[hotrod182]

I was really skeptical about people claiming about 4-7hp gains with just a high performance after market air filter. But for $62, I figured, what the heck, being a curious one, I had to test one myself. I picked up my K&N filter yesterday. Hooked up the Gtech this morning and figured I would make 3 runs with the stock filter and compare them to 3 runs with the K&N. The results were kind of confusing at first, so in trying to evaluate any performance increases, I ended up making 15 runs today!

My first runs on the stock filter were disappointing. I figured the warmer temps, the tools in my trunk, and a good 6mph head wind were to blame maybe? My mph was in the high 107mph range. This was on a new batch of 91 octane, so maybe the car was adapting or something to the different gas? Also, I just had the oil changed this week. (9900 miles on the odometer). Sometimes the thicker viscosity of new oil will eat some horsepower. And my oil temp was usually above 230-240F in all these runs. My car runs best with the oil temp below 210F. So I figure all of these factors conspired to rob me of horsepower.

But the whole purpose of this test was to see if there was a noticeable improvement with the K&N. If the car makes more horsepower, I figure it would show in the trap speeds. With the exception of the 2nd to last run (too much wheel spin), all my runs were within .10 seconds. How’s that for consistency! I made 3 runs on the stock filter. The speed went down about .20mph on each of the 3 runs: (107.91mph, 107.73, 107.55mph). I immediately pulled over and put in the K&N drop in filter, and made 3 more runs. Quite to my surprise, the speeds were immediately in the 108mph range. And they got faster with each run! : (108.15mph, 108.56mph, 108.75mph). I thought this was simply amazing! I thought, well, the true test would be to put in the stock filter and make 3 more runs, showing the speed to go back down to the 107mph range. Unfortunately, that didn’t happen. The next 3 runs on the stock filter were (108.17mph, 108.62mph, 108.93mph). I then though, well maybe the car is just getting faster and faster regardless of the filter. So I pulled over again and put the K&N in for 3 more runs: (108.38mph, 108.28mph, 108.41mph). Okay. So I’m thinking no real improvement with the K&N. So to validate my thoughts, I pull over and put the stock filter in and make 3 more runs: (108.70mph, 108.20mph, 108.41mph).

So what do I make of all this? Not very conclusive evidence that there is a measurable difference through the ¼ mile with the after market drop-in K&N filter. The highest trap speed was actually with the stock filter (108.93mph). All these runs were on 91 octane. So 93+ octane, or cooler weather would surely put all these runs in the high 12’s. All these runs were in the 19” Generals with standard 35PSI in them. If the engine actually put out 6 more horsepower, you would see about a .50 mph trap increase.

Now if I were just looking at the initial runs after I put the filter in, I would be thinking “wow, what an improvement!” But being skeptical I wanted to back up the results. I think this may be what happens on a dyno. Just stopping the car, restarting it, different oil temps, tire temps, etc, might make a difference covering any realistic perceived performance gains from a product. And not being at liberty to make 15 back to back runs on a dyno would preclude you from making a definitive conclusion. Here is the log of the runs. You can see by the time stamps, they are all within about 3 minutes of each other. (Other than the 7 minute gaps for the filter changes).
I don’t know what to make of all this. I am wondering if the newly oiled K&N might be more restrictive right out of the bag till it dries up some? I will leave it in for now, and try and report back any other findings. Keep in mind, even though the stock filter seemed pretty clean, it was by no means new with 9900 miles on it.

[kingofqueenz]

so this basically told us absolutely nothing?

[catdog]

Originally Posted by kingofqueenz

so this basically told us absolutely nothing?

Are you kidding, it told us a lot: this particular filter seems to make little difference, so save your money!
hotrod, thanks for the extensive testing, i think its clear cut

[max boost]

Originally Posted by kingofqueenz

so this basically told us absolutely nothing?

:read thethread:

[kingofqueenz]

there is too much of a human margin of error between every single run, alil bit extra rpm at launch or whatever it might be will change the results drastically. a K&N filter will always flow better than a stock filter, and a gain in 3 or 4 hp will not be evident in a change of mph.

[max boost]

Originally Posted by catdog

Are you kidding, it told us a lot: this particular filter seems to make little difference, so save your money!
hotrod, thanks for the extensive testing, i think its clear cut

^^^^^^^AGREED!!!

the guy takes time to run and write the test and then u get an idiot like that....go and hang on a fiero board!

[sambonator]

Thanks HotRod!

[Driver72]

You know little changes are so hard to scientifically formulate.

As you all know, when I dyno tested I gained over 4 rwhp and 2 rwtq from the K&N drop in, and that was just in peak numbers.
From 4600-6100 rpms the K&N gained like 10-11 rwhp.

It definitely made the car breathe better.

However, recently Shiv dynoed the Dinan flashed car, and in an attempt to bump up it's dyno numbers Shiv and the owner of the car removed the airbox lid and dynoed that way. They reported no measurable power gains from doing so.

However, when Terry and I were dynoing a few weeks ago, we decided to remove his airbox too to see if there was any gains, and doing so saw like 8-9 rwhp more than with the airbox lid on.

Then a couple days ago when I was doing the mini-dyno day we were dynoing Deck's car with the twin cone air filter set up.
With the hood up on 2 runs he got ~355 rwhp.
Then we did a run with the hood down, it dropped to 345 rwhp.
So we thought that having the hood up in that case artificially inflated the dyno numbers. So we then did one more pull with the hood up again, but the numbers stayed in the mid 340's on that pull (however it was the 4th pull in 10 minutes so heat soak might of had an effect).


Bottom line, it seems like the tests vary.

In Hotrod's case, I'd have to say the K&N filter DID help him.
Notice the first 3 runs were in the 107 mph range.
These 3 runs were done when the car was the coolest and should of produced the best times.
Then he put in the K&N filter and suddenly got in the 108 mph range.
More air, better breathing, more power, better traps.
Sure, the following then were also in the 108 range, even with the stock airfilter, but did the ECU compensate at that point and lean the engine out regardless??

Who knows?

But when dealing with ~5 rwhp gains/losses, the slightest variables can change outcomes.
Heck, I've done dynos where my dyno results varied by ~5-8 rwhp on the same dyno, same day, same mods, same EVERYTHING, even letting the engine cool between runs so the engine temps are relatively the same.

It's hard to draw conclusions on something that will only add ~5 rwhp to a car making 300+ as it is.
But I'd say in the grand scheme of things, they do give a bit more power, but not enough to make any real difference in dyno or 1/4 mile times (especially in 1/4 mile times where driver AND car variations will also affect outcomes by .1 second and 1 mph easily between runs).

Thanks though Warren for contributing and doing the runs.
It's always fun none the less.
I look at it this way, if the K&N filters (and others just like them) DID NOT work, race car drivers and race teams the world over would not use k&N filters (and others just like them) in their race cars and personal cars either.
So they must do something, and as I suspect and tested, in our cars it's probably 3-5 rwhp on average depending on speed of the car and wind getting into the airbox.

[hotrod182]

Originally Posted by kingofqueenz

there is too much of a human margin of error between every single run, alil bit extra rpm at launch or whatever it might be will change the results drastically. a K&N filter will always flow better than a stock filter, and a gain in 3 or 4 hp will not be evident in a change of mph.

Do you know what CFM comparison actually is between the stock factory engineered filter (with much more surface area), and the oiled K&N, or are you just generalizing here? And in case you have seen the table, my launch technique is very consistant. Do you need to see my consistant 60' times too?. And again, this a stock filter with almost 10,000 miles on it. Although it isn't very dirty...here is a pic...

[catdog]

driver72 you make good points but is it worth messing with the oiling etc... i had a k&n filter on my e46m3 and it initially felt like an improvement then it seemed like it made things worse and eventually messed up the airflow meter. Ten again a 5 rwhp difference may not be measurable on 1/4 mil?

[hotrod182]

Yup, I heard about the guy that dynoed with no air filter at all, with no increase in HP no the dyno. That is kind of what led me to believe that there probably isn't any significant HP to be had in the air filter dept, or maybe the factory air filter is pretty decent to begin with. Did anyone ever read the factory literature on the air filter? Its kind of interesting.

Again, bottom line, is there are so many variables at work. Can you imagine trying to compare different dynos, 1/4 mile tracks, etc? Good luck! My first runs were definitely not with the car being cold. I had already been running all around town doing errands. My oil temps were already in the 230-240F range. I did however put $10 of gas in the car right before making the runs. (In which I used all that and more in these runs, LOL). So Driver 72, was your K&N fresh out of the bag when you installed it for the dyno? Does the K&N get more and more restrictive from the time that it is brand new? Or does the oil dry up some and make the filter flow more?? One thing that stands out is even after making a dozen straight runs..the trap speeds were much better than the first runs. Adaptation, etc..will always make it difficult to quantify minute power gains. As far as the DME still leaning it out from the K&N, I think it would be the exact opposite, the DME should do more enrichening with more air flow. Not necessarily the A/F ratio, but at least more fuel to keep up with the increased air flow. So putting the stock filter in, if anything should have been even slower with its supposedly more restrictive air flow characterisitcs. Again, had to analyze data like this with so many variables. But I am pretty satisfied that there is no significant gain if anything with the the K&N on my car.

[Driver72]

Originally Posted by hotrod182

Yup, I heard about the guy that dynoed with no air filter at all, with no increase in HP no the dyno. That is kind of what led me to believe that there probably isn't any significant HP to be had in the air filter dept, or maybe the factory air filter is pretty decent to begin with. Did anyone ever read the factory literature on the air filter? Its kind of interesting.

Again, bottom line, is there are so many variables at work. Can you imagine trying to compare different dynos, 1/4 mile tracks, etc? Good luck! My first runs were definitely not with the car being cold. I had already been running all around town doing errands. My oil temps were already in the 230-240F range. I did however put $10 of gas in the car right before making the runs. (In which I used all that and more in these runs, LOL). So Driver 72, was your K&N fresh out of the bag when you installed it for the dyno? Does the K&N get more and more restrictive from the time that it is brand new? Or does the oil dry up some and make the filter flow more?? One thing that stands out is even after making a dozen straight runs..the trap speeds were much better than the first runs. Adaptation, etc..will always make it difficult to quantify minute power gains.

No, when I dynoed my car stock air filter vs. K&N, the stock air filter had about 1500 miles on it, the K&N about 1000-1200 miles on it.

Yes, the oil does "dry up" a bit.
When you take it fresh out of the bag, if looks and feels oily (kind wet looking on the edges by the rubber).
After a bit of driving (say a few hundred miles, maybe more) if you take it out, it no longer has the "wet" oily look to it.

That MAY have something to do with it but I doubt it.
Bottom line is your car is making roughly 315 rwhp on the JB2 with 91 Octane, gaining 4-5 rwhp from a drop in filter will do very little.
That's a 1.4% gain in power.

The wind changes more than that.
Say on one run the biggest wind was 5 mph head wind, but then on the K&N run, you got 7 mph head wind.
That extra 2 mph head wind would negate the 4-5 rwhp the filter might have given you.

It's really hard to quantify such little numbers.
Look at the PROcede, JB2, Xede, etc.
There are SO MANY variances in what each car get's with them.
Some see 40 whp gains, others 50 whp gains.
We can't put a specific value on something that gives us 20% gain in power, much less a filter that might give us ~1% gain.

Look at it this way, for $60, if it gives you even 3 rwhp and gives you 1% better gas mileage, it was worth it.

[scooby9]

Thanks for posting up this info! I'll stick with stock until someone comes up with some insane K&N data!

[hotrod182]

Originally Posted by Driver72

No, when I dynoed my car stock air filter vs. K&N, the stock air filter had about 1500 miles on it, the K&N about 1000-1200 miles on it.

Yes, the oil does "dry up" a bit.
When you take it fresh out of the bag, if looks and feels oily (kind wet looking on the edges by the rubber).
After a bit of driving (say a few hundred miles, maybe more) if you take it out, it no longer has the "wet" oily look to it.

That MAY have something to do with it but I doubt it.
Bottom line is your car is making roughly 315 rwhp on the JB2 with 91 Octane, gaining 4-5 rwhp from a drop in filter will do very little.
That's a 1.4% gain in power.

The wind changes more than that.
Say on one run the biggest wind was 5 mph head wind, but then on the K&N run, you got 7 mph head wind.
That extra 2 mph head wind would negate the 4-5 rwhp the filter might have given you.

It's really hard to quantify such little numbers.
Look at the PROcede, JB2, Xede, etc.
There are SO MANY variances in what each car get's with them.
Some see 40 whp gains, others 50 whp gains.
We can't put a specific value on something that gives us 20% gain in power, much less a filter that might give us ~1% gain.

Look at it this way, for $60, if it gives you even 3 rwhp and gives you 1% better gas mileage, it was worth it.

I think a solid 5hp gain will be measurable in your trap speeds. Think about it, what is 1% of 110mph? 1.1mph. It doesn't calculate out that way though, it is usually about a .5mph increase that you will see with a 5hp increase. It should be measurable in the hp/weight/trap speed ranges that we are talking about here. Out of 15 runs, you should see some kind of trend. Again, lots of variables here, but out of 15 runs, it is not showing any definite trend. Obviously the sub 108mph runs are an anomoly. Seeing the promising results on the first runs with the K&N are what someone would normally get all excited about. But confirming the results by putting the stock filter back in kind of nullified that initial excitement. So what I would be interested in seeing is someone doing some flow testing comparing the stock filter to the K&N. That kind of lab data would dispel any discrepencies that people are having on the dyno, or trap speeds. The other variable has to do with real world driving vs dyno conditions. The intake air/under hood temps, ram air effect, etc, are slightly different at 100mph speeds compared to a dyno. On the dyno, an open cone filter under the open hood of a turbo car may show much more hp. But with a closed hood, high engine bay temps, an no ram air effect, the disadvantages on the road my be greater than the advantages on the dyno.

[sflgator]

Thank you for taking the time to do this hotrod182. Although similar to the K&N Air Filter, I wonder what the results would be with the BMC Air Filter?

I've been running with the ITG Air Filter, and certainly haven't "noticed" any difference (although admittedly, I don't think one would really notice +5-7WHP on a modded 335i ), but I ordered the BMC Air Filter anyway and am awaiting its arrival. I figured I'd give that one a try; if it's the same, I still have my "slightly used" oem stock paper air filter sitting in my garage.

[Terry335]

Very interesting testing hotrod!

Something else to consider is the air filter might be more of a benefit at lower speeds (with less pressure to help air across) than at higher speeds. That type of a scenario would help in 1/4 mile ET assuming equal traction, but might not show as well in trap speed. Were the K&N runs on average quicker in the 1/4?

[hotrod182]

Originally Posted by Terry335

Very interesting testing hotrod!

Something else to consider is the air filter might be more of a benefit at lower speeds (with less pressure to help air across) than at higher speeds. That type of a scenario would help in 1/4 mile ET assuming equal traction, but might not show as well in trap speed. Were the K&N runs on average quicker in the 1/4?

I don't think there is any definite trend on the K&N being quicker. I had plenty of 12.8x at 110mph+ runs with the stock air filter on 91 octane. I will however test again when I get some more mileage on the K&N. I can't tell you how invaluable the GTECH is in measuring increases in performance. Look how consistent the runs are. There is way more variance in day to day dynos or track testing. When you can run and test 0-60, 60' times etc, on back to back comparison, it really is very useful information. I was kind of disappointed with my trap speeds yesterday and thought something might be wrong with my car. So I decided to do some more runs this morning in 20F colder temps than yesterday. The oil temp never got above 210F this time. You can see the immediate improvements, and I am happy that my car is running to expectations now.

The one trend I am noticing is that my first runs are the slowest. In fact, you can see that the last 3 runs were only a few minutes apart, and kept getting faster and faster. Kind of the opposite of what I would expect. But interestingly enough, I have experienced the same thing at the drag strip.

Here are the results from this morning in cooler temps: Remember this is on 91 octane. I would bet the car would pick up more HP from using 93 octane than from the K&N filter.
(By using the R switch and higher octane, qtr mile drops to 12.60 @113.6 and 0-60 in 4.22 seconds on the stock air filter)

Note the consistency of the runs: All runs are within .07 sec in 1/4 mile ET. (60' times are within .061 seconds) So driver variables aren't a big factor here.

[Terry335]

Hehe I thought 12.9@108 was pretty good for an otherwise stock car... we've spoiled you with the R.

[MacDutchski]

Thanks for posting this up! 60 bucks I don't need to spend.

[hotrod182]

Originally Posted by Terry335

Hehe I thought 12.9@108 was pretty good for an otherwise stock car... we've spoiled you with the R.

I Know it can do better than that. Heck even at 2500 DA 87F Fontana, I trapped over 107mph. That was before I got the R switch. I can't wait till next weekend. With 30 degrees cooler temps, even at 1100Ft elevation, it should be a big improvement. I hope other 335i BMWs will show up, as this is the only open track day in months. (It sucks around here!) I will be so disappointed if it gets rained out.

[E90 335i]

Thanks for your time and contribution of this to the forum.

I was on the line between getting a filter or finding a true intake solution. I eventually got frustrated enough with the gain vs. no gain on a drop-in filter that I ordered a whole new intake unit and haven't looked back. It seems like that BMC filter is impressive -- at least we know it doesn't hurt.

[hotrod182]

I just read Shiv's post on the Dinan 335i dyno results. He also dynoed with the airbox lid off, with absolutely no improvement in HP. Maybe a small change in intake restriction does not really benefit our setup that noticeably. Hence, that may be the reason why the K&N is not showing any measurable increase in performance on my car. I KNOW one of the most important things for a good run is keeping the temps down. And even in 37F temps, I have absolutely no problem getting the same 60' times. So the higher hp at cold temps will more than offset a little less traction of a cold road surface.

Also, for those of you who didn't see my previous post on the GTech, it is a very well designed piece of test equipment. I took mine apart to inspect it. It has some very sophisticated circuitry. Definitely not a crudely designed unit.