I forgot about this reference. I located it again over the weekend. http://www.mazdarotary.net/porting.htm Charlie, you are rigorously correct in that I stated peripheral porting I overuse this term because this is what I read referenced in the rotary aviation use discussions. If this reference is a sound technical reference I see no reason why anyone would want to use peripheral porting in aviation applications. I realize there may be issues I do not yet understand but, engineering a "narrowband" engine does not appear to be useful for my aircraft application (a 4-place taildragger). I suspect the "Extend" port to be a better choice for me yet, the "Mild" may also work. Even with this, I do not care for the slight decrease in torque below 4000 rpm. Has anyone ever seen any of these side ports referenced in aviation applications? I saw Nel's response and looked at the www.rotapower.eu to locate information regarding the PSRU. Unfortunately, I found nothing. I know of Paul Moller and have for several years. He has some good ideas but, I would like to see these come to fruition to a greater degree. The need for funds gets in the way of accomplishments. Rick -- Homepage: http://www.flyrotary.com/ Archive and UnSub: http://mail.lancaironline.net:81/lists/flyrotary/List.html