I would think you'd want it pretty close to the exhaust manifold, but one question, are you just going to vent the exhaust right out into the air from there? If so, you might want to get it a little lower or something. Otherwise I think you're going to be pouring exhaust fumes right into the passenger compartment of the car, I'm not sure where it draws air in, but I know when you have an exhaust leak in that part of the exhaust, it POURS into the cabin. I have near fatal experience with this, my girlfriend almost died, ok maybe not died, but she was throwing up all over, couldn't maintain a wakeful state, and we almost had to take her to the hospital. This was interstate driving too, not slowly around town. So PLEASE think about that fact when you're putting it in. Not to mention having that exhaust all the way up there, might funnel alot of heat and exhaust right into the engine bay too. Maybe right in front of the cat would be better?