Don't know about the ARC airbox. The ECU adjusts fuel according to sensored air (in closed loop mode) so unless it becomes a restriction I don't think bigger is better.

 

Does your airbox has the AFM sensor installed to it as well?

Yes, on both the stock & ARC box. Essentially this guy built an airbox that took up almost every available area within the engine bay. He had a version one that he later improved upon. With each increase, his air/fuel ratios would lean out I think, and he would head back to the dyno to correct. Heat was an issue of course. Interesting anyway.

 

I think ideally the ARC box is meant to have a little bonnet scoop thing, but I won't bother with that.