K+N air filter vs. Stock pressure drops

[lundgrji]

The following tests were performed on my 98 TDI NB, 51,800 miles, stock chip, ect..., 70 deg F, humid (90-100%), 1000 ft elevation.

Using a Dwyer Magnehelic 60" water vac/pres gauge I measured the pressure inside the air box, (clean side of filter) between the air filter and turbo. I used the existing fitting on the air box to attach the gauge.

Stock VW air filter had 4,500 miles on it, and K+N was new.
4th gear full power:
RPM Stock VW filter New K+N filter
2000 8" H2O vacuum, 7.2"
3000 10.8" 10.7"
4000 15.3" 14.5"

1st gear full power @ about 4400 rpm
20.3" 20.3

2nd gear full power @ about 4400 rpm
18.0" 17.7"

3rd gear full power @ about 4400 rpm
17.0" 16.5"

Results are the average of 3 runs each. A Wett-chipped TDI should show even greater differences with the increased air flow.
Also, a dirty paper filter will probably lose more flow than a dirty K+N.

Next, I checked the pressure inside the air box on the dirty side of the filter, between the filter and intake ducting inside the fender. I was expecting to see very little vacuum inside this area, since it should be atmospheric pressure, unless the inlet ducting within the fender presents a significant restriction. Tests were done with the K+N in place and same conditions as above. I used the small drain hole in the bottom of the air box to attach the gauge.

4th gear full power
RPM
2000 6.8" H2O vacuum
3000 11"
4000 14.6"

1st, gear full power @ about 4,400 rpm
20" H2O

2nd, gear full power @ about 4,400 rpm
17"

3rd gear full power @ about 4,400 rpm
16"

The results are surprising, with the inlet ducting presenting as much restriction as the air filter. It's like having 2 air filters in series. I plan to modify the existing ducting or add a second inlet hose.

To convert inches of water into psi, multiply inches water times .03613. To convert inches water into inches mercury, multiply inches water times .07355.

Given a max of 20" water, this equals .72 psi, or 1.47" Hg. With roughly 14.5 psi atmospheric pressure near sea level, that .72 psi drop is about a 5% loss of air density. This is about the same as being 1,500 feet higher in elevation.

And remember, these tests were done on a stock engine. If I get ambitious, I might check what the MAF screen is worth.

Some interesting observations:
Max pressure drop was always seen in 1st gear.
Bliping the throttle in neutral created about 10" h20 vac inside the air box.
The first run always gave the highest pressure drop. I assume the intercooler heats up, raising inlet temps, reducing power and boost and air flow. The difference was up to 3" h20.
Driving steady at 65mph showed about 2"h20 vacuum.

 

[SkyPup]

That is some pretty good investigative information and good data. Surprising that there is still that much vacuum in the intake tract way before the air cleaner, the diameter of the tubing must be the restrictive factor there. The K&N should be flowing quite a bit more cubic liters of air per minute than the stock OEM, resulting in the lower readings although the quicker spool up could have some effect on the readings. Anyway, interesting comparison.

 

[jrcanoe]

How about adding a 230cfm marine bilge blower drawing 3amps 12vdc to insure a positive pressure in the airbox most of the time. What would that due for perfomance and throtle response .

------------------
99 TDI Red Beetle
eyelids
FD. spoiler

 

[Peter Cheuk]

Is it possible that they designed the airbox to be restrictive so that the system would be forced to use that flapper valve at the bottom of the box to allow hot air in? If lundgrji were to bore a largish hole (1" or greater) into the airbox and redo the test, the information gained would be interesting, especially with the K&N filter.

 

[Ric Woodruff]

Looks like you are trying to separate the fly sh** from the pepper on this one. Had the stock filter been brand new, the readings virtually would have been identical, since they almost are already.

Thanks for the good research. Now I know to stick with the stock filter.

 

[GoFaster]

It's worth noting that since atmospheric pressure is about 400 inches of water, the measured pressure in the airbox is only about 5% of atmospheric.

What that means is, no matter what you do, even if you reduce restriction through the inlet duct and filter to ZERO, you can't gain more than 5%. The difference between stock and K&N is less than 1 inch of water in the worst case, that's 0.25% of one atmosphere ... bugger all, in other words.

I do believe that the performance of a K&N type filter doesn't degrade as much over time, plus they are re-usable, so I'll probably make the switch next time my car needs an air filter for those reasons.

I still think that the temperature of the intake air is more of an issue than the very small pressure drop across the filter. A difference of just 5 degrees F is a 1% difference in air density. In other words, keep the intake pressure drop down to make sure the flapper valve doesn't need to open. I'm sure the power loss that my car had because of that plugged screen had mostly to do with forcing it to draw hot air from near the turbo.

P.S. those measurements are really good info!! nice work.

Brian
'96 Passat TDI

 

[mickey]

Ric: You remind me of the Simon and Garfunkel lyric: "A man will see what he wants to see, and disregard the rest." Who will spend more money on air filtering over the life of his car: You, or me? My superior automotive understanding has led me to secure the most cost effective filtering system available. Get in the '90s, man! They're almost over!

-mickey

 

[SkyPup]

Ric, you ought to toss out your electric starter on your TDI and install a hand crank!

The electric starter sucks alot of electrons out of the battery by way of its high amperage requirements. In order to save electrons, you could remove the electric starter and install a hand crank onto the crankshaft. That way you will no longer be wasting electrons getting the engine cranked. Remember, a penny saved is a penny earned.

 

[Craig]

Won't work SkyPup. Can you imagine trying to hand crank an engine with the compression of the TDI?

 

[Ric Woodruff]

Mickey, relax! You remind me of the Metallica song "Misery": "...you take the weight of the world on your shoulders...".

Take it easy and enjoy life. Sit back and have a beer. You don't need to be rushing everywhere you go.

P.S.: Can you give me some information on those filters?, thanks.

 

[SkyPup]

RIC, those filters pass more CFM of earth's atomsphere through them than the standard OEM paper filters. Of course, the earth's atomsphere is composed of 78% Nitrogen so the effect is much more nitrogen is ingested by the poor little TDI after the air filter mod, probably something you'd not be interested in since it would result in your MAF signaling the ECU to tell the VP pump to inject more fuel through the varnished injectors pintle orifice. Of course, if you took your TDI to another planet in a different solar system with a higher oxygen content, it might be worth it to you in the long run economically. I'm certain a survey of the people on the Performance Forum would support that theory, some may actually even contribute to your cause.

 

[mickey]

What information do you want, Ric? I'll answer as if you know nothing about aftermarket filters:

The K&N, BMC and various other aftermarket filters don't use a paper filter element. They use a cotton element, sandwiched between layers of wire mesh to provide the required stiffness. The cotton itself only provides part of the filtering: It is also saturated with a special, "tacky" oil which traps dust particles. To look at one of these filters you wouldn't think they could be very effective filters since you can pretty much see through them. And it's true that without the oil they would be very poor filters indeed. But properly oiled they do at least as good a job as a stock filter at removing dust and dirt, and the filtering efficiency only gets better as they get dirty because the dirt itself acts as a filter medium. Of course, that's also true of a paper filter. But the oiled cotton filters provide so much better airflow than the stock ones that it takes 30,000 miles or so of normal use before the airflow drops to the level of a NEW paper filter. Then, you simply soak the filter with detergent, gently backwash it with a garden hose, wait for it to dry and then saturate it with fresh filter oil. You're then ready to go again for the next 30,000 miles. Total cost per recharge: About $5 if you use the standard K&N detergent and filter oil. You can see how the savings will add up over time. Properly maintained, the filter will outlast your car.

The only "unknown", in my mind, is the actual filtering efficiency. The manufacturers claim that, as I said above, the filters work better than stock. I'll be watching the "dirt" content from my next oil analysis very carefully to confirm that claim. But K&N has been making these things for a long time, they are standard equipment on multi-million dollar racing engines, and there is a huge body of anecdotal evidence to support their claims. Why don't the car makers use these things to begin with? Because they make the cars to be "idiot proof", and you require a certain number of functional synapses to properly use and maintain them.

Would you notice a power or economy difference? With a stock engine, I doubt it. I still think it's well worth the investment from a long term cost/benefit standpoint, but I have no doubt that the stock filters provide ample airflow for the stock engine. If you chip the engine, obviously the airflow demands will increase to match the extra fuel flow. I was able to notice an immediate seat-of-the-pants power and throttle response improvement when I combined the BMC filter with my Wetterauer setup. The stock filter simply couldn't feed the Wett chip all the air it needed.

K&N "Filtercharger" elements, made to directly replace the stock filter element in the existing airbox, can be ordered through any number of auto parts stores. The Checker/Shucks/Kragen chain stocks a few part numbers, and they should be able order one for you. If it's not against your principles you could also call Kelly Kay at Wetterauer and order a BMC filter element, which is an Italian-made filter that is virtually identical to the K&N. I have no personal experience with any of the other brands.

-mickey

[This message has been edited by mickey (edited August 26, 1999).]

 

[SkyPup]

Another thing that makes K&N air filters so damn good is that all their cotton is originally picked in DixieLand, way down South! Yahoo

"Rebel Yell"

 

[jrcanoe]

SkyPup what are you talking about; you live in that Yankee state below Georgia !

 

[Keith]

My TDI is non-chipped and the K&N filter delivers a worthwhile improvement in turbo response.

Keith.

 

[Craig]

I would think that the K&N would make a noticeable difference in any car. For example, the Suburban owner at work says that just the K&N on his stock V8 makes a 'big' difference.

Also on the TDI, smoke is = not enough air for the fuel, right? If so, and the K&N flows more freely, there should be a reduction in smoke (soot) on the stocker.

 

[tom]

I just got the K&N for my stock 98 Jetta. There is confusion as to the part number for the 98 (even at K&N!) It is the same as for the 97, 33-2069. I don't know about the 99 or 2000 model vw's. I have noticed a bit of a difference in quicker response but I'm just happy to have the longevity of it.

 

[mickey]

I used to use my Toyota for the same enourmous daily commute I now make in my Beetle. I tracked the fuel economy very carefully. (20.5 mpg like clockwork!) I installed a K&N Filtercharger, and did not notice any increase in fuel mileage whatsoever. No noticable power increase, either. I guess it depends on the vehicle, but I still considered it to be a worthwhile investment. I was going through a filter every month driving around on dusty contstruction sites. The K&N paid for itself very quickly.

-mickey

 

[Peter Cheuk]

Ric, you listen to Metallica?

 

[SkyPup]

Next thing I am going to investigate is installing a custom PCV pipe from the MAF to the turbo intake, it would be easy to form one out of some PCV tubing and get a little extra flow in addition the the K&N and the MAF screen removal.

 

[Peter Cheuk]

Skypup, won't work. I've already thought about that. The reason the hose has the ribbing on it is because the airbox is attached to the fender and the motor is mounted in very flexible motor mounts. If you use a rigid PCV pipe without provision for the flexing of the motor mounts, it will crack. Actually, that's the reason there's so much rubber in the intercooler pipe mounts and the large stainless braided downpipe.

 

[SkyPup]

Peter, I've got the K&N ABD Q-Flow on the rad Jetta and the air filter cone is mounted from the engine block, therefore I may be able to do it since it is all one assembly and not two separate ones. With the Q-flow the air filter, MAF, and engine are moving all as one. Thanks for the tip though, I have the K&N in the stock box on the NB TDI.

 

[Keith]

Skypup, thats a good idea to make the tubing less restrictive from the MAF to the turbo.

Here's my question: How heat resistant is PCV tubing? How much heat can it take underhood, before it melts?

Keith.

 

[SkyPup]

Keith, last time I fabricated something using PCV tubing, I took a propane torch to heat to heat it up gently until I could mould it and bend it into the shape I desired. I starts smoking after awhile, but I would say not until 350 degrees (don't put it in an oven to loosen it up, do it by hand). Boiling water is not hot enough to have any effect.
My only concern is where it attaches to the compressor of the turbo, how hot that part is, I haven't checked it yet there. The PCV should work though, as other things under the hood are made of polyethylene and polyvinyl thermoplastic, including the intake tubing the PCV will replace.

 

[mickey]

Y'all are mixing up your PCVs and your PVCs. (Too much PCP, perhaps?)

-mickey

 

[Keith]

At the compressor inlet, use a nitrile elbow. The elbow can open up into a larger diameter which you could attach the PVC tubing.

Keith.

 

[Darren]

Skypup,
PVC pipe will work for what you want to do. I'd suggest schedule 40. I ran PVC for an intercooler pipe for over a year with no problems(temps over 300 degrees F). I used the PVC originally as a funtional mock-up, and decided to see how long it would last. I finally removed it when I dumped the intercooler. Just leave a couple inches of hose at each end for flexing. Don't waste your money on silicone, unless it's for show. You can use radiator hose.
I have also used 2.25" copper pipe which is easily obtained and simple to solder. Spray it with some black crinkle finish paint and it looks OEM. Whether you will get any gain from the new pipe is another question. My experience with high power, turbocharged gasoline engines leads me to believe that you will not. One exception would be if you were also eliminating a 90 degree bend at the same time. By using two 45 degree bends, you can make significant improvements in airflow. All fluid pumping systems HATE right angles. BTW, I'm still anxious to see your boost control results(hint,hint;-)

Darren

 

[SkyPup]

Thanks Darren, The intake on the TDI is a corragated flexible plastic inlet pipe itself and thought that a smooth design would be worthwhile, certainly would look kewl in copper.
I have been working on my motorcycle the last two weeks in all my spare time installing a new centerstand when it was not designed for one. Ah wah, trial and error all the way and loads of soaking sweat out in the barn each night working with 85 degrees+, I was hoping that hurricane Dennis would blow in to cool things off a little, but no luck. Anyhow, the motorbike is back in action and this weekend, Labor Day weekend, I have some out of town company, however I still plan on squeezing enough time in somewhere to install that new VDO turbo guage I got into the TDI JETTA. From there, after i get some feel for the baseline circumstances of the Turbo Boost, I will give you a note to let you know that the boost controller is getting installed too. I appreciate you help and assistance with all this, I just have alot going on right now, plus it is still hotter than hades out around here, can't wait for this fall and hunting season to start. When that boost controller is ready to go in, you will be the first to know!

 

[GeWilli]

interesting - results in the first post - seem somewhat significant, No?

for those that don't always read the links posted this is an interesting introspective into the thoughts in '99

 

[Alek]

I was considering K&N because of some high end sooting and exhaust temperature danger. From what I see K&N gives some 0.25% to max. 0.5% gain (temperature gain included). This is in agreement with mine initial suspicion though not exactly same in cause. Today afternoon I made some calculations on pressure drops before filter. Pressure loss of individual air transport components tends to be equal and of order 2% each. I have PD TDI 115. This may involve some differences but from what I read not really much in principle.