Chainsaw Repair

He is wanting to put a 395 p in a 2100. 

Anything gained in the windows of 395 compared to that thick ring 2100 p in ebay pics?

There is a reason why Husky went from the original full skirt windowed piston to the most current bridged pin support piston found in the 272/288/394/395. They dabbled with other windowed piston designs like in the 2100 but as everyone knows they didn't have the same performance as the large windowed piston. The problem lies with the stock lower transfers. They majority of the flow has to go through the piston windows as the full skirt closes off the transfer when getting closer to BDC, effectively neutering the time area of the transfers. So the large window was the ticket. Now when you remove the full skirt and keep the piston pin supports high on the piston, like the 395, it never impeads the flow into the transfers and you get to utilize much more of the time area that the transfers are open. 

Also when going to a 395 piston you can open up the lowers much more creating a larger funnel which can be done in a way to guide the charge into the cylinder better. In my opinion you are able to raise the usable RPM range this way without sacrificing any peak torque because you can stick with larger blowdown numbers, the loop scavenging is more efficient, and there is enough flow to keep the engine from chocking out until a higher RPM.

Another improvement in the 395 piston is ring pin location above the intake port. I'd prefer the skirt length of the 394 piston as it would help keep the intake duration under control but the pin locations on the 394 pistons are horrible being right over the side of the skirt, so you are really limited to your transfer shape or you have to run it backwards and keep the exhaust port smaller. 

I think in the saw that I posted before I just skimmed the base of the cylinder to make sure it was flat and I took 0.010" out of the squish to get the 395 piston to swing.  Which put the intake duration at 157 degrees without touching the port.