K&n's, tip lowboys whatever u use will suck in warm air from the engine, but that doesnt mean u dont have to use them, the tpi valves will give u 3 extra hp on top end thats the only point in time where whatever you use, it will not suck in warm air cause u have a constant flow of air coming underneath your hood, i have them on my 500ss and i noticed alittle more top end mph.