The Stihl 25.4cc off of the Pro Series equipment is a great engine. I converted one and had Ken make the parts for me and it spins a MAS 18x6 at 8000 and a Pro Zinger 18x8 at 7000. from what I understand the 27cc is not as powerful as the 25.4cc since it is on the non-Pro Series equipment. I would like to see what you get out of it though.

Almost forgot.
My engine was on a HT 75 pole saw. It is the same engine that is in all of the Pro Series machines though.