Originally Posted by tbzep

It is a stable rocket so you could stuff a pretty big and heavy motor back there and be fine. Your configuration won't weigh as much as a full G motor. Four full 20Ns D's are equivalent to a full 80Ns F in impulse. The Quest D16's are a little under 13Ns so you are looking at the equivalent impulse of a 50Ns F motor.

The total weight of your four Quest D16's are 102g. An average G motor probably weighs about 150g. A full reloadable G will be considerably more. However, if you don't feel comfortable with it, sim it in OpenRocket (free) or ask a member with RockSim to do it. They can figure in the motor mount differences too.