Rotate an explosion

I followed a tutorial at blenderguru about making explosion, and now I want to rotate it on it’s side while still keeping the particles going the same way, how can I do this?

Hmmm, I haven’t done smoke simulations for a while. AFAIK, gravity will always take the global Z axis as a reference. Maybe you can get away simply rotating the camera 90º on its local Z axis, rendering your explosion and then compositing it into your final scene. Just an idea.