i managed to buy a second-hand airbox off Oliver so i can begin trying out this "swiss cheese" airbox mod that's quite prevalent in vwvortex. basically, you take the bottom half of the airbox out and make holes around it to allow more air in, effectively increasing the air-flow into the intake which should translate to some sort of improvement. i followed vwvortex member Breezy's set of DIY instructions when doing this as in my eyes, i thought this was the most effective/logical - instead of making many holes, he cuts out a whole section of the airbox out, pretty much opening it up. seeing as i haven't written a DIY for a while, i'll write my take on it (since the 2.0L 8V airbox is slightly different to the VR6 that is owned by Breezy.
- plier (adjustable plier may be required)
- selley's supa glue (or equivalent)
- 60/200/400 grit sandpaper
- mallet (not required but may help)
- permanent marker + ruler
- power drill
- cutting tool (whatever you fancy; Breezy used a dremel, some other forum members used a sharp knife with a lighter handy, others drilled holes until a whole section can be cut out; i used a jigsaw cos i didn't have anything else in handy :P)
- MAF sensor cleaner (e.g. CNC-brand; see below)
- high-flow aftermarket panel filter (e.g. K&N; see below)
(optional; you may want to wait it out until your current air filter is to be disposed if you want to get the most out of it, or you can just stick with standard air filters - up to you)
- CNC MAF sensor cleaner (helps remove any impurities that may block the sensor, causing faults)
- K&N filter (#33-2069 for most Mk3 Golf/vento/jetta)
- as a cautionary step, unhook the negative terminal of the battery. we will be unhooking sensor plugs and will be removing the airbox + filter temporarily, so we don't want anyone accidently starting the car up.
- remove the air filter the way you normally do when servicing it: unclamp the hooks that hold the top half of the airbox. unclamp the intake hose that connects to the MAF unit of the airbox by using the pliers. release the connector attached to the top half of the airbox. remove top half of the airbox and carefully take the air filter out --> give it a thorough shake/superficial clean and leave it in a relatively clean/dustless area.
- unhook the two rubber elastic belt-looking things that hold the bottom half of the airbox in place (if it helps, they are facing the alternator). take out the airbox.
- remove top half of the airbox from the MAF unit by unscrewing the top screws (x 4).
- give the whole now-exposed engine bay area a thorough cleaning, using degreaser for hard to clean spots if required. cloth-dry or air-dry.
- let's look at the top airbox now - take out the large tubing that has the rubber seal on top (i.e. that faces the MAF unit). before:
recover the rubber seal, and using supa glue, stick it in the same location to where it normally would be when the tubing is present to push it against the airbox. this is important as without it, there will be a sizable gap that will allow unfiltered air (even water) into the engine. after:
- moving on to the bottom half of the airbox - this is the hard part. attempt to take out the velocity stack inside and the J-tube outside of it. these two parts are actually one piece (two longitudinal halves) so the only way to take them out is to break them.
it was extremely difficult to take them out without risking damage as the outside parts were both larger than the hole that separates the two. after half an hour or so, i ended up breaking the tabs inside of both tubes using a flathead so i could stretch and break them out. they're no longer needed anyway, but if you can remove it without breaking it, thumbs up to you. the mallet may come in handy to break those things to get easier access.
- now the fun part; the chopping! first off, using Breezy's modded box and mine in the pictures below, work out whereabouts to cut the airbox first. REMEMBER that you need to cut the airbox on the front fender side, i.e. the section furthest away from the engine.
mark out neatly approximately the lines you will cut to make the section. using the power drill, drill multiple holes on the corners. keep in mind that i used the jigsaw, so i needed a starting point in order to wedge the cutting piece into place.
with whatever cutting tool you use, be CAREFUL and proceed on slowly and with much caution. work your way around until the section is off.
- using sandpaper, smooth out the cut edges. it's quite important so as to ensure the air flow is as smooth as possible (this has already been disturbed after you cut the airbox, but you might as well make best with what you have).
- with that done, you've basically finished the bulk of the airbox mod. clean both halves of the airbox and the exposed engine bay area after taking the airbox out. cloth-dry or air-dry.
- while you wait, look for some plastic pieces towards the corner of the fender and headlight area. pull them out and you will reveal a pretty big hole. hopefully, this will be your source of "cold air".
the above picture shows the two (useless) plastic pieces on the right, with the exposed hole in the middle left.
in Breezy's DIY, he removes a mesh component of the MAF unit. looking at my MAF unit, it appears to be noticeably different to what he had:
i took this pic when it was still attached to the airbox, but the mesh appears on the other side. it doesn't look like to be made of ABS plastic, like Breezy's, but looks more like the "fly-screen" type. removing it was not possible by just using minimal force, so i just kept it there. it didn't look as restrictive as what Breezy had though.
- clean your MAF sensor using the specialised MAF sensor cleaner. make sure to follow the instructions.
- once airbox and engine bay area has dried, place the bottom half of the airbox back into the same location. reattach using the rubber elastic belt thingies.
those are the "after" pictures. check to see how the opened up fender hole meets the cut section of the airbox dead on, and that it is not facing the engine.
replace the air filter back on - either use your current one or have a new one (preferably high-flow one).
reattach the MAF unit to the top airbox using the four screws, and check for gaps. carefully replace the top half of the airbox onto the bottom half of the airbox, and make sure a secure fit is secured. reclamp the intake hose (may need adjustable pliers for this one) and the two airbox clips, and reattach the connector back onto the airbox.
- rehook the negative terminal of the battery, and start playing :)
now for the obligatory claim - what you do with this guide is up to you. it is merely a guide and in no way am i claiming that this mod is 100% safe for your car. the steps you go through are solely your own responsibility. proceed with this mod in caution. but hey, it's not that bad of a mod :D
happy heavy foot-ing.