I originally had the OS 1.20 pumped on my P51. Had too many problems so I removed the pump. It was the older version. Mine is side mounted and has ran without a burp for many years now.

My preference is the 1.20 over a .91. It seems to have that extra power that I need. I love doing slow flybys and then punching the throttle and making it into a victory roll, climb, and split S and the 1.20 has no problem pulling the plane for this maneuver.

It also sounds really cool as it flies by.