Stihl piston in a Dolmar PS341?

[hector]

I can put a 37mm piston from Stihl to a Dolmar PS 341? Stihl's piston has two rings. I don't want to spend money without knowing if you will improve performance. or any piston that can put to increase compression

 

[J D]

Unlikely... & 2 rings probably wouldn't make a significant difference anyway.
If you just want more compression measure squish & reduce/ delete the gasket as appropriate (assuming there's not another cause for low compression)
A muffler mod & tune is a cheap & easy way to get a good boost too.