"The Split-Ess is primarily a defensive move, unless you are attacking with considerable altitude and are meeting your target with a nose to nose heading. Then you would let him pass beneath you and you can Split-Ess onto his tail for the shot."
"The Split-Ess requires that you roll 180 degrees first, then pull the stick toward you. Be careful not to roll your aircraft in the pull. You will pass the + symbol which means you are pointed straight down 90 degrees. Continue pulling through this + symbol monitoring speed and if necessary reducing power in the dive portion of the Split-Ess. Continue pulling until you level out in the opposite direction."
To ensure that you are doing these correctly do them over a runway, or simply mark your compass when you begin and end your Split-Ess. It should move 180 degrees from, for example, due west 270 to due east 090. Variations on the Split-Ess can be had with an additional roll when you pass 090 degrees at the + symbol. Roll 90 degrees to throw off your opponent and come out at a new heading. A roll effected while you are pointed straight down will be the most efficient for an escape maneuver."