Engine Fitting and Cooling Question

But I have a question. Especially about cooling. I can't fit an engine because the car body can't cool specified amount of HP. I know that I need to add some cooling fixtures to do so, the problem is not all grilles and vents add the cooling capacity. Is this a bug or just haven't been coded yet? What are my options besides of adding grilles and vents? I'm fitting a 400 HP engine and I already added so much vents and grilles that my car looks stupid but I haven't reached cooling capacity for 400 HP engine.
Second question, how do I enlarge the engine bay? I wanted to fit a 6.5 L engine but I can't.
Thanks in advanced guys!