747 V3 TOGA Press Delay

I found some stuff in the AMM that could (I'm not sure, I'm not a mechanic) explain the delay. When you hit TOGA on the ground a so called "stopper test" is performed before the AT engages.

(7) Stopper test
(a) When the airplane is on the ground and the takeoff mode is
selected the master FMC will automatically perform the stopper
test. This test, if passed, will ensure that the throttles
will not retard during the critical takeoff phase. This
critical phase is when the airplane is on the ground with a
ground speed greater than 65 knots and when the airplane is off
the ground and below 400 feet AGL.
(b) This test consists of seven subtests in which one of the
subtests is independent and performed in a different location.
This independent test is known as the secondary throttle hold
test.

... The AMM goes on in detail explaining the specifics of this test. It seems plausible to me that this explains the delay.

I hear it in all the videos. I can even hear it in the PMDG 777. I dont know how they work but could the delay be caused by the servos coming under load moving the throttles? Maybe they are de-clutched from the thrust levers themselves and they "park" at the idle stop. Then when you press TO/GA they move silently from idle until they catch the thrust levers (which are set at ~70%) and then the load of moving the thrust levers causes the whirr sound. Just a thought.

Apparently the system works differently. There is no mechanical declutching. The only thing that happens is that power is removed from the servo.

Honestly, i'd be more interested in correct modeling of VNAV logic, and even simple / basic details like pitching moments due to thrust...

Me too ;-)