Hi, I am looking to buy a 2006 Jeep Grand Cherokee Overland 5.7L V8 4X4. Do I need to add an Air Intake to it for more power or will it have enough with the V8 alone. My jeep that I have now is a 1998 JGC Laredo.
For the most part, unless you go racing all the time, a Cold Air Intake is a waste of $$$. Some actually pull in hot engine compartment air instead of cold air. At best, most of them just make more cool sounding noise, but do nothing for normal driving.
You can make your stock one more than adequate by adding a good aftermarket air filter (K and N or TrueFlow), and a second air intake tube that runs from the bottom of the airbox (remove the drain cup) to behind the grill. Be sure to punch a little hole at the lowest point of the tube for drain purposes. Here's a pix of what it looks like.
Aftermarket intakes, and catbacks just empty your wallet, make it drive worse than stock, and all the added noise they make gets old real quick. Save your cash for all the maintenance and fixes that the 2006 is going to need before any power adders. You would not believe the list of repairs from my 06 Overland. FWIW I've examined a K and N under the microscope (I'm a Distributor for optical, electron and atomic force scopes), and compared to a stock paper filter, the holes are huge and let much larger particles through to the combustion chamber. This is how more airflow is achieved, which is not worth the long term damage.
You can indeed make the hemi much more responsive with the right add ons. First thing to do is spend $100 on a catch can and clean the throttle body, or even better, get a Modern Muscle 85 mm taper ported TB. Then go with a CMR custom tune, Diablosport Intune is great for this.
JEEP ADDICT, that is a stock 5.7 airbox with the drain cup removed and a 3 in. aluminum flex duct attached to it. You route the flex duct to somewhere behind the grill so it pulls in nothing but ambient air. Also, leave the stock inlet in place. Then, if you want, add an aftermarket filter element, or keep the stock one. Like dmsfun says, the K and N's are fairly coarse, and work better when they've accumulated a little crud. Not the best, but also not the worst. Another one which, IMO, is better than the K and N is the Trueflow. I have a K and N on my WK and a Trueflow on my LX. I've also run the stock elements from time to time and really don't see any "seat of the pants" difference. Just change the stock type at regular intervals. The "high efficiency ones" don't require service quite as often.