Project E90 M3: Part 5 - K&N Filter Cover

Project E90 M3: Part 5 – K&N Filter

by Billy Johnson

We gave our M3 a quick and easy bump in power by swapping out the factory air filter for the industry-leading High Performance K&N air filter.  We have seen some impressive gains from K&N products and feel there’s no reason you shouldn’t have one on every car you own!  But how much power can really be gained over the OEM BMW air filter in this highly stressed and finely tuned 8,250rpm screaming V8?  Read on to find out!

I can’t say enough about K&N products or them as a company.  I have used their filters for decades on everything from go-peds, scooters, motorcycles, cars, trucks, and racecars.  I’ve always felt a performance increase and have never had an issue or negatives whatsoever from using their filters.  Due to their quality of construction and ability to be cleaned and re-oiled, K&N filters have outlasted my ownership of each vehicle.

K&N is so confident in their products that on top of the K&N Million Mile Limited Warranty, they have an unbelievable Consumer Protection Pledge:


K&N Consumer Protection Pledge

"We want to make sure that when you buy a K&N Lifetime Air Filter or Air Intake System, you can be confident your vehicle's warranty will not be impacted.  We also want you to feel confident that even if you experience a difficult dealership, we will step-in and resolve the issue, so you won't have to.  Therefore, we make the following Pledge:

K&N pledges to our customers that they will not be taken advantage of and charged for a repair due to a dealership warranty denial blamed on the presence of a K&N product."


If that doesn’t give you the confidence to buy their products, even for your brand new car under the factory warranty, I don’t know what will.

At MotoIQ we like to dispel myths and give you the most objective and scientific data possible through proper back to back, A-B comparison testing.  To continue this trend, we headed back to our friends at Power by the Hour in Boynton Beach, FL to turn the drum of their 2,000hp capable Dynojet 224xLC.  PBTH is known for modifying Mustangs with everything from bolt-on supercharger kits to in-house developed turbo systems, suspension, brakes, fabrication, and dyno tuning.  They are such a pleasure to deal with and we really like the consistency of their dyno.


Project E90 M3 on the Dyno PBHUnfortunately in Florida, 6 months out of the year is less than ideal for producing bragging-rights dyno numbers.  Rather than waiting months for the temperature to cool back down, we decided to go ahead and do our A-B testing of the K&N filter in the heat of summer.

With ambient temperatures in the high 90’s to triple-digits, brand new Continental ExtremeContact DW tires (which weigh more than old worn tires) and different wheels, we knew that we were not going to see the same power that our car made in the low 70’s with 0% humidity.


Project E90 M3 Dyno Pull Baseline HOTDespite an early morning arrival, the intake temperature were reading 96*F with 44% humidity.  Our M3 put down 349.56hp and 271.49lb/ft of torque.
Project E90 M3 Baseline Hot dyno Pull vs cold BaselineIf you’re familiar with Project E90 M3, you would know that our M3 put down an impressive 379.76hp and 276.63lb/ft of torque.  Other than the new wheels and tires, everything else remained the same, including the use of Mobil 1 0W40 motor oil.

The power and torque were even in the mid-range from 3,000-5,000rpm and a separation in power starts at 5,000rpm and increases all the way to redline.  Since high compression, high revving engines are sensitive to temperature and pull the most timing at high rpms to avoid knock, this 30.2hp and 5.14lb/ft of torque loss was likely caused by the 25*F hotter test conditions and 44% of humidity.

Despite weather not being ideal to compare to our previous dyno runs, as long as do our back to back testing under the same weather conditions, we should have a valid comparison test.  This is why baseline testing is important and it’s difficult to compare dyno runs on different days (or even the same day if the weather changes significantly), let alone different cars with varying wheel diameters, the model of the tire, how old the tire is, motor oil, final drive ratios, etc… 

Because of this we try to keep the variables down by using the same oil, same tire, and usually we do a good job at ensuring the weather conditions are as consistent as possible, but this article was purely for an A-B test of the K&N filter and we didn’t want to wait until winter just to see peak numbers above our previous 379.76hp pull –which will happen once the weather cools back down.


Project E90 M3 AirboxThe 4.0L V8 has eight individual throttle bodies (ITB’s) under that massive intake plenum which is fed by a large, oval intake tube that connects to the airbox housing a round air filter element.
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Wednesday, August 17, 2016 2:09 PM
After reading this test, I will not be using K&N filter on my car.
Wednesday, August 17, 2016 5:13 PM
Basically a 5 page advertisement for K&N, wow.
Wednesday, August 17, 2016 8:29 PM
That test confirms that K&N is nearly 97% efficient while being almost 300% less restrictive than the 99% efficient filter. On the vehicles that I use, that is more than a decent compromise considering the average power gain.

Honestly, you probably shouldn't use a K&N if you are doing rally or off-road events. But considering how little dust accumulates on the highway and street, I don't mind taking the chance on my car for a proven power increase. My car is not pristine or babied in any way, it's meant for driving and its meant to be used in the real-world.

BTW, the particulates that build in your intake from unburned hydrocarbons are pretty big particles and for some reason or another they don't seem to affect engine operation.
Wednesday, August 17, 2016 10:05 PM
@cmh, except there's actually multiple points of data on multiple platforms. I had a K&N on my old Nissan SE-R for over 100k miles.

On my 2005 Evo, I did a drop-in K&N and datalogged a gain of 1kPa of pressure in the airbox at the top-end of a 3rd gear pull. My memory is a bit hazy, but a K&N filter on an Evo 8 would routinely improve power 6-8whp on an otherwise stock Evo.

For reference, I need to be going about 100mph for the ram air duct on my S2k to register a 1kPa gain.

@Samuel, I've read that filter test before. If I lived in a very dusty/sandy area, I would use an OEM. But for many places, most of the US I'd say, the K&N is perfectly adequate IMO.
Thursday, August 18, 2016 6:01 AM
I don't think Samuel even read the article, or K&N's warranties:

"our warranty covers any engine damage or related costs incurred as a direct result of the use of a properly installed and maintained K&N O/E automotive replacement air filter or intake system"

So if anything were to happen to your engine from a lack of filtration, they would pay for it. Can't beat that.

No company warranties products for off-road or racing use, however K&N is used on top level of motorsports world-wide (off-road, on-road, water, air) so I think they know a thing or two about how to filter dirt in the hardest environments...
Thursday, August 18, 2016 1:57 PM
Strange that a V8 would suck air from a centralized point, or is this more common than not?
Thursday, August 18, 2016 5:11 PM
@Matt, it's actually more common than not. I'm actually having a hard time thinking of a V8 that does NOT get air from central point. I think every GM LS has a single throttle body, Mustang, Dodge... off the top of my head, only V8 I can think of that has individual plenums is in Ferraris.
Thursday, August 18, 2016 6:05 PM
@stuntman, Yes I read the article. Sure the normal costumer is never gonna use a k&n for 200k miles, check the valve and ask K&N for a rebuild.
Show me the SAE test from K&N that evaluate their filter.
Thursday, August 18, 2016 8:10 PM
SuperPro warranty covers off road and race use.
Friday, August 19, 2016 11:14 AM
@spdracerut, Some V8's have multiple paths from the throttle body... STS-V comes to mind, though it does still run into a single filter.

One thing I did see in that test is that the K&N's restriction goes up exponentially, so I wonder how the power gains compare at 40k to an OEM at 40k. Looks like the K&N could actually be worse at that point, but then again that's just when you'd clean it, I guess.
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