Manual says 91. Running 93 in my wifes and seems to run very well. Have one other that tried 87 in and does not do well, runs but takes longer to warm up and runs rough. Had only put in about one gallon so topped of with a couple more gallons of 93 to bring up the octane level and made a huge differance, much smother, almost no warm up, and big differance in performance. Hope that helps.