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Author Topic: Muffler mods  (Read 7048 times)

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Offline Air Lad

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Re: Muffler mods
« Reply #60 on: March 12, 2019, 06:45:45 AM »

(Image hidden from quote, click to view.)
 
Here's my Echo 490 muff mod.
Pretty straight forward. Tossed the highly restrictive deflector, removed screen(but kept in case I want to cut on national forest land), pulled restricter tube and flipped facing out.

It runs and sounds real good. Thumpety-thump. But not too loud.
Removable for other applications?
Ms 170/260c /039...Husk 142e/240e...Unloved Chinese 51.2cc that hasn't done anything wrong...2 x dead Mculloch's ..Vintage Poulan.. and a vintage Echo that still runs beaut

Offline Inaotherlife

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Re: Muffler mods
« Reply #61 on: March 12, 2019, 06:34:37 PM »

(Image hidden from quote, click to view.)
 
Here's my Echo 490 muff mod.
Pretty straight forward. Tossed the highly restrictive deflector, removed screen(but kept in case I want to cut on national forest land), pulled restricter tube and flipped facing out.

It runs and sounds real good. Thumpety-thump. But not too loud.
Removable for other applications?
I'm not sure I am understanding the question.
All three pieces: the deflector, screen, and restrictor tube were bolted onto the outside of the can. I flipped the restrictor tube facing out, instead of in, drilled two holes in the opposite corners, and screwed it down.

Offline weimedog

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Re: Muffler mods
« Reply #62 on: March 12, 2019, 08:20:42 PM »
To the earlier autotune question. Unless its radical, Autotunes don't care. A lot of over analysis relative to them. They will play their simple game regardless. The only theoretical issue is you create a build that will require more fuel than they can provide...and a typical muffler mod isn't doing that. AND that's with any carburetor as even those the autotune label sounds cool...its still a freakin carburetor. 

( TO review, auto tunes do lean tests continually over short periods of time and this is done my holding the fuel Solenoid shut for a few RPM's if the saw speeds up, that means the prior mixture setting was too rich, if it slows down, that means it was too lean. based on what happens the system adjusts fuel supply by holding that cycling solenoid closed for a little more or less time while its cycling. Holding it closed for a bit longer per cycle leans things, and the converse is true. It does this iteration non stop while the saw is running shooting for max RPMs under throttle....regardless of surrounding issues. You have a dirty fuel filter...that lean out test shows a little rich and it adjusts.....an air leak...a little lean and it adjusts. A muffler mod...and it adds fuel to compensate. )

( BTW on my built 562's I do see changes in the fuel settings after they have had time on them. Typical the low end drops to the 35-40 on cst fuel setting numbers and the high stays in the 50-60 range. When I have a larger muffler outlet than my typical build, I've seen that low speed number drop into the 20's. It's dumping fuel at that point out the exhaust. But doesn't seem to change the high side. Standard on those arbitrary unit CST numbers is 75 and it works from there. Those numbers are about units of time the solenoid stays closed. Lower the number the less time its closed therefor MORE fuel or a richer mixture. Higher number and its staying closed longer therefore a leaner mixture.)
Husqvarna 365sp/372xpw Blend, Jonsered 2171 51.4mm XPW build,562xp HTSS, 560 HTSS, 272XP, 61/272XP, 555, 257, 242, 238, Homelite S-XL 925, XP-1020A, Super XL (Dad's saw); Jonsered 2094, Three 920's, CS-2172, Solo 603; 3 Huztl MS660's (2 54mm and 1 56mm)

Offline Air Lad

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Re: Muffler mods
« Reply #63 on: March 13, 2019, 05:30:45 AM »

(Image hidden from quote, click to view.)
 
Here's my Echo 490 muff mod.
Pretty straight forward. Tossed the highly restrictive deflector, removed screen(but kept in case I want to cut on national forest land), pulled restricter tube and flipped facing out.

It runs and sounds real good. Thumpety-thump. But not too loud.
Removable for other applications?
I'm not sure I am understanding the question.
All three pieces: the deflector, screen, and restrictor tube were bolted onto the outside of the can. I flipped the restrictor tube facing out, instead of in, drilled two holes in the opposite corners, and screwed it down.
I was curious mate because I have thought about a two stage exhaust setup where you can be loud and proud out on acreage but slip in a plate and re tune for urban use.The neighbours may be a little less unimpressed.
Did you're reversing result in any better flow, or raised noise level
Cheers
Ms 170/260c /039...Husk 142e/240e...Unloved Chinese 51.2cc that hasn't done anything wrong...2 x dead Mculloch's ..Vintage Poulan.. and a vintage Echo that still runs beaut

Offline MAF143

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Re: Muffler mods
« Reply #64 on: March 14, 2019, 05:29:08 PM »
 As for tuned pipes pushing charge back in, i dunno.  Im having a hard time with that.   Ive long been under the impression that Inert, spent gas always contaminates a fuel charge


Not sure I can explain it well but on a "piped" 2 stroke the expansion chamber at resonance (tuned RPM or "up on the pipe") first creates low pressure at the cylinders exhaust port that scavenges all the "spent gas" out of the combustion chamber, plus pulls through some additional "unspent" fuel and air mixture.  The unburnt mix and the exhaust gases don't mix much in the small diameter portion of the pipe and stay pretty much seperated.  As the pressure wave hits the back of the expansion chamber in the pipe and reflects back with a high pressure wave, it "stuffs" the unburnt fuel mix back into the cylinder as the exhaust port is closing.

pictures or a video would be very helpful, but sadly I'm not that guy...

The relationships of the dimensions of the pipe all contribute to the "tuning" of the the expantion chamber along with the port timing / sizing.  The length, diameter, and taper of the "megaphone" portion of the pipe all works with the port timing and determines the power peak and width in the RPM band of a 2-stroke when up on the pipe.  Tuning of these are very scientific for larger companies that can afford lots of R&D time.  For us weekend warriors on a dirt bike or older quad, it is more black magic and voodoo.  I understand the concepts pretty well, but have never jumped into the math of tuning a resonant circuit of differing specific gravity gasses (hot "spent" vs. fuel mix).  My brain cells are in pain just thinking about it.  Too much fun in the seventies...  The right pipe coupled with the proper port timing can develop a ton-o-power out of a small 2-stroke.

Dirt bikes, go carts, snowmobiles, jet skis and quads are large enough that tuned pipes can be fitted by the factory or even aftermarket stuff added to alter the tuning.  I have an old beater quad from the late 80's that was a lot of fun to port and learn some of this stuff on.  You can even add a boost bottle on the intake side to "tune" the intake to stuff more fuel / air mix in at the lower RPM to get better bottom end torque so the 4-stroke guys don't leave you in the dust due to a 2-stroke having a narrow power band and lot's of shifting gears to make up for it.  But these days the best performance mod I could do for my quad would be to lose about 70 pounds...  

All that said, chainsaws for work use don't have the luxury of adding a big ole expansion chamber (yet)...  I have done muffler mods on both saws I use regularly out in the woods away from neighbors and they perform very well.  I'm no expert, but my thoughs are that I try to get the muffler exit hole(s) area to approximately equal or a tad larger the opening at the cylinder's exhaust port.  I try to not make any straight lines between the in and out of the muffler so foreign objects have very low possibility of getting into the exhaust port of the cylinder.

Mike's reply #10 in this thread has some very good points on this as well.

I wish I had done more before and after info collection before I had done my mods.  Stuff like cookie cutting times, muffler temps during cuts, db levels etc...
Always having a great day!
MS 391, MS 250, HM-126, Ferguson TO-35, '97 Ram 1500 wood cuttin' truck, splitter, Woodland Mills Grindlux 4000 sharpener, Vogelzang Ponderosa keeping us warm

Offline HolmenTree

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Re: Muffler mods
« Reply #65 on: March 14, 2019, 10:07:48 PM »
Rule of thumb in muffler mods from my experience is muffler outlet be no larger then  80% of the exhaust port.
Making a living with a saw since age 16.

Offline wild262

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Re: Muffler mods
« Reply #66 on: March 14, 2019, 11:56:35 PM »
Most of the guys that port them for a living say 60%.  At least that's I've always been told.

Offline Air Lad

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Re: Muffler mods
« Reply #67 on: March 15, 2019, 03:18:40 AM »
So I was having a tinker with the 039 muffler while waiting for p & c to arrive
The standard setup must be only 30% if that approx looking by eye only
So I slotted the top 2 holes and bottom 2 holes without going across and up with the bottom lot
Now by eye I would guess 40% to 50% approx
That's a good place to start I thought
Living in town is a consideration
Cheers
Ms 170/260c /039...Husk 142e/240e...Unloved Chinese 51.2cc that hasn't done anything wrong...2 x dead Mculloch's ..Vintage Poulan.. and a vintage Echo that still runs beaut

Offline HolmenTree

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Re: Muffler mods
« Reply #68 on: March 15, 2019, 07:47:30 AM »
Most of the guys that port them for a living say 60%.  At least that's I've always been told.

For a woods ported saw I think 60% is even too much.
I think 40% is max for best power on most saws unless you're running a reed valve, the 80% figure I said earlier is the complete maximum where power is lost.
Making a living with a saw since age 16.

Offline Inaotherlife

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Re: Muffler mods
« Reply #69 on: March 15, 2019, 09:24:20 AM »

(Image hidden from quote, click to view.)
 
Here's my Echo 490 muff mod.
Pretty straight forward. Tossed the highly restrictive deflector, removed screen(but kept in case I want to cut on national forest land), pulled restricter tube and flipped facing out.

It runs and sounds real good. Thumpety-thump. But not too loud.
Removable for other applications?
I'm not sure I am understanding the question.
All three pieces: the deflector, screen, and restrictor tube were bolted onto the outside of the can. I flipped the restrictor tube facing out, instead of in, drilled two holes in the opposite corners, and screwed it down.
I was curious mate because I have thought about a two stage exhaust setup where you can be loud and proud out on acreage but slip in a plate and re tune for urban use.The neighbours may be a little less unimpressed.
Did you're reversing result in any better flow, or raised noise level
Cheers
That saw is only 50cc, and not an overly large exit tube. So not too loud.
But it does have a deeper exhaust note, and feels like it revs freely without sacrificing low end power.
And I also have a 35cc saw with stock exhaust for most of my in town use that's quiet.

Offline mredden

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Re: Muffler mods
« Reply #70 on: March 15, 2019, 11:38:23 AM »
Most of the guys that port them for a living say 60%.  At least that's I've always been told.

For a woods ported saw I think 60% is even too much.
I think 40% is max for best power on most saws unless you're running a reed valve, the 80% figure I said earlier is the complete maximum where power is lost.
Any idea on what percentage is best for cooling purposes? While increased power is not to be sneezed at, my greatest reason for even considering porting is to release the most heat possible when milling with a new 390xp. I live in very warm South Georgia and my new saw ran hotter than I like in February. I'm really dreading July/August and may just forego milling completely during the Dog Days.
I want to maximize cooling while keeping the decibel increase as low as possible. I do some Saturday afternoon milling at home. Neighbors are good folks and I do chainsaw favors for them from time to time, but still . . ..
Intersecting lines on a graph would be helpful. ;D Kidding, of course

Offline HolmenTree

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Re: Muffler mods
« Reply #71 on: March 15, 2019, 01:03:40 PM »
I don't know what's inside a 390XP muffler, if any baffles best to remove them and just enlarge the stock outlet under the deflector.  Experimenting will get it right.
Here I enlarged my MS261CM muffler outlet and enlarged the spark arrestor screen cradle further inside the muffler. Not the neatest job but didn't want the bother removing and reinstalling the deflector cover.
Last pic is when I removed the baffle out of my 066 Magnum.  Its weight surprised me. 


 

 
Making a living with a saw since age 16.

Offline wild262

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Re: Muffler mods
« Reply #72 on: March 16, 2019, 10:52:33 AM »
Most of the guys that port them for a living say 60%.  At least that's I've always been told.

For a woods ported saw I think 60% is even too much.
I think 40% is max for best power on most saws unless you're running a reed valve, the 80% figure I said earlier is the complete maximum where power is lost.
Any idea on what percentage is best for cooling purposes? While increased power is not to be sneezed at, my greatest reason for even considering porting is to release the most heat possible when milling with a new 390xp. I live in very warm South Georgia and my new saw ran hotter than I like in February. I'm really dreading July/August and may just forego milling completely during the Dog Days.
I want to maximize cooling while keeping the decibel increase as low as possible. I do some Saturday afternoon milling at home. Neighbors are good folks and I do chainsaw favors for them from time to time, but still . . ..
Intersecting lines on a graph would be helpful. ;D Kidding, of course


If you plan to do all or most of your milling in the cooler months, that's what I would do.  Keep all the fine sawdust blowed out under your cover/flywheel will go along ways to keeping your saw running cool.  If you must run in warm temps, having a muffler mod "will" lower your cylinder temps. Also maybe have a fan blowing from behind you just to help keep you & the saw cool.   :)

Offline viking59

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Re: Muffler mods
« Reply #73 on: March 20, 2019, 08:59:04 PM »
Preparing my 372 for internal porting, so gave her an "improved" way of breathing better.



 
Kubota MX5200 4WD HST / FEL, Woodmaxx WM-8H Hydraulic Chipper, Everything Attachment 6 ft Hog, Kingkutter 6 ft mower, Howse Disc Harrow. Husky 141, 55R, 372XP


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