steady and unsteady conditions
 

Iam simulating a twin cylinder diesel engine manifold.I set the unsteady boundary conditions for two outlets. Means some time one out let is open and another one is close.

Now my question are
1)Is it nessary to run the steady simulation for this problem.Can i directly not run the unsteady simulation.

2)If i run the steady state simulation can i take the pressure 0 for one outlet for sometime (means when the respective out let is open) and 0 for another outlet for sometime OR i set pressure 0 for two outlets at a time.
please give me suggations in this matter.
Thanks in advance.