Chainsaw Repair

So i stole an idea from someone else and used Sketchup to calculate the area of all the openings.

Anyways.  The black rectangle represents the "ideal" opening of the exhaust and is based on the commonly accepted 80% of the exhaust outlet (outside-cylinder) and ~150% of the exhaust outlet (in-cylinder) rule of thumb

As you can see with my existing modified exhaust hole, i can almost double the size and be within the rule of thumb specs.  I think i will try it 'as is' and see how it goes and then open it up further based on those results.

There was an interesting post on another site where a guy did 5 successive exhaust mods on a 260 and analyzed the results in terms of engine/exhaust temp and sound level. He started with the muffler that had the single 1/4 inch hole and then opened it up sequentially to be a 1.5 inch x 3/8 rectangle... which is basically the same dimensions of the "ideal" rectangle in my pic.

G