With the corolla manifold: After looking at some pictures it seems that the manifold will need to be modified, the "flange" part will need to be cut off, and then the part before it splits into four runners (the "ball" sort of shape thing) will need cutting back, the flange thing will need to be bored out to a bigger size and then welded back onto the manifold to allow for the bigger size throttle body. So basically even if you put a bigger throttle body on there it's still choked by the inlet of the inlet manifold. So needs a bit of custom work. But it looks to me like it's the most air you'll be able to get in there without upgrading to ITB's or forced induction or some sort of custom setup. Although I could be talking out my arse, someone please correct me if I am. (I know my explanation isn't exactly as technical as it could be).