I just upgraded my 4.7 L from the stock Intake Manifold to a Mopar H.O. Intake Manifold. It was a quick and inexpensive HP jump. The company I bought it from quoted a 15 to 20 HP increase at the wheels. Normally I would be a little weary of taking that number at face value. But, after the install I can feel a real difference around the 3000 rpm range even with the 20 inchers.