heel-and-toe without double clutching does nothing for the gear box synchros. You need to let out the clutch before you blip the throttle so the input shaft and output shaft are at a similar rev. that way when you jam that gear in, the synchros do less work for the dogs to engage. and FYI, alot of people just use the side of their feet to blip the throttle while half their right foot is on the brake. feels much more natural than having your foot sideways :D there is a particular rythm and timing to it. Brake, clutch, neutral, clutch out, blip the throttle (knowing how long takes practice), clutch, downshift, clutch out and back on throttle. you want to time it so that when you are ready to get back on the throttle you have just come out of the corner. it's all about being in the right rev entering the turn.