Muffler Mod Where and How Much?

[ballisticdoughnut]

That’s not technically true with a 2 smoker you need sufficient back pressure with scavenging effect.

Back pressure has nothing to do with scavenging. It does kill performance though. Your referring to pressure wave tuning, and chainsaw mufflers do a terrible job at it. I’m not saying go drill a gigantic hole in your muffler and call it a “mod”. Enlarging the factory outlet to 70% of exhaust port area is plenty.

 

[C George]

Pretty much all engines except blown ones need the correct back pressure to make good power

 

[thompsoncustom]

there is a thread on here somewhere where a member "timberwolf" I believe, took a muffler and welded it shut and then did tested slowly opening it up a little at a time and testing. if I remember correctly up to 170% of the bore was great for gains bit after that it had issues idling and most of those gains where made by 125% of the bore.

he did take it all the way to 400% of the bore and it made the most power but it was only like 10% more then 170%.

 

[ballisticdoughnut]

Yes but most 2 stroke intakes , especially many Stihl pieces of eq. that I work on are highly restricted for long service life

True. That’s why most of my saws are from early 80’s to mid 90’s. Good old piston ported power. Only strato saw I own is a 545 Mark II.

 

[C George]

The Stihl O series saws run great

 

[WheelHorseFan]

Simple muffler mods will give you a little more power, make the saw breath better and sound louder... port and polishing the cylinder head will give you more. An unlimited coil helps too. Decking/squashing the cylinder and other machining techniques will go further if done right... then we get into race saws with nitrous, methanol and tuned pipes....

Race saws with Nitro?
Wait' now how you hold on through the 1/8th mile? Good thing thay shortened tracks from 1/4 mile.
I never saw their point there, but now I saw why they went'n did it. I didn't see da saws, prolly just too fast to see'm.

 

[Husqy41]

- last top end built (cast iron sleeve mod w. 40mm Meteor piston.)



- first break in procedure with ported open port cylinder...

 

[Husqy41]

 

[Exophysical]

Husqvarna 350 , 44mm cyl I believe

Not sure how similar this is to the 345 I did, pretty similar I think.

I opened the stock port up quite a bit, to an estemated 75-80% of inlet hole. Results were a bit meh, and I realised exactly how big that inlet port is for the size of saw. Way bigger than my 55, probably the same size as my 372, so I made up a peice of sheet metal to mount in place of the spark arrest screen and partially cover the port. After a bit of experimenting I was able to see some gains in throttle response and pull.

 

[singinwoodwackr]

Not sure how similar this is to the 345 I did, pretty similar I think.

I opened the stock port up quite a bit, to an estemated 75-80% of inlet hole. Results were a bit meh, and I realised exactly how big that inlet port is for the size of saw. Way bigger than my 55, probably the same size as my 372, so I made up a peice of sheet metal to mount in place of the spark arrest screen and partially cover the port. After a bit of experimenting I was able to see some gains in throttle response and pull.

Did you make up a chart or something to record results?

 

[Exophysical]

Did you make up a chart or something to record results?

No, It was just taking a snip off the sheet metal and making a couple cuts with the saw to see how it felt.

 

[royaleblue]

My brazing torch arrived today and I'm going to attempt my first muffler mod on a 562XP Mark 2. This is the first time I've brazed since high school metals. I'm going with a 1 inch pipe tilted slightly towards the bar. My idea is to go with some kind of threaded pipe so I can cap the pipe and reroute exhaust through the OEM deflector to quiet it down when needed. Given that it's threaded it'll likely have to be thicker pipe than typical used for muffler mods. Here's my questions:

1. Are there certain kinds of metal that can't be brazed together? Are there metal interactions I need to watch out for? I was surprised to find out copper has a very high melting point and can be brazed to steel. I might be looking for pipe in the plumbing department.

2. Does anyone know where I can source the thinnest threaded pipe at a Home Depot that would work for my idea? Anyone recommend a type of brazing sodder?

 

[Ed Penney]

Use thinner tubing, not pipe, don't thread it, just make a spark arrestor/silencer with a stainless clamp. Big box stores don't have much selection. You might find something cool and unique to design your muffler at a salvage yard or a metal recycle center.