Chainsaw Repair
Husqvarna - Stihl - Poulan - Jonsered - Dolmar chainsaws and more => Poulan => Topic started by: doreadeal on September 19, 2013, 11:20:57 pm
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(http://i1111.photobucket.com/albums/h467/adianarion/IMAG0180.jpg)
So I was thinking of making a muffler, just because...out of stainless steel. Figured I'd stick to a canister type and not a tuned type pipe. I'm trying to keep the volume up, with a removable outlet so I can try different restrictions. Started roughing it out tonight. Any thoughts?
(http://i1111.photobucket.com/albums/h467/adianarion/IMAG0179.jpg)
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While contemplating building a new muffler for my 505, I came up with a few insights on the factory compromises and figured I'd share. Feel free to comment, correct and badger...my two stroke knowledge is pretty good but playing with chainsaws isn't my strongest suit.
Ok, so just about all two strokes needs a pretty special exhaust. There are exceptions to the rule, like Detroit diesel, but its mostly fact. The mufflers or tuned pipes actually push the mixture charge back into the cylinder after the initial exhaust pulse. Basically they are designed to take some of the exhaust pulse and reflect it back to do this. The length/time it takes for this effects the range the engine will put power out. If you have ever purchased a dirtbike pipe (aftermarket) they used to specify output, mid range or high end. You kind of can't have both due to how it works.
Ok, that's what I think I know about the general function of a two stroke muffler, now lets look at factory chainsaw mufflers. They are (from what I see) a huge compromise of sound reduction, size and therefore power output. There isn't much tune because of size confines, I'm sure you've all seen how long tuned pipes can be. So they rely on dumping the exhaust into a decent volume. For sound reduction they use a baffle plate, but because its between the actual exit and exhaust port, it has to be damn small compaired to the exhaust port becasue the pulse needs to be reflected back. If they tried to reflect it off the outside of the can, that baffle plate would interfere with it. If you open this baffle hole up too much you lose the reflection pulse.
I'm guessing that if you use the the mufflers exit as a restriction the baffle plate isn't needed at all as long as you don't mind the sound. Also, if you you change the discharge location you probably can have a larger one cause it should have less effect on the return pulse production.
I like the size of the factory mufflers. It works and stays out of the way. That's one of the reasons I'm fabbing one in stainless. Hopefully my thinking is on tract and the end product functions well or better then the factory, excluding the sound reduction. Any thoughts, corrections or insights?
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Neat that you can make that.
Brian Timberwolf sort of done the same thing on a 026 and made the muffler where he could test different size outlets. The info on it is here somewhere too.
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Thread with info http://chainsawrepair.createaforum.com/ported-saws/removing-spark-screens-does-it-make-a-difference/msg15268/#msg15268
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I agree, that is why you see so many outlets on the side. The idea is to vent pressure but keep the reflection.
Echo uses an internal stinger design on some.
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My dirt bike knowledge tells me that you are correct. When I raced you could just look at the expansion chamber and know how the bike would run. The shorter and fatter the stinger the more torqy the engine would run Ala Husqvarna, Maico. Long and skinny the narrower the power band Suzuki/Yamaha.
That is by the way one of my factory provided 400cc race bikes in the picture. It is a 1973 'MJ' close ratio 5 speed bike. ::)
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Do you want me to pull your 505 muffler (you made) post from the one thread and mover here for ya?
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Might be a good idea o guess. Its just the rough shape with no outlet and even some holes blown through the fusing. Welder is giving me issues. Thanks for the replys guys!
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Thanks for the link Cut. Its nice to see I'm not the only one thinking along these lines.
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Should all be merged now.
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anxiously waiting for some results.
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One of the most important functions of a chainsaw muffler is to dissipate heat. Stainless does not dissipate heat very well. On top of that, the material used in producing chainsaw mufflers is VERY thin. Couple thou at best. So the thicker the material, the worst off you actually are. What material thickness are you using?
Kudos to your fabrication skills!!
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Sorry, have been really busy....lots of fabrication jobs popped up. Agreed that stainless holds heat, but really the primary function of exhaust on any engine is exactly that, exhaust. If removal of heat was high on the list they would be aluminum and have fins. True, some engines in history did have fins but far many don't. Plain steel doesn't suck much heat off the powerhead. I would surmise that the added flow itself will remove just as much heat as the steel muffler. I'm not even sure how you would prove it one way or the other, cause the two mufflers will require different tunes, so heat readings won't tell. I just wasn't going through all this work to have it rust out. Ill get a gauge on the stainless tonight and post it. Its a bit thicker then the stock muffler steel. Not much though. Ill grab some pics of the current progress too, which unfortunately isn't far.
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(http://i1111.photobucket.com/albums/h467/adianarion/IMAG0372.jpg)
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(http://i1111.photobucket.com/albums/h467/adianarion/IMAG0370.jpg)
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Seriously, if I had to do it again it would be faster. Not that I've had time to play with it. The way to do this would be the bed the cavity with clay, smoothing the gullies and such. Then spraying expanding foam in it so you had a perfect model. Building a box and then the trial and error stuff is way too time consuming. Of course, if I didn't want max volume it would also have been easier.
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WOW !!!
That thing looks awesome !!
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Thanks. Hopefully now that the schedule is cleared up a bit I can complete it.
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Looks pretty interesting so far. I am curious on how you attached it to the exhaust port. I do not see any screws or bolts.
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Its not yet, I just have the gasket surface. Its actually jigged up in my drill press as we speak. Through bolts like the original with tubes...also like the original. This part is going to be tricky.
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There was 2 different mufflers from oem. 1 split in half and bolted from back half and 1 bolts ran through from front half.
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Really? I've never seen the one that bolts from the back. I'm going with the through bolts on this one. The other style would be easier to make though. You wouldn't happen to have pics of the bolt from the back kind would you? That would have to be real tight and hard to get to.
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Here you go.
Back half bolted on
(http://i59.photobucket.com/albums/g289/doemaster789/PP505PP365JD800/GREEN505011_zpsba8158bb.jpg)
Center baffle I leave out of 2 piece. This is in the ones that is bolted from the front too.
(http://i59.photobucket.com/albums/g289/doemaster789/PP505PP365JD800/GREEN505010_zps979bc0ed.jpg)
(http://i59.photobucket.com/albums/g289/doemaster789/PP505PP365JD800/GREEN505005_zps5e80c968.jpg)
Stock outlet
(http://i59.photobucket.com/albums/g289/doemaster789/PP505PP365JD800/GREEN505008_zpsbc399100.jpg)
Opened
(http://i59.photobucket.com/albums/g289/doemaster789/PP505PP365JD800/GREEN505004_zps0d005038.jpg)
One that bolts from front
(http://i59.photobucket.com/albums/g289/doemaster789/PP505PP365JD800/GREEN505012_zps003ef031.jpg)
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Ah, I see. Its really not too different from the other one. I've probably seen these and didn't realize it was a different box. Cool, thanks.