On the navball, on the thrust meter, there's a little red section. It's always ticked me off that it sits there and doesn't do anything so here's my idea. If you increase thrust using the shift key then it automatically maxes at 100% (same if you use the Z key), and you press shift (or Z) again to get increased thrust. BUT if you do this your engine will overheat and explode if left for long enough, just to keep it balanced. :D