best AFR for Power??

Not sure on where you have the sensor mounted. Mines on the left side 3” exhaust pipe about a foot from the collector flange. Get good readings but tried using it on a collector for at the strip and couldn’t get accurate readings (showed way lean) likely because I drilled and welded the bung too close to the end I guess. So I just use MPH for getting the jetting right at the track. The ratio number (if sensor was mounted correctly) would be whatever it would be. MPH would be the better number obviously.