I work on several IO-520's + IO-550's, some turbocharged, some not. I also

know the service bulletin and have the calibrated orifice tool. it's

interesting that you CAN get 76/80 on a good engine, so why is 50/80

acceptible? I also have noted that most of the engines start out with good

compression readings and fall off quickly within ~200-500hrs, including a

Victor Black Max.