P38 Air Box Upgrade for LPG 

overall af install 1 copy.jpg - 49112 BytesIntroduction: Why Replace the Air Box?
Parts Required
Putting it all Together
Other Possibilities


Introduction: Why Replace the Air Box?
For those owners who run their P38A on petrol or diesel only, this modification may have little interest. After all, the factory airbox does the job quite well. However, if your car is modified to run on LPG (Liquified Petroleum Gas) you may have experienced the occasional engine backfire. Ron Beckett of Australia had a number which were severe enough to blow the airbox apart. After replacing it, he had several other backfires which again destroyed the air box. Despite repairing the box, it soon became apparent after even more backfires that there had to be a better option than spending more than A$200 for a replacement air box. Further, the explosive forces were severe enough to lose the clips which held the lid onto the box - and they can't be purchased separately, thus rendering the airbox useless even if it could have been repaired. The idea for the conversion came from Andy Cunningham in the UK.




Parts Required
Ron wanted to minimise the use of non-Land Rover parts in this conversion and, after seeing how Andy Cunningham had used a cylindrical air filter from a Rover SD1 car, Ron visited his local independent LR mechanics and had a delve into their second-hand parts bin and came up with a couple of different cylindrical air filters from different model Range Rovers. After playing around with them he selected the filter shown (obtained from a Series I Discovery) for the main reason that it fitted and clipped onto the P38A MAF sensor duct perfectly thus obviating the need to make up an adaptor. All he had to do was work out how to mount the filter and, equally important, how to support the EAS dryer which previously had been bolted to the original air box. The part number of the air filter housing is NTC......

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The air filter case is normally supported at the inlet end by a bracket with two pins which fit into rubber grommets in the lower mount (see above). The rear mount (at the outlet end) also fits onto pins in a mounting bracket. The filter is not bolted in. Ron happened to have the front bracket left over from a modification to the air filter on his '86 Range Rover so that solved one problem. It only needed to be bent slightly to allow for the angle of the downward filter.

The rear mount turned out to extremely simple, too. A piece of 2" (50mm) square tubing with a piece of 3/8" (10mm) rod welded into the centre of one side of the tubing. A hole was drilled through the bottom surface to align with the already existing threaded hole for the original air box mounting.

One last job is to remove the air temperature sensor from the original airbox lid and fir it into the neck of the replacement filter. This is simple as the sensor screws into a backing plate which Ron removed from the airbox.

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The space vacated by the original airbox. Note the rear threaded mounting hole will be used by the new installation.

Closeup of the rear support. Not seen in this photo is the hole in the lower surface through which it is bolted to the threaded hole mentioned in the previous picture. The hole is offset from the centre.

Dryer Mounting

As previously noted the EAS dryer is normally bolted to the side of the airbox so a new method of mounting it is required. Ron fabricated a simple bracket that is bolted to the front edge of the inner fender thus keeping the dryer approximately in its original location. The avoided the need for new air lines. If one wanted to make new air lines up, it could be relocated elsewhere.The mounting bolts are accessible from underneath without removing the plastic wheel arch liners under the fender.

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The bracket to support the dryer - made from 2mm steel plate. Ron plans to replace this with another that will have a bigger foot to better withstand the vibration of corrugated dirt roads.

Note how the foot of the bracket is a bit on the small side. The two bolts holding the dryer to the bracket are those which held the original airbox in place.

Putting it all Together

The air filter housing merely pushes forward onto the two backward facing pins of the forward mount. Then the rear is pused down onto the rear pin. The MAF sensor duct is then mated to the rear of the filter housing and the clips locked.

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The clips and swaged end of the filter fit the MAF sensor duct perfectly.

The air temperature sensor from the destroyed airbox was refitted into the neck of the replacement filter.

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The final installation from above. Ron will probably seal the original air intake to the right of the air cleaner.

Other Possibilities

Another possibility is to fit a K&N pod filter. Ron cut off and saved the outlet off the destroyed airbox lid to see if it would fit a K&N in the future.

If you want more power, another option is the Air Aid series of filters, designed to increase air flow -- see the page on upgrading to an Air Aid filter to increase power output

Or if, like Chris Crompton, you removed the EAS and made up a snorkel, it might feasible to reconfigure this air filter so that it mounts where the EAS valve block is mounted and face it toward the side of the car. In that way the duct from the snorkel could be fitted directly onto the inlet side of the filter. This would reduce the length of the snorkel duct and the restrictions to the airflow.





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Page revised February 1, 2012