GenRight Hood Louvers from 4WD.com. They have several other styles to choose from.
1 hour of time
blanket or tarp to cover engine bay
STEP 1 - Tape off area where you want to mount louvers: Use blue painters tape to tape off the general area where you will be putting your louvers. This will help prevent any damage to the edges of the area you cut with the grinder wheel. Depending on how many louvers you get, and the size, you'll have to pick flat spots on the hood. We decided to mount ours closer to the center and closer to the windshield.
STEP 2 - Use a sharpie to trace and mark off louvers: Using a measuring tape, place the louvers on the hood at an equal distance from the center of hood. You'll want to be as precise as possible here so that the finished product will look good. When you have determined where the louvers will be, trace around them on the tape. This WILL NOT be the area you cut, but rather where the edges of the louvers will sit. Leave about an inch to two inches around the edge for the rivets and draw another smaller rectangle inside. This will be the area you will cut.
STEP 3 - Protect engine bay with tarp and make cuts: Open up the hood and place down a tarp or other fire-proof blanket. The last thing you want is sparks flying into the engine bay and igniting anything. It is also a good idea to remove the factory Jeep hood insulator that mounts underneath the hood. You'll have to cut this later to allow airflow, but remove it for now to prevent any damage. Using a cutting wheel, carefully cut along the smaller rectangle you marked off on the tape.
STEP 4 - Remove tape and file edges of cut: After you make the cuts for the louvers, remove the tape. Use a file to remove the sharp edges in the metal.
STEP 5 - Place louvers and rivet in hood: Lay the louvers over the holes you cut. Ensure that they are straight and covering all parts of the hole. Use a rivet gun to rivet the louvers in place.
STEP 6 - Trim hood insulator: Trim two rectangular holes in the hood insulator about the same size as the holes you cut in the hood with a razor blade. Make sure they line up with the louvers to properly divert engine heat out the new holes. Place the insulator back on underneath the hood using the provided clips and you're done. Since this install, I've noticed a drop in engine temperature, especially on long drives and very hot days.