Ok, not really about EF's, but more so about people trying to BAR JDM motors, which YES, it can be done...

But my question is, why do you have to have the US manifold? Is the bore bigger on the JDM manifold, creating higher air flow? Or what's the difference?

Excuse my ignorance, but that was a question I have never looked into, nor seen discussed...

 

I think the emissions hook ups are in different locations or are missing completely. Since you are barring it as a del sol or whatever it has to have the same manifold or a carb legal one like a Skunk2