Engine cover is no problem with a hex tool. You have to remove a little plastic piece from the stock harness. From there plug and play. Put the unit somewhere out of the way with a zip tie. I put my unit somewhere I could easily adjust it.
I tried 100% and got codes. Dropped it down 5% or so per run, until no more codes. I"m guessing that was about 85%. Mine is off the car now for the winter. Figure I don't need extra torque in the snow.