Keyword here is "Cold Air" intake, K&N, Volant, Injen, AEM, Ractive somehow do not make one, maybe if someone convinced AEM or Injen to make one they'd be best.

Cold Air Intake System is the cheapest and best bang for the buck to gain HP

Proven that in order to produce more HP you need cool air, all I have found so far are kits with filters mounted in engine compartment and the heat produced by our engine is so intense that all that is being sucked in is hot air.
You simply have to look at auto racing, mastered in F1 (which technology is more closer matched to our type engine) drivers are constantly looking for clean air for maximum engine output and perfomance, thus there should be no gain and possible loss of power using those in engine bay suck in hot air.

K&N are good product over stock, however very mnimal gain power wise and maybe .5 MPG gain.

Look in threads I think someone made one that sits behind grill.