chainsaw engine mods

[VTMechEng]

I have noticed a lot of people here doing mods to their chainsaw mufflers. Being the dorky engineer type I started to research the subject and what I foud was interesting... It would seem that how a muffler is designed on 2 strokers has a much greater impact then on a 4 stroke. The 2 stroke requires certain design characteristics to create the required backpressure and "pressure wave". I think we all know what backpressure is but the pressure wave is a energy wave directed back toward the cyclinder in order to port plug any escaping intake charge. I have always been a Tim Allan type, ugggg more power, but I would hate to ruin a perfectly good saw. Just some food for thought and in no way a criticism to anyone moding their toys, God knows I have done plenty of them in my day.

 

[SIRCHOPALOT]

what you are speaking of is an expansion chamber, not a muffler. an expansion chamber has is made up of several cones and has what is called a divergant cone at the end. the divergant cone is set up a specific distance from the piston face to bounce the sound wave back to the exahst port. it all works on the speed of sound.of course there are many variables such as port timing and volumes that affect how you set it up, but the basic thing is exh port timing and the speed of sound. on the other hand the mufflers that you are reffering to are just that. all they do is make the motor quieter. there is no performance gain with a muffler. you just need about 85% of the exh port area for the vent. the epa makes the manufacture meet certain emission specs, and one way they do that is to put a smaller vent in the muffler, allowing them to run it leaner.

 

[VTMechEng]

Thank you for the information...I am not above admitting I don't know everything, just learning as I go. Any info is good to learn. So what you are telling me is the muffler on our chainsaws can be opened up as long as the output hole stays at 85% that of the exahust port?

 

[SIRCHOPALOT]

that is correct 85% of the exh port opening. you will probably need to richen up the high speed screw on the carb also, about 1/4 turn. if not the saw will be too lean.