Passat B5 Air Box Drill Mod

Drilling your airbox is the easiest and cheapest modification you can make.  I did mine while changing the air filter, its a good alternative to replacing the air filter with an induction kit which will be exposed to the engine heat and often not do any better than the OEM air filter.

Tools required:

• Drill
• 25mm drill head piece
• Socket wrench
• 8mm socket head

Firstly remove the air flow plastic pipe that sits over the airbox by the passenger headlight.  It will simply pull off from one end.  Unclip the airbox housing cover, there are four clips, one by each corner.  Lift the cover up and out of the way.  You do not need to fully remove the top cover as it may still have the OEM locking clips holding the pipework together which will need to be replaced by jubilee clips if you do take them off.  Remove any wiring or pipework that may sit in the way by lifting up and pushing to one side.  You wont need to actually take off any parts but may need to negotiate them to avoid obstruction.

Lift out the old air filter which if it looks anything like mine did then can go straight to the bin.  Next you will see a bolt to the inner wing from the airbox housing.  Remove the bolt and lift out the bottom of the airbox which sits on two rubber bungs.

Clean up the bottom of the airbox and remove any debris and loose dirt.  Its not adviseable to wash the box unless you have the time to leave it out to fully dry, but to be honest a good brushing and wipe with a clean cloth will achieve the same results.  Now look at the sides of the airbox and select suitable positions for your extra holes.  Try not to position your holes over the criss cross of the plastic as its the structure to hold it in its shape.  I found several suitable positions which lined up with each other.  These holes will not be visible once you have refitted the box but its a good idea to drill where it will gain the most natural air, near the front is best so the holes sit behind the passenger headlight.  I used a standard 25mm drill tip which can be purchased from any hardware store.  You can drill individual smaller holes if you only have small drill tips, and in this case it would be best to bunch the holes together and form a grid.

Once you are satisfied with your drilled holes use a stanley knife or curved file to remove any plastic bits still attached to the edges of the holes you have made.  Refit the airbox housing and refit the 8mm bolt.  Carefully fit the airfilter and refit the top of the airbox and clip down the four holding clips.  Done.

Now take your car for a drive around the block.  Depending on how many holes you made and how much surrounding noise you have you should hear a slight sucking sound from the air being drawn into the filter.  This modification will not affect the fuel economy or give any negative effect to the engine, but also it wont give you turbo speeds and massive power hikes.  Its a small mod that may free the air flow into the engine slightly and give a slightly smoother acceleration but for the time it takes and the cost its well worth doing especially if changing the airfilter anyway.

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