Modifying the airbox

[777cupra]

Hi everyone,

Ive spent a fair bit of time reading up on modifying the standard airbox, most of which I have read from doing a search on here. I come accross a very interesting article which was :

http://autospeed.drive.com.au/cms/article.html?&A=0629

Basically if u read all 5 sections of it the guy talks about negaive pressures etc, i wont go into it as he makes a much better effort of explanin it than I ever could lol

I still have a few questions tho:

What does everyone consider better..ie performance, value for money, effort etc the modifyed airbox, or induction kit/ forced air induction?

Has anyone modifyed their airbox, and achieved "amazing" results?

Ive seen from pictures that most modified airboxs people have sanded off and smoothed off the insides, any particular reason why this was done, instead of creating a smooth surface with some kinda filler?

As for increasing the size of the air intake, is it possible to go too big in theory? I would of thought that possibly a massive intake would mean there is more air to move, but would it move slower? Im no makeing a very good explination of what i mean here sorry, I mean is the pressure gonna be less in a large air intake, thus makeing the air move slower?

does also the increased airflow give any "induction roar" effect?

sorry if any of this seems like "silly questions", really interested in your thoughts and experiences tho.

thanks

 

[RobM]

No air filter, box or combination of those is going to give 'amazing' results, as the VAG group did a pretty good job of it in the first place. You'll get 'good' results, subjectively, but never anything that can be called amazing.

Considering modifying your air box is free and the new ducting is around £20, I'd consider this to be a much better value for money option than an induction kit of CAI. The gains are proven and good, the cost is low, the negative affects are nill. Compared to an induction kit, which gives similar results, a nicer noise but potentially increased heat soak, I'd say it was a better option. But if you want a loud induction roar, an induction kit / CAI is the only option.

Re sanding the insides... this is done to give the smooth surface you need with minimum hassle. To use filler would create all sorts of potential problems, as you're adding an entirely new layer to the inside of the box which probably wont hold that well to the plastic and may come apart. Sanding simply gives a smooth finish without any risks, plus it's cheap and easy

 

[777cupra]

yeh the term "amazing" was kinda sarcastic, im not expecting spectacular, but any improvement is good, and yeah i agree about the heat soak, heard about problems with filter oil and MAF sensor, which I think has caused problems on a previous car of mine, so want to shy away from that.

as for the ducting, any ideas whether it is a case of bigger is def better, or should more importance be placed on smooth insides, and smooth angles when routing round things like the battery? if that makes sense? or would that not matter as much?

very good point on the filler, I hadn't thought of that! good job I haven't started doing any modifying yet to the box!

 

[RobM]

With turbo'd cars, bigger does equal better. With a N/A car the intake can be made too big, causing a drop in pressure, but when a turbo is added into the mix it's going to be sucking in what it likes anyway, so not so much of a big deal. I know that's an incredibly non-scientific way of explaining it, but I'm tired so Meh

 

[777cupra]

non scientific works well for me mate! I appreciate ur help...just got to hope for a nice dry weekend to get out n make me some big ol' intake! any other things you think i may need to consider that i may not of already thought about?

 

[J@mes]

do what i did (modified airbox(search! )) and get that new split r or what ever its called forge DV!

same performance as the best CAI at a fraction of the cost

 

[Bogwoppit]

That article on modifying the airbox and removing pressure losses was an interesting read, I was suprised to see the gain from descreening the MAF.
Quite amusing that after all those flow gains achieved, then ECU couldn't compensate.

 

[RobM]

I laughed at that too! All that hard work to improve air flow, and the ECU decides it doesn't like that, so drops boost

 

[danieltm]

i got a NEW air box from ebay for just £21 inc p&p This is for me to smooth out as i dont want to mess up the one i have already got. Anyway as i was smoothing the top section of the box i some how managed to put a tiny hole in one corner, i filled the hole with chemical metal. I was just a bit worried it will not hold to the plastic? What do you all think? If it was to drop out could it be a problem?

 

[J@mes]

i personally would have used a bit of black silicon sealant!

 

[danielbarnett]

depends where it is? Anyway an airbox with no holes in can still suck in dust, grit, leaves etc - anyone checked their airbox lately!

 

[J@mes]

if the hole is in the bottom of the airbox it prob doesn't really matter too much (mine has a hole there as standard!) and as for dust/grit/leaves being sucked up... don't worry about it... this is why we have a filter element!


(but do clean it once every so often)

 

[777cupra]

I laughed at that too! All that hard work to improve air flow, and the ECU decides it doesn't like that, so drops boost

any ideas on how to improve flow and avoid ECU throwing its toys out the pram n dropping boost?

 

[Mitchy]

do what i did (modified airbox(search! )) and get that new split r or what ever its called forge DV!

same performance as the best CAI at a fraction of the cost

Strange that as it contradicts my findings

I have a BMC induction kit on my LCR, and thought i'd test out this airbox theory a couple of months back. I'd read good reviews from yourself and a couple of other people.

So i went and bought a dremmel tool £40ish and a green panel air filter £40.

I smoothed the airbox, which took at least 3-4 hrs to do

Before i took my BMC airbox off i did some airflow vagcom readings beforehand to get it as ''scientific'' as possible for comparison purposes. I then took the BMC out and replaced it with the modified airbox and panel filter, it was immediately 5-6g/s of airflow down in value. (This was 1/2 hour after removal of BMC)

I did quite a few tests and each time around 5-6g/s down. I then reset the ecu and did a throttle body allignment and again went out and done relogging to find exactly the same results. I left it on my car for about a week and measured airflow again at the end of the week.

I did logging again of the airbox, just before re-fitting of my BMC for direct comparisons and 1/2 an hour later after BMC was fitted back, airflow again was showing 5-6g/s of additional airflow.

So from my findings i was dissapointed and its not as good as the CAI BMC. It may be better than a standard airbox, but from my own evidence, it is not as good as the BMC.

Its not as cheap as you think either, especially if you dont have a dremmel tool as that will cost you around £40. Along with the cost of the panel filter £40 and cold air feed (£10) and obviously the 3-4hrs time it takes to do aswell.

Your just as well spending the £175 and getting the BMC if your after max airflow. If your after an increase in airflow over standard and want to do it on a budget then modifying the airbox is probably best bet

But for maximum airflow, from my own evidence a CAI kit is definitely better

 

[UncleFester]

Could any one work out just how much difference 5 to 6 g/s is going to make?

 

[RobM]

Could any one work out just how much difference 5 to 6 g/s is going to make?

I'd bet it's not £175 worth of difference

 

[J@mes]

Strange that as it contradicts my findings

I have a BMC induction kit on my LCR, and thought i'd test out this airbox theory a couple of months back. I'd read good reviews from yourself and a couple of other people.

So i went and bought a dremmel tool £40ish and a green panel air filter £40.

I smoothed the airbox, which took at least 3-4 hrs to do

Before i took my BMC airbox off i did some airflow vagcom readings beforehand to get it as ''scientific'' as possible for comparison purposes. I then took the BMC out and replaced it with the modified airbox and panel filter, it was immediately 5-6g/s of airflow down in value. (This was 1/2 hour after removal of BMC)

I did quite a few tests and each time around 5-6g/s down. I then reset the ecu and did a throttle body allignment and again went out and done relogging to find exactly the same results. I left it on my car for about a week and measured airflow again at the end of the week.

I did logging again of the airbox, just before re-fitting of my BMC for direct comparisons and 1/2 an hour later after BMC was fitted back, airflow again was showing 5-6g/s of additional airflow.

So from my findings i was dissapointed and its not as good as the CAI BMC. It may be better than a standard airbox, but from my own evidence, it is not as good as the BMC.

Its not as cheap as you think either, especially if you dont have a dremmel tool as that will cost you around £40. Along with the cost of the panel filter £40 and cold air feed (£10) and obviously the 3-4hrs time it takes to do aswell.

Your just as well spending the £175 and getting the BMC if your after max airflow. If your after an increase in airflow over standard and want to do it on a budget then modifying the airbox is probably best bet

But for maximum airflow, from my own evidence a CAI kit is definitely better

I hear what your saying Mitch and believe you but two questions?!

what size cold air feed did you use? the normal 80mm size or the fat 104mm size that i use?!

plus did you use Feel's battery relocation brackets like me too?!


I did before and after logs of my modded air box to the OEM set up and got a good increase in flow (4% from memory!) so for £80 all in that wasn't bad at all (filter, feed and battery relocation brackets)

I see 210g/s at most but normally low 200s i think when the weather is HOT!

as we both know ko4 cant flow more than 210 g/s (realistically!) so for the money modded air box is the way to go for me! if money is no limit you may aswell get the £200 (or watever it is) BCM CDA (originally that was my first choice!) as it looks cool and sounds slightly better/throatier than a modded airbox.

thats my 2p worth!

 

[Bogwoppit]

any ideas on how to improve flow and avoid ECU throwing its toys out the pram n dropping boost?

I don't think you will create enough increases to worry about this. The guy on the article ended up creating a ramair system to actually cause his ECU to throw a wobbly.
By some means if you do create an excellent ramair system, you will have to get the car remapped to compensate.

 

[RobM]

A remap is probably the only realistic way to ensure the ECU doesn't ignore the increases actually.

 

[J@mes]

as far as i know our ECUs can compensate for quite a lot, 20% adaption i think it is!

so no matter what air filter you use you should be fine!