I am modelling an intake plenum (manifold) for FSAE, It has one Inlet and 4 outlets corresponding to 4 cylinders.

So far I have set up each outlet port to have a pressure based boundary condition that is time dependant, and done basically everyhting in this video http://www.youtube.com/watch?v=vi8I4-Rpwio

I don't understand why the pressure is being set at atmospheric pressure when the cylinder is supposed to be "closed". If both the inlet and three non firing cylinders are set at atmospheric pressure and one is set below atmospheric (firing cylinder) wouldn't all other inlets be pushing air into the plenum?

I actually ran mine and this is what happens. I get four inlets and one outlet basically. How can I prevent this? is there a way to define it to not flow backwards?

I have been successful in getting a transient flow animation for the time frame I want its just that I get flow coming into the plenum from the other three boundaries (cylinders) when they should effectively be closed.

I understand why this happens, it makes sense, but I don't know how to go about getting the results I want. Can anyone suggest what I could do?

There is an excel sheet attatched below that I used, as well as a video of my results for the animation, as you can see my firing order is set to 1-3-4-2 (1-4 from left to right in the video) and you can see that the outlets with highest velocity change in that order. But you can also see that the other outlets are actually having air flow through them aswell.