Engines timer

i have a suggestion that in the tinker panel that you can modify the time to get to full throtlle/spool up of engines and there is a switch that says automatic when its on it will automatically calculate the time to spool/throttle up so like normal that we have now 2nd:engine timer which means that the time to ignite the fuel so more time=more plumes of fuel like this:
! there is a switch that says automatic when its on it will automatically calculate the time to spool/throttle up
reason why i want it is that because i want to make a merlin engine or raptor