"Cold-air intakes" and "high-flow air filter" FAQ

[TDIMeister]

By popular demand, here's an FAQ thread for USEFUL information on cold-air intakes and high-flow air filters. Useless posts will be removed.

Go nuts.

Edit: know what would be cool? Maybe someone can make a nifty, tastefully funny but small and useful button picture that links to this thread for future threads discussing this subject. This would be a useful thing to do for other FAQs as well. For your convenience and a start, you can copy and paste this hyperlinked thing to offending threads:

Read the "Cold-air intakes" and "high-flow air filter" FAQ!

 

[scurvy]

Reposted from here by request of TDIMeister.

In response to the statement, 'because they [K&N filters] are a proven way to make power on nearly every other car.'

No they aren't.

http://www.honda-tech.com/showthread.php?t=1768602
No gain in HP or torque (tiny bit more torque with stock system)

http://forum.e46fanatics.com/archive.../t-378208.html
'The Porsche Club of America dyno-tested K&N filters in a variety of new Porsches in 2001 and found no power increase whatsoever.'

http://www.apriliaforum.com/forums/s...postcount=3562
'On my old 1999 Mille I did a dyno test with full EGA on the stock filter, EVO, K&N, a Foam one I made and none at all. The dyno graphs all directly overlaid one another as did the mixture trace lines.'

http://www.gadgetonline.com/Dyno.htm
' It looks like TRD is right about this one, or close anyway. They told me that they have seen a slight reduction in power, to no improvement with the installation of the K&N FIPK.'

http://tl.acurazine.com/forums/showthread.php?t=601091
'The reality is 4.6 RWHP and ZERO gain in torque is PEAK number. The 4.6 additional horsepower did not increase the entire length of the curve...only a small peak at the high rpm.
...
Notice the red and blue line pulls are identical to each other with the difference of 4.6 RWHP [at one point, approximately 5400 RPM]. This peak number would not be felt on the street or shown in the 1/4 mile.
...
Then you have to consider how the K&N works in the first place. It allows more air to travel through it so no matter how many ways you look at it, the K&N filters less particles. It has been proven that an engine equipped with a K&N filter will show more silicate in it's oil than an engine with a "paper" element. Don't believe me? Analyze you own oil before and after a K&N install. I did.'

http://webspace.webring.com/people/m...nisign/kn.html
' I know of at least one Si/SiR owner who dynoed their car before and after installing a K&N drop-in like yours and mine, and saw horsepower losses.'

I could go on, but the claim of these oiled MAF-ruining bugcatchers making power 'on nearly every other car' doesn't hold water. Even if you don't believe the HP gains, the lack of filtration is my biggest concern. Price out a replacement MAF & turbo for S&G, or a valve job.

 

[n1das]

K&N filter media, notice the sunlight passing thru the filter!

dieseldorf's K&N "lie detector" test:

From what I can tell from the dyno plots:
- 1st run: Baseline with NO FILTER installed. EMPTY airbox!
- 2nd run: Stock OEM paper air filter.
- 3rd run: K&N air filter.

ZERO performance improvement observed with K&N compared stock OEM paper filter or even NO FILTER at all! We've seen this all the time in the numberous K&N threads..."It (K&N) just HAS to be better!" OK, based on what?

As I've said in other K&N filter threads:

K&N filter = MAF eater + engine sander + ZERO performance benefits = BAD!

Stick to using only OEM filters:

I use the cold climate version OEM filter, shown in the above pic. Here is an end-shot view:

I use the cold climate version year round in my 02 Golf because I removed the snowscreen in the intake snorkel due to it regularly getting clogged with bugs and other debris.

Cold Climate version part number: 1J0 129 620 A
Standard version filter part number: 1J0 129 620

Note the "A" on the end of the part number is for the cold climate version.

 

[dieseldorf]

These products are consumed by those praying for miracles. Just say no, and save your pennies for something with a tangible payback!

 

[Drivbiwire]

 

[Drivbiwire]

That's the dirt let thru after just 501 miles of driving on a NEW FACTORY OILED K&N

 

[Drivbiwire]

Best bang for the buck

Plus

Or if you have a Mercedes it's already built into the MAF sensor (a "Delta-P" or Differential pressure sensor monitored by the ECU)

Speed: 80 mph
Total miles on air filter: 34,000
Ambient temperature: 74F/23C
Altitude Sea Level
Atmospheric pressure: 1004 hpa (Below standard of 1013)
Boost pressure (psi) 6.382 steady
Induction temperature post turbo (after intercooler) 39C/103F
Pressure drop accross the air filter with the above condtions: 3hpa or 1" WC!

----------------------------------------------------------------------------------

Full Throttle run different day, high elevation:
RPM: 2707
Intake Air pressure: 861 hPa
Boost Pressure: 2192 hPa/31.79psi
Charge Pressure Positioner: 52.6%
Boost Air Temperature: 41.4C
Outside Air Temp: 27.7C
Atmospheric Pressure (absolute): 903 hPa
Barometric Pressure: 1019 hPa
Pressure Altitude: 3151.7 Feet Above Sea Level
Density Altitude: 5383 Feet above Seal Level

Total Pressure drop at full boost = 42 hPa/16.8" WC/.609psi/1.24"hg

General rule of thumb:

Replace the filter when:
-25-30" of H2o restriction
-4 years
-100,000 miles
-Whichever occurs first.

If you have a Snow Screen installed, clean it every 10K by removing ONLY the base retaining bolts, NEVER EVER open a filter to take
a Look, if you want to inspect the filter, it can be viewed on both sides when removing the UNOPENED BOX from the car.

-Remove the two 10mm bolts DO NOT REMOVE THE TWO philips screws securiung the top of the box to the lower portion!!!
-On the MAF sensor, remove the two philip screws holding the MAF sensor to the box.
-Once the MAF is removed you can inspect the upper and lower sides of the filter. The filter MUST look dirty, as long as there are no tears in the pleats, press on and don't mess with it.

To clean the screen just just some shop air and blow out the debris. The more you stop in the screen the longer the life of your air filter!
Thanks to Compu85 for these pictures...Exactly the way it should be inspected and cleaned.

A Blocked screen may indicate approx 10-15" H2O, so be prepaired to clean the screen rather than replace the filter. If you see 25-30" suddenly you may have had water or snow ingestion, inspect the filter and determine a course of action. Either way start with inspecting your snow screen.

 

[Rub87]

so please point me to a good cone filter as I have no room for stock airbox in my car..

I shall post some pics from Apexi filter too =)





I now run an airbox from a mitsubischi carisma turbodiesel, it has a paper filter but it's quite restrictive, I measured over .1bar of pressure drop at high rpm, + I think it lets some very fine dust true as the inside of the pipe from airbox to compressor is always dusty, altough the dust if fine enough to not damage the impeller directly ..

 

[Bob_Fout]

so please point me to a good cone filter as I have no room for stock airbox in my car..

I shall post some pics from Apexi filter too =)





I now run an airbox from a mitsubischi carisma turbodiesel, it has a paper filter but it's quite restrictive, I measured over .1bar of pressure drop at high rpm, + I think it lets some very fine dust true as the inside of the pipe from airbox to compressor is always dusty, altough the dust if fine enough to not damage the impeller directly ..

There are several synthetic media cone filters from Amsoil, AEM and AFE.

 

[ChippedNotBroken]

I believe the air restriction on our cars is the exhaust, it would be surprising to hear that increasing the air intake capability would result in a material increase in performance. That said, I don't see the harm in lowering air intake resistance so long as filtration is not impaired. I read somewhere here on the forum about moving the battery to the trunk in order to make room for an air filter meeting that description.

For those running much larger turbos and chipped to run up to 6000 RPM I could see where the stock intake might start to become a limitation.

 

[T_D_I_POWER]

I use Hengst filters -Air/Fuel/Oil- for both of our Passats, and my other cars. This one is for the 04 TDI.







Here are the actual dimensions:
L X W X H = 9.500 X 7.875 X 1.875
A = 74.813 in2
V = 140.273 in3
No. of pleats: 87
L (calculated)= 163.125 in = 13.594 ft.
As (calculated)= 1284.609 in2 = 8.91 ft2

VS

Direct drop in K&N flat panel filter P/N 33-2125

Overall dimensions taken from the website:
L X W X H: 9.875 X 8.25 X 0.75
Actual (-.75/side for sealing): 8.375 X 6.75 X 0.75
A = 56.531 in2
V = 42.398 in3
No. of pleats:29 (from website)
L (calculated)= 21.75 in = 1.813 ft
As (calculated)= 179.438 in2= 1.246 ft2

As you can see from the calculations above, the OEM Hengst has greater filter media area, volume, and no. of pleats over the K&N. The greater the surface area of a given air filter, the better an engine will breathe and perform.

 

[Drivbiwire]

I believe the air restriction on our cars is the exhaust, it would be surprising to hear that increasing the air intake capability would result in a material increase in performance. That said, I don't see the harm in lowering air intake resistance so long as filtration is not impaired. I read somewhere here on the forum about moving the battery to the trunk in order to make room for an air filter meeting that description.

For those running much larger turbos and chipped to run up to 6000 RPM I could see where the stock intake might start to become a limitation.

Thats the point of using a manometer in my post above, there is NO restriction with the OEM filters even with performace tunes.

The OEM filter for a TDI has MORE flow capability (read larger area) than the filter on the Twin Turbo Audi S6 that can push north of 350hp and turn 8000 rpm.

The TDI already has a filter that is overkill in terms of flow, no amount of modifications can exceed its ability to flow unless you start adding cylinders to the motor, even then it can meet the demands of a V6-V8 turbo charged engine.

Also FWIW, the VW TDI filter has more area than my I6 and V6 CDI/Bluetec diesels pushing 220hp in stock form. I have the restriction data of those filters and at max power the total restriction at the turbo inlet at Maximum boost and full load is 3hPa!

 

[FlashT]

Originally Posted by Drivbiwire
Thats the point of using a manometer in my post above, there is NO restriction with the OEM filters even with performace tunes.

The OEM filter for a TDI has MORE flow capability (read larger area) than the filter on the Twin Turbo Audi S6 that can push north of 350hp and turn 8000 rpm.
<snip>

All of that is very interesting but I think there is an easier way to prove to everyone what works and what doesn't: Get a VCDS unit or OBD-II scanner, and take some mass airflow readings with the stock filter, K&N filter, and finally the cold air intakes(any brand). Intake air temp. should be measured as well.

By testing these filters and intakes in this manner, anyone and everyone can see whether or not these products work on their own car. I think
that some people continue to believe in this nonsense simply because it is nice to get something for nothing.

But in defense of cold air intakes, if one of these units really did increase the flow of cooler air to the engine, then someone who had smoke with, say, T4's might be able to use those same injectors with little or no smoke.

 

[Drivbiwire]

All TDI's already have a "Cold Air Filter"....whats the point?

Another aspect that is overlooked is the OEM intake point is drawn from a region of high pressure, if you defeat this you just lost 3-5 hPa of air pressure driving down the road.

Most after market filters are hardly "Cold Air Filters" in fact the majority suck in hot engine air from inside the engine compartment. They try to disguise the poor designs with vertical blocks and try to draw air from around a headlights but you are still drawing in from a lower pressure region of air.

Using a manometer inside the air box is the best way to monitor restriction. sure you could place a port at the turbo inlet but the difference in pressure would be minimal if any at all since they are both being measured in the same duct with the same pressure.

MAF readings will not tell you anything, MAF readings are not limited by the filter but by what is being commanded by the ECU. The MAF sensor only reads what the ECU is telling the turbo to pump into the engine...Don't confuse naturally aspirated concepts with forced induction...you will confuse yourself and the data that you are trying to interpret.

Again this takes us back to a pressure that is not dependent on any engine component, but is shows the net affect of the filtration and induction system, system being the operative word.

The bottom line is that a filtration systme is measured on two fronts:

-Whats the total pressure drop of the system as measured at the turbo inlet.
-Does the filtration system provide 10-15 micron filtration with 98% efficiency and still permit 60,000 miles between changes without any meaningful increase in restriction at the end of its service life?

 

[FlashT]

I understand what you are saying. I completely agree with you about filtration efficiency as well. There simply can't be any compromise. But is the pressure drop in the system pre-turbo the only definitive measurement that we can use to ascertain whether or not these aftermarket intakes actually work? In my opinion, the most important aspect to the induction system(pre-turbo) is the intake air temperature (as far as performance is concerned). And in this area, no intake system out there is as effective as the stock intake. It is the only intake I have ever seen that draws in air outside of the engine bay.

Again this takes us back to a pressure that is not dependent on any engine component, but is shows the net affect of the filtration and induction system, system being the operative word.

That is exactly what makes K&N, Carbonio, aFe, Spectre, etc. complete rubbish. And it makes me think about the turbocharger pressurizing the incoming air to 15 psi, at which point, it heats up. Then the efficiency of the intercooler is really what matters at that point.

So, in conclusion, it basically comes down to filtration efficiency with minimal restrictions coupled with a cool, positive-pressure air source that constitutes a good intake, right?

 

[Drivbiwire]

IAT has little to do with temperature with a total restriction of 5-10 hPa. There is so little energy spent to pull the air accross the filter that you are in the realm of hypothetical and surely not measureable by any means.

The largest pressure value you can measure is actual induction pressure (pre-turbo) and compare it to local pressure pre-filter. The difference between the two won't account for any measurable losses until you get to around 80+ hPa differential. Even with that amount of restriction the car will still make rated power the turbo will simply take a few miliseconds longer to reach specified boost pressure/flow.

If you want to have a good time with these cars, measure them on a dyno with a restrictor plate. Cut the intake inlet to 25% of it's original size and the car will still make the same power. In this case you may see a few degrees rise in IAT, but you could still debate whether or not its within the margin of error for the temp probe.

 

[velociT]

I'm glad to finally see a FAQ for this.

And I echo what Bob said. Some dry element conical filters such as the AFE or AMSoil perform well.

 

[Ben Dur]

ive read many of these arguements, discussions etc and personally analyzed the information presented, to the best of my sub-par logical abilities

my aftermarket cone intake system is on craigslist, and the stock air box (thank god i saved it for some reason) is going back in the car

im going to have to re-engineer the supply of cool (outside engine compartment) air as the dams etc that VW designed were not present when i got my car

 

[nicklockard]

Ben Dur, you should be able to source them from 1stvwparts.com or from a salvage chain.

 

[ChippedNotBroken]

Even if the filter is not a restriction, wouldn't the relatively small tube going down to the wheel become one at some point, or am i totally missing the point of the information provided by the manometer (which sounds like a totally awesome upgrade)?

Thats the point of using a manometer in my post above, there is NO restriction with the OEM filters even with performace tunes.

The OEM filter for a TDI has MORE flow capability (read larger area) than the filter on the Twin Turbo Audi S6 that can push north of 350hp and turn 8000 rpm.

The TDI already has a filter that is overkill in terms of flow, no amount of modifications can exceed its ability to flow unless you start adding cylinders to the motor, even then it can meet the demands of a V6-V8 turbo charged engine.

Also FWIW, the VW TDI filter has more area than my I6 and V6 CDI/Bluetec diesels pushing 220hp in stock form. I have the restriction data of those filters and at max power the total restriction at the turbo inlet at Maximum boost and full load is 3hPa!

 

[GoFaster]

Are you talking about the inlet tube for the turbo compressor?

This tube must inherently neck down to the same diameter as the turbo inlet, which is quite small. This inherently means that the absolute pressure will go down in accordance with the Bernoulli principle. Bernoulli pressure drops shouldn't be confused with frictional losses - but your simple manometer cannot tell the difference between the two. As long as the reduction in diameter is reasonably smooth and consistent, the reduction in pressure (because of the increase in velocity) will be in reasonable accordance with Bernoulli, and not greater than that because of frictional losses.

I know that for the Mk5 turbo inlet pipe, it doesn't look like one could do much to make it any better. I think the Mk4's had that "pancake" pipe going across the front of the engine to the turbo inlet. If there is a place where there is restriction in the system, that would be it. But still ... if the internal cross sectional area of that pancake is at least as much as the area of the turbo inlet itself, it probably isn't meaningful, because Bernoulli is going to dictate that the pressure is going to drop even more going into the turbo inlet anyway. I don't know how the cross sectional area of that pancake compares to the turbo inlet.

 

[ChippedNotBroken]

No, I am talking about pre-filter tubing.

 

[TDIMeister]

The OEM air inlet scoop, notwithstanding several sharp bends, is near a stagnation point of moving air, so that any incurred pressure losses are offset by positive pressure when the car is moving forward. Bernoulli's principle at work again.

 

[Ben Dur]

today the skis cleared up just enough for me to pull my little green TDI up to the garage to swap my crap cone filter with my stock air box

i first compared the size of these filters
by bending the paper filter around into a cylindrical shape
beside the cone filter it looks like this

as you can see the paper filter is significantly larger in all dimensions
it also has more pleads

this means the total surface area of the paper filter is significantly larger.
without actually measuring and doing all the math my guess is that its between 2 and 3 times the surface area of the cotton filter

i set up my wet/dry vac to test the flow differences
i was not able to reach the flow limit of either filter however

(yes i did this project on the ceiling)

with the vac ON
it pulls zero vacuum with nothing connected

and with my hand covering the inlet the vacuum pulls approx ~3in.Hg of Vacuum

next i hooked up each filter to the vac and tested each

each pulled 0 (zero) vacuum
both times the needle seems pegged right in the exact location the needle sits with no vacuum applied as well as the same amount pulled by the shopvac with no restrictions

finally i installed the stock air box


my conclusion
connected to a 5hp wet/dry vac neither the stock air box nor a cone air filter produce a measurable amount of restriction measured by my inexpensive equipment

 

[TDIMeister]

...
finally i installed the stock air box

Am I looking at something totally wrong or did you reinstall that airbox with the big gaping gash on the underside?

 

[Ben Dur]

it was my take on the "swiss cheese" mod

doesnt really negatively effect anything

its a larger area than the stock inlet
and given the car has none of the fresh air piping or dams that were provided by VW, it really doesnt matter...

 

[blackened]

The only other set ups I'd like to see tested would be something like the subaru wrx sti intake which is directly from a hood scoop pulling in quite possibly the coolest air of any system.

Another is something I've seen on camaros. The camaro system is a dual "cold air intake" that drops down behind the headlights. with our cars especially the 09 10 tdi we can drop the intakes into the fog light cavity. It would have more air forced in at higher speeds and would be sucking in very cool air from outside the engine bay.

and have the filters sitting in here

I'm not an expert and I'm not claiming that these are good options I'm just curious what some more knowledgeable people than I might say about these ideas.

 

[Ben Dur]

judging purely from your pictures i have to point out that the subaru is not pulling air from the hood scoop.

the hood scoop is pushing air through the intercooler...
if you look over on the passenger fender area you will see, that is where the airbox, maf, TIP, are located.

 

[GoFaster]

The Subaru hood scoop leads to the intercooler - that's what is on top of the engine with "STI" printed on it. I don't think the actual engine air intake comes from there, but I could be wrong - I don't know where the actual inlet is.

All air intakes that draw air from low on the front of the car or in front of the front wheels (on the underside) are vulnerable to sucking in water when (not if) the car is driven through puddles. The stock engine air intake on a Mk5 comes from the top of the grille near the center of the car and it leads first into a little box that's designed to dump water out the back while the air goes sideways, then into the airbox which again has an outlet on the bottom to dump out water. Aftermarket "cold air intakes" almost never have such protection against water intrusion ...

The TDI air intake is not a true "ram air" because the outlets for separating water are very significant, and will also dump out any overpressure. But, these cars won't go fast enough for "ram air" to have any meaningful effect anyways. But it is a "cold air intake" - the temperature IS significant.

 

[Rub87]

today the skis cleared up just enough for me to pull my little green TDI up to the garage to swap my crap cone filter with my stock air box

i first compared the size of these filters
by bending the paper filter around into a cylindrical shape
beside the cone filter it looks like this

as you can see the paper filter is significantly larger in all dimensions
it also has more pleads

this means the total surface area of the paper filter is significantly larger.
without actually measuring and doing all the math my guess is that its between 2 and 3 times the surface area of the cotton filter

i set up my wet/dry vac to test the flow differences
i was not able to reach the flow limit of either filter however

(yes i did this project on the ceiling)

with the vac ON
it pulls zero vacuum with nothing connected

and with my hand covering the inlet the vacuum pulls approx ~3in.Hg of Vacuum

next i hooked up each filter to the vac and tested each

each pulled 0 (zero) vacuum
both times the needle seems pegged right in the exact location the needle sits with no vacuum applied as well as the same amount pulled by the shopvac with no restrictions

finally i installed the stock air box


my conclusion
connected to a 5hp wet/dry vac neither the stock air box nor a cone air filter produce a measurable amount of restriction measured by my inexpensive equipment

Wouldn't it been easier to just take a lenght of clear turbing, fill it with water and use a ruler to measure the pressure drop..?