At 21:00 minutes into the video David does a very good job explaining. He did a good job and once and for all putting an end to all the mystery. Yes, if you want maximum performance you will need to put in 91. If you us 87 you will not get the performance, but it will not damage your engine. Before you add comments, please look up the pedigree of David, his engineering background and his direct contact to the Tahra Plant.