There wouldn't be any restriction. Unless you're taking about further down into the head where I wouldnt be doing any adding. Just picture the splitter coming strait up to the intake port opening. That is the only adding that would be done. I will have to get pictures for you to fully understand.
In theory as the engine speed is increasing, sucking in more air, it will be assisted by the increase in pressure created from the venturi which is what it is intended to do. As for restricting flow, it would be no worse than the already too small stock oval ports.
