11,750 is where the engine is capable of producing the most HP. That doesn’t mean that it is producing max HP on the kart. It probably isn’t because the kart is moving at a pretty good speed and in low gear it probably doesn’t require max HP to make that speed. Idealy you should shift at an RPM that puts you at 11,750 after you go into high gear. At that point your in a lower gear and the kart is accelerating so the engine is fully loaded and producing all the HP it’s capable of at that RPM. It may not be possible to get to a high enough RPM to be at 11,750 after going into high gear so you probably want to shift at the higest RPM you can to come as close as possible. I had a DD2 and shifted around 13,000.