V1 can never be below VMCG. If your TOW V1 is below VMCG, you adjust it to the VMCG value.
VMCG= minimum control speed on ground=rudder authority.
On a Classic 747, VMCG flaps 20 @ 320,000kg TOW is 142KN and so is the V1. At 340,000KG TOW, flap 20 V1 is 147KN with RB211-524-D4 engines. Sorry no data for 744, they do not need flight engineers.
