Larry That engine was originally designed to be a 20 degree V6 so that manufacturing costs could be significantly reduced by only having to make one head for a V6. The idea originated from the Volvo 5 cylinder which is cut from a block of cast aluminum. It also simplifies the intake system due to the centrally mounted plenum and injection rails which was nearly impossible to get right when using earlier carb systems. That engine costs no more to produce than a double overhead cam 4 cyl, but with 6 cyl output. They may have changed it to 15 degrees to dampen more of the vibrations associated with either a 4 cyl up and down or V engine rotating mass that is not matched balanced like a V8 (issues that they have with 90 degree V6 but don't in 60 degree V6).
Cool design though I don't know how practical for plane due to the need for computer to make it most effective... Colin & Beverly Rainey Apex Lending, Inc. 407-323-6960 (p) 407-557-3260 (f) www.eloan2004cr.com crai...@apexlending.com