days, just the fact that they run cooler is worth the mod. Quicker throttle response eases the limbing and slashing process. Just my / our observation do'n the work on the ground.

 

[Patrick62]

I have modified a few mufflers over the years. Nothing ridiculously crazy tho.
You have to think about the whole system as it is a resonant (for lack of a better term) setup.
Look at the enduro motorcycles, and that giant expansion chamber. The plan is that the exhaust will cool, and create some vacuum to pull the next puff of exhaust from the cylinder. However... if there is too much, then it pulls more unburned charge.
At a certain rpm, the thing will work like a charm. The black magic is to make the thing really hot where you are at when cutting.
This opens up the next "rabbit hole" to fall into.
Porting... I have run two saws that were ported, and the results are there. This is where the mechanic figures by experience, and a bunch of scribbles on a paper, what to make each port based upon, carb size, exhaust size, CC of cylinder, etc.

Correct assessment, louder isn't always more power.

I do like that 70% measurement, and seems to be a good number to shoot for. removing the spark screen, it's your call.
Could get in trouble with some authority figures. I have a couple saws that are compromised this way....

 

[Fried Chicken]

There is something to be said for quiet tools

 

[rogue60]

Four strokes and two strokes are completely different engines!
And to make matters worse a chainsaw is an industrial two stroke.
Yeah I'd probably stop thinking you are clever believing 70's muscle cars exhaust systems apply to industrial two strokes

 

[toppers]

It depends on the saw and how restricted the can originally was, and I agree that sound =/= more power and can in fact just be a nuisance.

-On my 261C I put a WCS deflector that requires a huge cut out. The sound was so bad I needed foam earplugs AND ear defenders. Since then I've closed it off with an aluminum strip and drilled 2x 1/4" holes as a compromise. Now I feel it is running better than stock and when it had a huge opening.

-On my 7310p the muffler is almost entirely opened already except for a metal snorkel inside. I just added a deflector and added 2x 1/4" holes with a screen. It seems the best mix of cooler running + pleasant sound, not annoying. Can I claim more power? Not really since this thing already rips as-is after a retune and break in.

Point being: Yes they seem to improve these saws marginally, but it's about finding that sweet spot. A wide opened obnoxious can is a bad time and nuisance to your neighbors.

 

[sean donato]

Can mufflers are just noise deadening devises, there is zero sound resonance/ waves deflecting anything back into the combustion chamber like a tuned pipe. Back pressure isn't good for any practical purpose on one of these engines, even less so on a stratto saw. All you're doing is keeping heat in the saw. Loop scavenged non tuned exhaust engines are all about easy movement of air through the engine. Bottling them up is nothing more then a restriction to the system.
Most saws will benefit from some sort of "muffler" mod and tune tweak. Depends on the saw for how much. Generally the 70% of exhaust area (like mentioned) is the default outlet size to shoot for. Like many others, the older I get the less I like obnoxiously loud exhaust in saws. (Or anything else for that matter.) So I generally try to strike a balance between restrictive exhaust and noise deadening.

 

[Fried Chicken]

Can mufflers are just noise deadening devises, there is zero sound resonance/ waves deflecting anything back into the combustion chamber like a tuned pipe. Back pressure isn't good for any practical purpose on one of these engines, even less so on a stratto saw. All you're doing is keeping heat in the saw. Loop scavenged non tuned exhaust engines are all about easy movement of air through the engine. Bottling them up is nothing more then a restriction to the system.
Most saws will benefit from some sort of "muffler" mod and tune tweak. Depends on the saw for how much. Generally the 70% of exhaust area (like mentioned) is the default outlet size to shoot for. Like many others, the older I get the less I like obnoxiously loud exhaust in saws. (Or anything else for that matter.) So I generally try to strike a balance between restrictive exhaust and noise deadening.

 

[bwalker]

All new saws benefit from opening up the muffler. Both HP wise and heat reduction wise.

 

[bwalker]

That motor has a tuned pipe. A saw doesn't not have any such thing.
What @sean donato said was spot on in every regard.

 

[drumbum]

Referring to a muffler as a bark box gains 20% in power minimum!


lol

 

[bwalker]

Referring to a muffler as a bark box gains 20% in power minimum!


lol

I have a bark box for my 400C. It makes more power for certain, but is obnoxiously loud.

 

[Patrick62]

I modified my 261cm, the stock muffler was incredibly dinky on the outlet.
Brazed in a hunk of 3/4 EMT about 1 1/2 inch long to get it past the clutch cover.
Id on that pipe is about .8 sq inch, and the m tronic adjusted itslelf to that. Yeah it is noisy now, but pulls a lot harder.

If you try and run a saw with NO muffler you will discover that it is there for a reason. The thing would barely start, and not wrap up like you think it would. Has to have something to get the gases to flow. A 290 stihl taught me that one. fixed the muffler back onto it, and she run like it should.

 

[NSEric]

Some saws are really choked up in the muffler.
I recently bought a 590 echo, it was super quiet and choked up.
I like to find a happy medium between really loud and stock.
I did a mild mod to it, making the opening a little bigger and opening up the internal baffle, I dont want it to be too loud. I know it will have a bit more power with no baffle at all but dont want the noise that comes with that set up.
My 660 clone is only used a bit and not next to others often, it's quite loud but alright due to how I use it.

 

[82F100SWB]

That motor has a tuned pipe. A saw doesn't not have any such thing.
What @sean donato said was spot on in every regard.

Not only is the typical saw muffler just a pressure box to kill noise, most saws have very short blowdown compared to applications that typically use a pipe, which severely limits the time that a proper pipe would have to do its thing in the first place.
Saws are usually ported around getting the exhaust out as fast as possible, not taking advantage of a pressure wave from the pipe.