!!! Vw oem cold air intake !!!

Welcome to the
!!! OEM COLD AIR INTAKE !!!
Below is the best possible routing and design for a cold air intake on a VW MK4 unless modified to some ungodly HP!
Reality is that having a vacuum within the air box for air to expand into cools it down. This is accomplished by utilizing a sealed box that you control the dynamics and operation. Aftermarket CAI's generally have poor design and very few have a sealed plenum making them Warm and Hot air intakes, not Cold Air Intakes.
Below is the tube that wraps around the battery, it's sized larger than the lower boost pancake tube. (which is a far better place to consider an upgrade to the OEM system with an OEM designed part using the upgrade metal lower boost pancake tube.)
The tube below is designed with specific flow rates being considered and on a stock to fairly heavily modified engine it is more than adequate. It's actually designed to create a low pressure, to vacuum within the plenum to cool the incoming air.
The added tube on the upgraded 1.8T plenum box (in one of the last pictures below) that points towards the engine is the OEM upgrade for vehicles with greater modifications that might occasionally need to draw a bit more air than the tube around the battery can provide. This is the only modification to the stock air box that is affordable and will actually make any improvement, luckily it can be found in the junkyard on an old car for a much better price than an aftermarket CAI.

Cold air duct around battery:





Where it comes out in front of the battery and behind the headlight


This is the area beside the battery and to the right is the opening for air to enter.


The same picture as above with the rear cover below installed creating the completed cold air intake. Notice there is no opening between the battery as the rear cover is specifically designed for this vehicle.


The inside of the rear cover


This is the bottom of the 1.8T air box to the left you have the added volume air valve tube that points towards the engine above trans.


This is the CAI installed


The picture below show's the bottom of the original ALH CAI filter plenum which only has one inlet for air.

Do some reading.



The stock airbox is MORE than you will ever need, no matter how much you modify your car. And K&N oil type air filters are BAD for your MAF (certainly if left with too much oil, and maybe period).

scooperhsd said:

Do some reading.



The stock airbox is MORE than you will ever need, no matter how much you modify your car.
And K&N oil type air filters are BAD for your MAF (certainly if left with too much oil, and maybe period).

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Yea I’m pretty sure someone tested the stock airbox and determined it was adequate to
beyond where you would be maxing out the MAF sensor anyway.
Been a while since I read up on it... 200+hp comes to mind but i could be wrong.

ketchupshirt88 said:

Been a while since I read up on it... 200+hp comes to mind but i could be wrong.

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The 1.9T base I posted above was VW's solution, as stated in the original post, to higher needs for incoming air.
It will draw warm air through the added draw tube, however, if there's that much need for air a little warm air isn't going to hurt.

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BEWs have them too. But I doubt any of the diesels really are capable of moving so much air that the normal intake tract isn't sufficient. The turbocharger's inlet is the restricting factor, and it is barely bigger than a silver dollar.... seriously, it is less than 1.5" across. It is TINY. Even a bigger turbo mounted to an ALH is STILL relatively tiny and this is only a 1.9L engine that in stock or even mildly modded form makes very little usable power over about 4k RPM anyway.

I have seen a 212hp dyno plot from an ALH with the completely stock air intake intact, right down to the snowscreen and the OEM Mann air filter. If you want to go faster, the air inlet system is NOT the first place to start. It is probably #12.

oilhammer said:

BEWs have them too. But I doubt any of the diesels really are capable of moving so much air that the normal intake tract isn't sufficient. The turbocharger's inlet is the restricting factor, and it is barely bigger than a silver dollar.... seriously, it is less than 1.5" across. It is TINY. Even a bigger turbo mounted to an ALH is STILL relatively tiny and this is only a 1.9L engine that in stock or even mildly modded form makes very little usable power over about 4k RPM anyway.
I have seen a 212hp dyno plot from an ALH with the completely stock air intake intact, right down to the snowscreen and the OEM Mann air filter. If you want to go faster, the air inlet system is NOT the first place to start. It is probably #12.

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Seems like you're trying to tell me something that this post is absolutely all about. There's no better intake for the MK4!
You're right though, a TDI would likely never open the other tube to draw air. One more reason there is no CAI that would viably replace the OEM CAI.
Guess where I got the 1.8T airbox, the recipient 1.8T for the swap. Figured WTH, it's sitting there, may as well...
http://forums.tdiclub.com/showthread.php?t=491470

I hate big pictures and scrolling to read the post...

My Cummins, which is a stock 190 hp has a smaller air cleaner than my MK4. That must tell you something. I've never felt the need to
increase my Cummins air cleaner... (note: no scrolling necessary)

I thought they had a section for "Unnecessary Upgrades". If not, I suggest they make a special category for such things.

While your at it, you could install a 4" exhaust to eliminate back pressure.

eddieleephd said:

Seems like you're trying to tell me something that this post is absolutely all about. There's no better intake for the MK4!
You're right though, a TDI would likely never open the other tube to draw air. One more reason there is no CAI that would viably replace the OEM CAI.
Guess where I got the 1.8T airbox, the recipient 1.8T for the swap. Figured WTH, it's sitting there, may as well...
http://forums.tdiclub.com/showthread.php?t=491470

Click to expand...

There is that thread that I came across with the occasional TDI having issues with the N75 valve due to a vacuum in the air box not allowing the vent release the actuator fast enough causing over-boost. I found it because I was researching my N75 valve issue yesterday.

Franko6 said:

I hate big pictures and scrolling to read the post...

My Cummins, which is a stock 190 hp has a smaller air cleaner than my MK4. That must tell you something. I've never felt the need to
increase my Cummins air cleaner... (note: no scrolling necessary)

I thought they had a section for "Unnecessary Upgrades". If not, I suggest they make a special category for such things.

While your at it, you could install a 4" exhaust to eliminate back pressure.

Click to expand...

me too, sorry, will change somehow.


Alright thumbnailed, because I wanted to figure it out.

I read about a guy who cracked his windshield because of too much torque with a BEW engine.

I think he had the stock airbox.

Yep. So long as the factory snorkel and those plastic covers behind the left headlight are still installed, you have a far more effective cold air intake than any aftermarket solution.

It's as if ze German engineers know what they're doing better than some small fry company hacking **** together in a little shed. Weird.

What old boy told you that tale?

Mike_04GolfTDI said:

I read about a guy who cracked his windshield because of too much torque with a BEW engine.

I think he had the stock airbox.

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Sounds like he said it was the torque, but, it was the rock from the car ahead of him that cracked the windshield most likely.
There's not enough torque that could be put out with the traction barrier of the tires breaking loose to cause the shock needed (shock is the only thing that breaks glass) to break, or enough flex to crack, the windshield.
Good story though, huh...

Franko6 said:

I hate big pictures and scrolling to read the post...

My Cummins, which is a stock 190 hp has a smaller air cleaner than my MK4. That must tell you something. I've never felt the need to
increase my Cummins air cleaner... (note: no scrolling necessary)

I thought they had a section for "Unnecessary Upgrades". If not, I suggest they make a special category for such things.

While your at it, you could install a 4" exhaust to eliminate back pressure.

Click to expand...

Ditto..........

Proportionately, the air filter on the 5.9 Cummins in my RV and my Dodge Shop Truck are both smaller than the OE air filter in my Jetta TDI. And, they (RV & Dodge) are both "Factory Cold Air" set-ups by design as well as the one in my Jetta.

In my Vanagon ALH set-up, I'm using the same size filter as fits my Yanmar Excavator with a 3-cylinder .... designed to work in dust, which has a surface area slightly more than the Jetta OE filter.

No comment on Exhaust (it comes out a very tiny hole at the Turbo,,, oops, I didn't mean to say that!)..

AndyBees said:

Ditto..........

Proportionately, the air filter on the 5.9 Cummins in my RV and my Dodge Shop Truck are both smaller than the OE air filter in my Jetta TDI. And, they (RV & Dodge) are both "Factory Cold Air" set-ups by design as well as the one in my Jetta.

In my Vanagon ALH set-up, I'm using the same size filter as fits my Yanmar Excavator with a 3-cylinder .... designed to work in dust, which has a surface area slightly more than the Jetta OE filter.

No comment on Exhaust (it comes out a very tiny hole at the Turbo,,, oops, I didn't mean to say that!)..

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It's all about surface area of the filter, not so much the size of the plenum it's in. A lot of small filter housings have filters pleated 2 and 3 inches vs our stock inch and a quarter to half with prefilter.
The difference between gas dynamics under pressure versus under ambiant, or under vacuum are very different and velocity plays its part, as does temperature.
The possibility of overboost on an engine tuned in excess of 200hp is greater with the stock air box, however, a simple filter on the N75 vent line would fix that and retain the improved cooling of the incoming air at the greater velocities required to create enough vacuum to cause such an issue with the N75 not venting fast enough to cause overboost.
Which amusingly enough has nothing to do with the plenum being large enough to supply the air needed to overboost at such HP. It will supply enough air for 250 to 300 HP, however, doing so could cause enough vacuum under that amount of boost that it doesn't release the vacuum actuated boost control fast enough causing overboost, or turbo runaway (wonder how many HP that would take, a F-ton) which is difficult without added fuel propelling it, unless it vaporized and sucked up the oil in the intake and engine runaway accomapnied it.
Which is an extreme stretch of the imagination, maybe.



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eddieleephd said:

Sounds like he said it was the torque, but, it was the rock from the car ahead of him that cracked the windshield most likely.
There's not enough torque that could be put out with the traction barrier of the tires breaking loose to cause the shock needed (shock is the only thing that breaks glass) to break, or enough flex to crack, the windshield.
Good story though, huh...

Click to expand...

It was member n1das.

Thread: http://forums.tdiclub.com/showthread.php?t=471195

Post: http://forums.tdiclub.com/showpost.php?p=5200602&postcount=2

"I managed to crack the windshield due to twisting the body from enjoying the weapons-grade torque."

For those considering air intake mods:
From doing some reading and research for my wagon build, I found some math that was WAY over my head. A lot of smart people on this forum can figure it out and maybe explain it, but I can't. From what I understood, that factory plastic pipe that goes behind the headlight is rather sufficient for almost everyone with an ALH(I was doing research that's 99% based on this engine, since that's what I have). The factory airbox is plenty with a factory VNT15 and even with a slightly larger 17. The oem filter flows well enough and doesn't sacrifice filtration for airflow, doesn't send harmful particles into the compressor and basically is a cheap part that just works. The PD150 airbox and snorkel or the .:R32(w/DSG option) IS an upgrade. It's internal design can net some extra, but it's largely for heavily modified engines. The intake ducting past the airbox is ok and the OMI is helpful by making the airflow more laminar, but it doesn't net power just by itself. A lot of it depends on the power goal and the turbo you're using to reach that goal. That will dictate how much air you're going to be moving. Air speed is a factor here as well. You can absolutely grab larger piping and replace the snorkel and all the piping up to the compressor with a larger 3" pipe, but it would drastically change your air speed through those pipes and it may actually hinder performance within the majority of the powerband. It could potentially give you a slight nudge at the very tippy-top, but you're going to lose more at the bottom. You're not going to be at or near the redline most of the time, so it's a mod, but not a helpful mod. It's more of a combination of parts. You have to put together a package of parts that work together and nets a result. Each part by itself can add very little, if any.
I'm not saying don't do it. It's your car, your money and your effort. Just know what it's going to do and how it does it, before you do it.