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


The physical footprint of the filters is the same, but that's where the similarities end. (The K&N may look a little smaller in the picture, but it's due to it sitting further back on the workbench.) Note the condition of our OE filters. They only have a few thousand miles on them and are in very good condition, so any gains measured will not be from just switching to a clean/new filter.


Here we can see how dense the OE filter media is. Independent tests have shown that over time the K&N filters may not filter as well as OE filters. After looking at this direct comparison, it is easy to see how that may be true. There is significantly less filtering surface area with the K&N filters, but at the same time there is much less filtering area to restrict airflow.

Like any other vehicle modification, choosing a filter media comes down to application. OE filters are made with ultimate filtration and longevity in mind, which is perfect for a vehicle that is going to be driven a lot of miles between filter changes and in which performance is not very important. On the other end of the spectrum, we have the K&N filter which is designed for maximum airflow. The K&N filters still filter well, but know that you are giving up a little filtering prowess for increased air flow. You'd be amazed how much dirt/dust/rocks can get stuck in your air filters, more so with the oiled K&N filters than with dry paper filters. So be sure to check your filters often, they are not paper filters and require a little more care. Giving them a few taps will knock most of the gunk off. Do not use compressed air! I personally like to do this every few months or during every oil change on cars that are daily driven.


Installation of the K&N filters is the reverse of the removal. Lift the top half of airboxes and slip the new K&N filters in place. Then just lock the two halves of the airbox using the OE snap clips and you're all done.


With the new K&N filters installed we strapped our E39 to our MotoIQ Superflow dyno once again. As always, we disconnected the ABS computer inside the engine bay in order for the car to not freak out when only the rear wheels are moving. Since the last time our E39 M5 was on the dyno we've upsized from the OE spec tire size to Nitto 555-G2s in 245/45/18 up front and 275/40/18 in the rear. To ensure we isolate each modification and have comparable data we dyno'ed the M5 before the installation of our new K&N filters to get a new baseline.


Our M5's new baseline with its new Nitto 555 G2s was 286.2 horsepower and 272.3 foot pounds of torque. With the K&N drop-in filters peak power went up to 290.3 horsepower, for a gain of just a little bit over 4 horsepower. Peak torque did not go up, but if you take a close look at the dyno chart you'll notice there were torque gains across a large part of the power band, some as high as 6 foot pounds of torque (around 5,700 rpms).



  1. Hi Martin, and Mike,
    I love that fact you guys are doing a project E39 M5, as I’m working on mine as well. This intake article is very interesting, and would also like to see if you’d be interested in (dyno) testing another intake (AFE) that’s very easy to swap on. My E39 M5 came with it when I bought the car, and in design, it looks like it makes sense… very similar to the silicone hose + K&N setup you tested. Except, mine my AFE has a hard molded, smooth pipe and runs cone (K&N style) filters. Would you guys be interested in testing this setup as well? I am in Torrance, and the swap would take 5 mins. Please let me know if this is possible~

    *Reason I ask is, the AFE kit seems to have a negative gain on performance for the S62, based on an old dyno run someone did years ago. Looking at the design, I don’t understand how it could be worse than stock. I recently dyno’d my car and numbers weren’t bad. Wondering how it fares compared to your setup. -Thanks~

    1. Hi Joe,

      Thanks for reading! We’ve actually been wanting to test the AFE intake too. We’ll reach out to AFE to see if they would be interested in supplying us with one of their intakes for another test. We think that would be great info for the E39 M5 community to have!

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