Brian, quite simply, you get char from lots of heat, ideally, a pre-heated stone (or steel) hearth and intense top heat from a broiler element or from a bottom heat source that uses deflectors to redirect the heat to the top of the pizza. Is this NY Style pizza you're trying to make? You can't make NY Style pizza in a 400 deg. oven. You get a little bit of leeway temperature-wise depending on the materials you bake it on, but I would say 500 is the bare minimum, although, the higher the better.
What model oven is this? Is there any documentation for it online? Do you have a manual for it? Is it convection? What's the peak temp?