Project E39 M5: K&N Filters and HPS Intake Hoses

by Martin Gonzales


So far, the goals for the modifications to our BMW E39 M5 project have been to enhance the performance of our ultimate driving machine without straying far from its original design or ruining its daily drivability. Will these goals always remain? Probably not, but before they change we're going to continue to extract every last bit of "no bad side effect" performance out of our M5. In this installment of Project E39 M5, we will test two very easy to install intake upgrades - the high flow K&N drop-in filters and HPS Performance Parts silicone intake hose kit. We will be doing individual dyno tests for each part to see if they will free up the S62's intake tract and yield some easy power gains. 

Although the E39 isn't the latest performance offering from BMW, it was produced at about the start of the new era when manufacturers started to really optimize the peripheral parts of their engines in order to squeeze every bit of efficiency (aka MPG) out of them. Modern vehicles intake systems are so well engineered that it's usually very difficult to find significant power gains from simple intake bolt-ons. Gone are the days of being able to bolt-on a well designed cold air intake and experience double digit gains.

The E39 M5 is no exception to this new trend towards engine efficiency since it was one of BMW's technical flagships at the time of its production. The E39's S62 comes with a short tract, dual intake system from the factory that seemed to be pretty high flowing. So, we were a bit skeptical going in about being able to find any real gains from just panel filters and silicone elbows.


The first part we will be testing will be a pair of drop-in replacement K&N high flow air filters. The M5 has an intake tract for each bank of cylinders to maximize flow so two filters are needed. The K&N filters drop right in to the M5's large dual air boxes with zero modifications needed. 

The K&N high flow filters are washable and reusable. They are also covered under K&N's bulletproof million mile warranty. On top of that, all K&N filters are backed by K&N's Customer Pledge. K&N will stand behind their products and will warranty costs caused by legitimate claims of any damage specifically caused by their filters. 


K&N drop in filters are made as a direct OEM replacement element that directly takes the place of the stock filter with no modifications or fuss. They are perhaps the easiest mod you can perform to any vehicle. But, will it perform as claimed and yield positive performance results? 


The K&N filter is pleated to give an increased surface area for more filter element in a given area, which increases its filtering potential. The stainless steel mesh surrounding the cotton gauze filter element is used for support of the soft fabric, especially when the filter element gets dirty and needs to be washed off. The filters can be cleaned with K&N cleaner and water, and then retreated with K&N filter oil to restore it to as good as new performance. The black polyurethane seal molded into the filter assures that no unfiltered air can leak past the element. 


The HPS Performance Products E39 M5 dual intake hose kit comes with everything you need to replace the OE intake elbows. They have a constant large diameter and are smooth internally to help improve air flow over the corrugated OEM hoses. The HPS hoses are made out of high-temperature silicone rubber, reinforced with 4 plys of polyester. This results in a stiff hose that won't collapse at wide open throttle.


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Tuesday, November 14, 2017 11:53 PM
It'd be fun to print up a dual air filter housing utilizing two 996 turbo filters. I'm not a fan of K&N from their filtration quality after being washed along with initial filtration. Along the lines of improving intake, have you considered applying the heatshield products sticky shield / lava shield on the underside of the intake plenum? There has to be a fair amount of heat to reject with that much real estate. Billy Johnson seemed to have good results on the Viper in this article: http://www.motoiq.com/MagazineArticles/ID/4272/Project-Viper-GTS-Part-7--HeatShield-Products.aspx I've applied it to my WRX to help reject cruising intake manifold temps. It works.
Wednesday, November 15, 2017 8:31 AM
On my 2005 Evo, the K&N drop-in panel filter was worth almost 8whp. Reduced the pressure drop through the intake by 1kPa which is big on a turbo car.
Martin Gonzales
Martin Gonzaleslink
Wednesday, November 15, 2017 10:11 AM
Bradl3y76: I would prefer to fix the issue by relocating the intake air temperature sensor instead of covering up the intake plenum with some sort of heat reflecting material. Though I'm sure it couldn't hurt to keep the plenum cooler the issue isn't necessarily that the air in the intake tract is getting ridiculously hot, it's the intake air temp sensor getting heat saturated and giving a false reading. Not trying to shoot your idea down, but I feel relocating the air temp sensor is a more precise approach to the heat saturation issue we experienced on the dyno.

I will say that if we ever decide to go forced induction we will definitely be looking at every possible modification that helps keep intake temps down, including shielding the intake plenum.
Wednesday, November 15, 2017 11:34 AM
Martin: Improving the accuracy of a sensor is absolutely a good idea especially if the ECU is able to properly correlate the changed values to the existing calibration, but I'm talking about actually reducing the intake charge temp. I remember Nowack performing the lower plenum heat shielding on S62 engines a while ago (has it been that long?) and the gains were double digit iirc. Furthermore, you can see results on another V8 http://www.superchevy.com/how-to/engines-drivetrain/1602-heatshield-products-i-m-shield-install-dyno-test-more-horsepower-for-less/. I think with the real estate of the S62 manifold plenum, it'd be a worthy mod.

spdracerut: I seem to recall their beta filtration numbers on the K&N media weren't too hip. I like more power, but when you see ISO numbers from a UOA go a bit crazy after using K&N, it really sours the experience.
Wednesday, November 15, 2017 2:48 PM
I'm surprised at the choice of K&N oiled cotton filters, especially with how sensitive the E39 MAF's can be.
Martin Gonzales
Martin Gonzaleslink
Wednesday, November 15, 2017 3:02 PM
@Bradl3y76 = Thanks for the link! Once I complete the sensor relocation and test some other intake options I will look into it. This way any future test data won't be skewed by the intake temp changes we may experience.

@sobe_death = Why so surprised? We've used K&N filters on many MAF equipped vehicles and have not had any issues. As a matter of fact, the K&N panel filters have been in our M5 for about 6 months now and we've experienced zero MAF related issues. From my experience the issues most people encounter are due to over-oiling their filters when they clean them. At least that's been my experience. When you have some time you should give this article a read:

Wednesday, November 15, 2017 3:13 PM
Martin, Totally welcome, I'd love to see the before and after results on the M5 and would be surprised if you can't get close to results like that.

Thanks for the good read.
Wednesday, November 15, 2017 4:33 PM
If you go down to the Cosworth filter description.

Thursday, November 16, 2017 4:53 AM
Nothing intelligent, articulate or technical to add. But I was thinking the same thing about the engine bay. The E39 (besides maybe a 2002) just looks bad-ass.
Kinda like the engine bay of a 288 Ferrari.
Thursday, November 16, 2017 7:21 PM
@Bradl3y, I've read the testing of the filtration of the K&N. There's always a compromise. I had one on my old Nissan for 130k miles or so that I drag raced, auto-x, and did a few track days in it. I also lived in Florida and Texas, so not particularly dusty places. On my Evo, I was only driving around Los Angeles, so not that dusty either.
Nate Aligood
Nate Aligoodlink
Friday, November 17, 2017 6:13 AM
This was the diy air filter study that I've seen done:


Also there are lengthy discussions on the M5board forums about oiled air filters and MAFs. I don't know what makes the MAFs in the E39 M5 unique, and it may just come down to people over-oiling the filter after cleaning, but there have been plenty of cases where people end up replacing MAFs and the general community consensus is that oiled air filters like the K&N are to blame. No problem in running them, just as long as you're aware.

I'd pick up a copy of INPA so you can tap into the factory BMW computer and check your additive/multiplicative fuel trims every so often as well as the air consumption numbers being reported by the MAFs. This will show you if the MAFs are degrading and would allow you to catch it before you start losing horsepower.
Friday, November 17, 2017 11:59 AM

I think the Amsoil filters, which use Donaldson's media, have a fantastic flow + filter ability. They've stopped selling drop in filter sizes, but the universal cone filters can almost always be adapted for each application. https://www.donaldson.com/en-us/industrial-dust-fume-mist/technical-articles/top-5-reasons-nanofiber-performance-layer-filter-is-worth-it/

Good stuff.
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