Chainsaw Repair

Not on here.

Corrected for altitude that's about 158 for compression.

Raising the exhaust port will reduce the compression a little. But altitude has a big effect.

Yes, the Hyway cylinder exhaust ports are already about as high as you dare go.  AFAIK the higher ports are like a long duration cam in  four stroke and reduce your over all volumetric change. Therefore the compression is reduced.

To minimize the squish, and also to widen the squish band, and/or even pop-up the piston overcomes any compression loss due to increased timing.

Naturally you already knew all this and I'm just running off at the jaw being a troll.

The typical big problem I've seen on aftermarket cylinders is the shape of the top of the exhaust port (The Arc) and the lack of beveling on the top of both the intake and exhaust ports tends to score the top corner of the piston crown and the wear the edge from the top of the ring.

Hyway has been better at this than the other brands.

A ring with a rounded top edge at any of the ports will still give decent static compression but the power will be diminished.

Kevin had a 272 with a AM cylinder come in with 150 pounds of compression but ran like it was four stroking until it was too lean to run. The ring top was round at the transfers. A new ring and all was forgiven. 

Usually a few degrees isn't that much difference.