4.0/4.6/P38A Air Box Replacement

Introduction
Andrew Parker, one if the pioneering 4.0/4,6 owners (see his other RR upgrades including his extremely professional air suspension lift) decided to upgrade his air intake filter to one of the aftermarket versions to enhance air flow (and therefore horsepower) while maintaining maximum filtering performance. After researching the available options, Andrew chose the AIRAID series of air filters, designed to boost engine horsepower by about 5%. (Their site has dyno figures for various filter and engine combinations).

Parts Needed
Some 3003 .050 thick aluminum sheet metal.
Some 7075 Alloy material as well.
One Air Aid 800-109 Air Filter.

Making a New Airbox
Remove the OEM air box and set it aside for cutting. It will be replaced by a new airbox consisting primarily of an aluminum panel closing off the forward left corner of the engine compartment. The new airbox draws air from under the headlamps (see below).

The airbox panel's form is figured using card stock. In order not to stretch the rubber coupler from the Mass Airflow Sensor (MAS) to the plenum, the panel has to be jogged back toward the plenum so the MAS ends up in the same location as before. The sheet metal is mounted under the EAS box's forward screws and onto the two studs that fix the head lamp into the body. The air temp sensor wires have to be lengthened by six inches or so.

Making the Components Fit
To provide a connection for the MAS tube to the new airbox, cut the old air filter box's tube from the lid as close to the wall of the box as you can with a hack saw. Cut a corresponding hole in the new panel with a jig saw and lots of WD-40 as the 3003 is gummy and soft. Use your work bench, some angle iron and some C-clamps for a break to bend it up. 3003 is very soft and easy to bend but only bend it once.

Fab a bracket for the EAS air dryer. I bridged from the power steering reservoir mount to the new panel using some 7075 and a bit of the aluminum angle (see photo below left).

The AirAid filter is a snug slip fit on the 3.375" OD of the air box lid's tube. The tube is fixed into the wall of the aluminum panel with a snug fitting hole and "Right Stuff" gasket maker. You can run a bead inside the panel and outside. The filter gets an offset from center hole drilled into the end for the temp sensor. I used a washer, some Loctite 242 and a nut to secure it in the filter wall's urethane end. Fabricate brackets to draw the filter onto the tube and keep it there. I threaded some M6 machine screws into two pieces of the angle aluminum and got some wing nuts to secure a 7075 alloy strip across the filter's end. This stuff is very stiff compared with the 3003aluminum alloy. So it holds its form and will keep the filter in place.

Modifying the Outside Air Intake
For maximizing horsepower, it is vital that fresh, cold outside air rather than the warm or hot air from the engine compartment be drawn in to the engine's air intake. The new filter box effectively screens off the hot air from inside the engine compartment, and to draw in plenty of cold outside air Andrew added slots under headlamp using a 2-1/8" hole saw and a hacksaw blade with vise grip. He lined the slots with steel wire galvanized mesh and spray paint inside the holes semi-flat black paint prior to installing with "monkey snot". Finished installation looks very professional!

Return to Upgrades
Return to RangeRovers.net

If you have corrections, comments or suggestions, email us.

Page revised February 1, 2012


The new airbox cut from aluminum, with the Air Aid filter in place. The design excludes hot engine compartment air from the intake, and also provides cool air for the EAS.	Position of airbox relative to EAS box. Note lengthened air temp sensor wires. Also note bracket to hold new air filter in place (see below).


Brackets for air dryer. Note bracket to hold the Air Aid filter in place, also visible in the two photos above. Also Note Andrew's EAS bypass system in forground.	Tube from old airbox glued to the new airbox panel with MAS tube conneccted.