Well, maybe the moderators can sticky this thread, or something - I hope it can grow into a good bit of information, sort of like a reference guide, that folks can use to find info on modding their mufflers, rather than seeing a new post in the forum every other day.
YOU NEED TO MOD YOUR MUFFLER!
See this-->
http://www.palmtreeservices.com.au/video/33cchomelite.wmv
A basic muffler mod "opens up" the exhaust system to allow more gasses to flow out of the engine with less restriction. This is accomplished with a bigger 'hole' in the muffler.
SO, What do you need to mod your muffler? A little time, a little patience, a few tools, and a little skill.
You will need the following tools:
Drill and drill bits - up to 1/2" for most smaller saws, up to 3/4" for bigger saws.
A welder (MIG/TIG) or a set of Oxy/Act torches and proper filler material - yours or access to your friends, it doesn't matter, but you shouldn't be trying to JB weld your muffler together!
Dremel tool/files/die grinder - Just something to clean up the burrs on your steel pieces.
Hacksaw and tin snips - depending on the style of mod you plan to do, these will come in handy and at times, be necessary.
An assortment of steel - 1/2" - 3/4" tube, 18 ga. sheet, spark arrestor screen.
Mods are accomplished MANY different ways. But, the most basic modification is to drill a hole in your muffler. This increases the area your exhaust has to exit the muffler - allowing the saw to breathe better, run cooler, and perform better. Holes should be drilled in a convenient location where the exhaust won't blow back at the saw operator, burn plastic pieces on the saw, start a forest fire, etc. "Measure twice, cut once" and make sure you know what you want before you start hacking away at your muffler. The surface area of the new exhaust hole should be about 80 - 85% of the exhaust port surface area at the cylinder. Taking your muffler too far, and making too big an exhaust hole will actually decrease your saws performance!
Some saws have a 2 piece muffler. These can be disassembled and the baffles inside can be modified or removed. Some Stihl saws can also be equipped with a factory dual port muffler cover which usually makes any additional muffler mods unecessary for most folks. Saws without a 2 piece muffler cover can be cut open and gutted - however this is rather involved and requires more skill to put them back together (best accomplished with a TIG welder).
After you have your holes drilled and baffles modified, you need to "finish" your muffler. Finishing it can be accomplished many ways - the "looks" of the mod should be pleasing to you, but the bottom line is, the muffler MUST function well to give the desired performance. ALWAYS install a spark arrestor screen over the new hole you have drilled in your muffler! Based on how far you have taken your muffler, it's initial design, and your patience/craftsmanship skills, will determine how you finish it. I have included some picture of muffler mods below.
Some folks drill a hole, and use a washer with a screen behind it, welded to the muffler to "finish" it as seen below on rahtreelimbs Husky 359.
On a muffler mod I did to my Shidaiwa 577, I removed the factory deflector, and fabricated a new one out of 18ga sheetmetal, and 1/2" tube. My new piece replaces the factory deflector, is bolted to the muffler, and has a spark arrestor screen behind it. The internal baffles in the factory muffler were very free flowing, and I did not have to modify them.
I encourage others to add pertinent information and pictures to this thread with descriptions of their work, what saw it was on, etc. Please do not use this thread for ****-chat.
