4. And air intake won't increase your gas mileage at all. If anything, it'll lessen it. The engine is receiving more air, and therefore uses more gas, at least under load. The stock intake is really best for mileage and fuel efficiency. AEM makes good, inexpensive intakes, but this will increase your engine's efficiency, and not fuel efficiency. There's also
this nifty thing. There's a couple for different models. They create a low-pressure in their plenum so the engine can more easily suck air, and there's also a "reserve" when you first hit the gas, because it acts like the intake manifold plenum. I'm not too sure that part works though. That's what I heard.