The stock air box is restrictive and the stock air filter doesn’t offer the best filtration. An option is to remove the stock air box setup entirely and replace it with a higher flowing better filtering Donaldson 6637 air filter. A simple filter, adapter, and clamp allow the filter setup to replace the stock air box.
The easiest way to get everything you need is to buy a kit from Riff Raff Diesel that comes with your choice of air filter, clamp, adapter tube, and a Riff Raff pre-filter cover as well.
You may be able to save money by sourcing the parts together and doing it yourself DIY but it is hard to beat the simplicity of a kit. You need the air filter, about a 3 to 4 inch section of 4″ O.D. tubing for 99.5 to 2003 model 7.3psd or a 45* bent section of tubing for 94 to 99 7.3psd, (exhaust tube is the thinnest inside allowing for more air flow but pvc could work as well), and a 4″ clamp preferably a T bolt clamp but a ring worm style clamp will work it just will not be as strong to hold the filter onto the tube. We recommend using a true Donaldson air filter however there are other similar filter options including the more affordable NAPA 6637 filter, WIX 6637 Fleet Filter, or even the AFE BIg Boost air filter.
With either option you choose you must remove the stock air box. This means un-clamping the intake hose from the lid, removing the lid, then air filter, and unbolting the 2 bolts from the bottom of the air box to release it, lastly the air filter flow gauge if being reused and the air temp sensor needs to be removed from the air box. If you have a kit to keep using the air filter flow gauge it needs to be removed and installed into the adapter pipe. If doing this yourself or if you do not then filter gauge can be placed somewhere it fits like under the new air filter and or zip tied so it doesn’t move. The air temp sensor can also be set below the new air filter and or zip tied to something so it still functions but can’t bounce around.
An optional step which makes more room is to remove the air box portion of the battery tray. This is a permanent change as it requires cutting off the air box portion away from the battery tray. To remove the battery air box tray you must remove the driver side battery so you can access the 4 bolts to free the tray. Once the tray is removed you cut off the air box portion of the tray then reinstall. You do not have to remove the tray however doing so makes more room for the air filter and it allows for the use of a 6637 mounding bracket sold by Riff Raff to keep the air filter up off of the fender while still fitting under the hood. It is possible for the hood to dent the round shape of the air filter otherwise. Now that the air box is out to install the filter you attach it to your 4 inch section of 4″ O.D. pipe and then the filter attached / clamped to one side of the adapter or 4″ tube and the other end gets inserted and clamped to the stock air hose. This allows the CCV to remain in tact and simplifies things by just replacing the air box. Lay the air filter where it fits best and cant get damaged by the hood (less a minor dent) and you are done.
A great write up of instructions with some pictures can be found at ford-trucks.com
Although this is not a cold air intake this stock air box replacement with a high quality 6637 air filter allows for less restricted air flow. Note that this air filter will be noticeably louder than an air box. You will hear more turbo sound to escape while driving.
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