Echo cs-355t
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    Jim Timber's Avatar
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    Echo cs-355t

    Yesterday I got this little guy on one of the 20% off sales events Echo has when their dealers have an "open house" event. $300 out the door was too much temptation to resist. Quite literally half the cost of the next most desirable arborist saw in this size; the Stihl MS201T. Frankly, I don't need another $700 chainsaw, and this is a "luxury" item for me right now. I wouldn't have even gotten it had I not sold off a couple other pieces of OPE my sister and BIL gave me. Thanks sis!

    True to form, I immediately ripped out the carb limiters and disabled them; because you cannot tune a saw without being able to make it bog down. Sorry EPA, you failed.

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    Then like every red blooded American, I proceeded to modify it to make more power. Echo uses these little two-piece stamped port covers on lots of their equipment, and it makes it really easy to open up the exhaust outlet without actually cutting anything on the saw. I modified the original on my other 34cc Echo, but this time I decided to start from scratch.

    Click image for larger version.

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    Once that was cut out, I transferred over the port dimensions and went over to my short materials rack and found a desirable piece of tubing and whipped up a deflector with a bit more breathing room.

    Click image for larger version.

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    Then the last bit of the fabrication was to slightly enlarge the opening in the muffler shield so the metal wouldn't touch the plastic.

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    It's currently drying, having been sprayed with a coat of high temp flat black BBQ paint.

    What sucks is that we're supposed to get nothing but rain for the next 2-3 days, and I have trees that need pruning with this little guy.

    Some guys advance the timing on these too, but I don't know if the gains are desirable for my uses. It adds some top end, but at the expense of torque. I think I'd rather have the torque.
    glc, Gizmo2, jdmich and 1 others like this.
    5065E MFWD w/553 loader

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    AJgrn78's Avatar
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    Quote Originally Posted by Jim Timber View Post
    Yesterday I got this little guy on one of the 20% off sales events Echo has when their dealers have an "open house" event. $300 out the door was too much temptation to resist. Quite literally half the cost of the next most desirable arborist saw in this size; the Stihl MS201T. Frankly, I don't need another $700 chainsaw, and this is a "luxury" item for me right now. I wouldn't have even gotten it had I not sold off a couple other pieces of OPE my sister and BIL gave me. Thanks sis!

    True to form, I immediately ripped out the carb limiters and disabled them; because you cannot tune a saw without being able to make it bog down. Sorry EPA, you failed.

    Click image for larger version.

Name:	20170519_191628-1.jpg
Views:	4
Size:	408.7 KB
ID:	371297

    Then like every red blooded American, I proceeded to modify it to make more power. Echo uses these little two-piece stamped port covers on lots of their equipment, and it makes it really easy to open up the exhaust outlet without actually cutting anything on the saw. I modified the original on my other 34cc Echo, but this time I decided to start from scratch.

    Click image for larger version.

Name:	20170520_012719-1.jpg
Views:	3
Size:	404.1 KB
ID:	371305

    Once that was cut out, I transferred over the port dimensions and went over to my short materials rack and found a desirable piece of tubing and whipped up a deflector with a bit more breathing room.

    Click image for larger version.

Name:	20170520_024908-1.jpg
Views:	3
Size:	478.9 KB
ID:	371313

    Then the last bit of the fabrication was to slightly enlarge the opening in the muffler shield so the metal wouldn't touch the plastic.

    Click image for larger version.

Name:	20170520_024858-1.jpg
Views:	3
Size:	438.5 KB
ID:	371321

    It's currently drying, having been sprayed with a coat of high temp flat black BBQ paint.

    What sucks is that we're supposed to get nothing but rain for the next 2-3 days, and I have trees that need pruning with this little guy.

    Some guys advance the timing on these too, but I don't know if the gains are desirable for my uses. It adds some top end, but at the expense of torque. I think I'd rather have the torque.
    Is that modification to the exhaust really going to result in a significant power gain?

    If there's one thing I've learned from tinkering with 2-strokes, it's that they can run like s--t if they don't have the right exhaust back-pressure. Another thing I've learned is that loud exhaust really makes your perception of power "biased"

    Maybe you've had better luck with DIY exhaust tuning than I have, if you can tell a measurable power gain that's awesome!
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    Jim Timber's Avatar
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    The outlet area has a drastic impact on the engine's ability to breathe. Not enough backpressure can kill the torque of a 2 stroke, that's for sure. Increased volume is not a desirable outcome for me, so this has nothing to do with making more noise.

    It's been established that a muffler mod on this saw is good for about 10% more power in the cut, but it also makes the saw run cooler and rev quicker, and those are very desirable qualities in themselves. The extra speed in the cut is always nice too.


    As for being able to tell on this saw? I never put it in wood before modding it. It was very noticeable on my cs-352 when I took the catalytic converter out of that muffler and went to a round exhaust port. My first outlet mod on the 352 was not successful. It was insanely loud and reduced the backpressure too much and the saw fell on it's face. I fixed that with a more restrictive outlet and now it's a "screamer" (cuts great!), but it's not loud.

    The way I designed the pipe outlet and it's relationship to the mounting flange causes turbulence as the exhaust exits the pipe. There's also not a straight path to atmosphere for the exhaust pulse coming out of the engine, and that helps a lot with sound mitigation.
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    AJgrn78's Avatar
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    Quote Originally Posted by Jim Timber View Post
    The outlet area has a drastic impact on the engine's ability to breathe. Not enough backpressure can kill the torque of a 2 stroke, that's for sure. Increased volume is not a desirable outcome for me, so this has nothing to do with making more noise.

    It's been established that a muffler mod on this saw is good for about 10% more power in the cut, but it also makes the saw run cooler and rev quicker, and those are very desirable qualities in themselves. The extra speed in the cut is always nice too.


    As for being able to tell on this saw? I never put it in wood before modding it. It was very noticeable on my cs-352 when I took the catalytic converter out of that muffler and went to a round exhaust port. My first outlet mod on the 352 was not successful. It was insanely loud and reduced the backpressure too much and the saw fell on it's face. I fixed that with a more restrictive outlet and now it's a "screamer" (cuts great!), but it's not loud.

    The way I designed the pipe outlet and it's relationship to the mounting flange causes turbulence as the exhaust exits the pipe. There's also not a straight path to atmosphere for the exhaust pulse coming out of the engine, and that helps a lot with sound mitigation.
    All of my saws are at least 30 years old so exhaust mods have never been a consideration

    I do however have an old "Canadien" saw, must be 1960's or older, that runs and is complete except for the muffler, was my grandfather's. I'm not sure how but I'd love to find, modify, or make a muffler for it.
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    Jim Timber's Avatar
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    Technology has come a long way since the mid-80's. Those old saws were built to last though, and no EPA nonsense to defeat either.
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    AJgrn78's Avatar
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    I run old McCullochs, sometimes it's hard to find parts but I have countless hours on them and they still run strong.

    When they finally die I'll hang them on the wall and get something shiny and new.
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    Jim Timber's Avatar
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    I've got 2 80cc Mac's from the 70's that don't run which will be man-cave art when I finally get a man-cave.

    Cool old saws!
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    Quote Originally Posted by AJgrn78 View Post
    Is that modification to the exhaust really going to result in a significant power gain?

    If there's one thing I've learned from tinkering with 2-strokes, it's that they can run like s--t if they don't have the right exhaust back-pressure. Another thing I've learned is that loud exhaust really makes your perception of power "biased"

    Maybe you've had better luck with DIY exhaust tuning than I have, if you can tell a measurable power gain that's awesome!
    i hate the term "back pressure" the last thing you want is exhaust backing up in the cylinders you do need a properly designed exhaust to make a pulse in the exhaust to pull more spent gasses out of the cylinder in the very little time that the exhaust is open called scavenging .

    but when the engine spins 10k plus rpm bigger is better you really dont want much restriction. that exhaust just needs to get out at that speed
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    Jim Timber's Avatar
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    Dynamically speaking, it is back (low) pressure though, which is caused by an area of high pressure ahead of it. If it wasn't beneficial, we'd still be running open mufflers like in the 70's. You need to isolate the pulse(s) so that you end up with a low pressure zone at the exhaust port, ideally whenever it's most beneficial between the transition from scavenging to the dynamic impulse from the transfers. We can't all run tuned exhausts (not enough room!), so we have to make do with the enclosed space of a muffler to keep the velocity up. Do it wrong and you suck your intake charge out the exhaust without burning it first or you lose that scavenging and the saw performs badly; and if you choke it down you just can't pump the fuel through to make any power and the RPMs won't climb. It's all about keeping the exhaust charge velocity where it needs to be.

    The muffler on a 250-1 Mac is nothing but a tube with a grate drilled into the end of it to keep things from crawling up into the exhaust. Those saws can't pull more than about 6000rpm. My 71cc saw would kill it in a speed test - it runs 9600 in the wood.

    Tuned 2-stroke exhausts are a thing of beauty from an engineering standpoint. Lots of applied physics going on in that stupid looking buldged tube.
    Last edited by Jim Timber; 05-22-2017 at 06:06 AM.
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    AJgrn78's Avatar
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    Yep... I have a few 2-stroke machines with high performance exhaust, the outlets (stingers) are a fraction of the size of the exhaust ports, and they have the big fat expansion chambers. And they rip! Wide open exhaust on a 2-stroke is never good at any RPM. I remember guys talking about the old snowmobiles with the wide open "megaphone" exhaust pipes, loud as hell but ran like crap.
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