You have the right idea searching the forum. All the info is already out there. To restate, most guys cut out the inner baffle so that you can see straight into the cylinder. If you can, take a hike over to your local Stihl dealer and get the dual port cover for the older 066s. I think the part number is 1122 140 0800. (I recall the part number being given in one of the posts.) The factory cover looks nicer than cutting holes.
For kicks, Ken Dunn (kdhotsaw) posted this:
"The muffler work that we do to the 066 muffler to increase the power is as follows; go inside and cut the end out of the stainless steel perforated box at the exhaust inlet, match the exhaust entry and gasket to the barrel opening, and on the 066 go to your local stihl dealer and buy the ported cover for the 066 magnum muffler. its 31.00 dollars and has a screen and deflector over the port. this will add 15-20 % to the power level. you can also cut a port in your existing cover, if you do make the port 1 1/2 long by 7/16 tall"
The thread entitled '066 Stihl"Nowhere to go" for woods saw modification?' has it all.
Good luck, Chris B.
