's give the engine colder air, which colder air has denser air in terms of oxygen, more oxygen going into the engine means more combustion, which then equals more hp...And yeah i agree as well, Injen
gives more higher end RPM, and AEM
gives more lower end RPM, its your choice, but i recommend, Injen
for GT Manuals and AEM
for GT/GTS Auto and Gts Manual..