If you don't need full thrust for take-off then just use two engines (lower noise?), and pull your other two out at altitude.
Are you a pilot?
If you fly jets you would know that you're not saving fuel by shutting down engines in flight. Think of the drag generated by huge wind milling fans....like unfeathered, wind milling propellers.
Ever wonder why the British Airways B747-436 with an engine failure after take off at LAX didn't reach destination LHR? . . . Because of excess fuel burn on 3 engines!
