Chainsaw Repair

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?

Thread with info   http://chainsawrepair.createaforum.com/ported-saws/removing-spark-screens-does-it-make-a-difference/msg15268/#msg15268

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. 

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!

Should all be merged now.