Chainsaw Repair

I have several Poulan 295's , 46cc chainsaws that I have worked on.
First I have removed the metal piece or heat shield in the exhaust and then widened the exhaust port to eliminate the step.
Like 660 said I would not raise or lower the exhaust port opening.   
On the stock muffler I usually weld the back holes up and then make a new one on the clutch side.
I then cut away about half of the center of the baffle out and leave the spark arrestor in place.
I have done plenty of cutting and with the mods and have had no problems.   
Also when ever I grind on a port I either sand the edge smooth or bevel it just a little to prevent the ring from hanging up on it.

I did bump up the compression on one but it was done in a rather unconventional method and so I will not go into that.
Like 660 said you should look for mods that give torque but not RPM.