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


Our overall peak gains from both the drop-in K&N filters and the HPS Performance Parts silicone intake hose kit were exactly 7.1 horsepower and 2.4 foot pounds of torque. As you can see in the dyno sheet above, those gains were realized in almost every sector of our M5's powerband. Not bad at all from a simple filter and intake elbow swap that takes less than a couple hours to complete. 

An interesting point we must bring up is the effect heat saturation has on the E39 M5. It's normal for cars to lose power as they start getting hot, but the relation of power loss to oil temps did not line up with the losses we were experiencing on the dyno. Out of pure chance we happened to notice the OE intake elbows were getting pretty hot. After doing a little research we found that on the E39 M5 the intake temperature sensor was integrated into the MAF housing, which sits between the intake elbows and the airbox. Apparently the heat of the MAF housing leads to a higher than normal air intake temperature reading which causes the computer to dial back the power in order to prevent any chance of detonation. This is such a known issue that there are a couple of BMW specialists who offer kits to rewire and relocate the air intake temperature sensor away from the engine compartment (which you can bet we will be looking into and installing down the road). With our newly attained knowledge we decided to use one of our hand held dynoblower fans to cool off the MAFs in between dyno runs and just as suspected, power immediately went back up to normal levels. 


With the OE intake elbows we noticed our M5's power output would start declining after a handful of dyno runs. Unfortunately the intake air temperature sensor is built into the MAF housing which is very close to the engine and radiator. This causes the housing to get heat saturated, which in turns heats up the air intake temperature sensor and ultimately ends with decreased performance due to a false intake air temperature reading. 

With the HPS Performance Parts intake hose kit we did not experience the power losses we noticed with the OE intake elbows after running the car numerous times on the dyno. We feel this has a lot to do with the hard plastic of the OE intake elbows transferring the engine's heat to the MAF housings. With the HPS silicone hoses the heat transfer is nowhere near what it was with the OE elbows, as they serves as a buffer between the engine and the MAF housings. We can't say the issue has been completely eliminated, but the HPS hoses have definitely helped reduce the negative effects of BMW's faulty design.


In conclusion we are very happy with our current intake modifications. We surprisingly increased horsepower, while not experiencing any adverse effects. Since we are still using the complete OE airboxes the engine tone and sound has not changed at all. The gains we realized were not huge, but they were measurable and can even be felt with our butt-dynos. The car feels happier, especially on the higher parts of the rpm range. We can definitely sign off on the K&N filter and HPS Performance Parts intake hose kit combo for anyone with an E39 M5. 

What's next for Project E39 M5? We'd like to continue exploring options to improve our engine's intake system, especially since we know there is room for improvement when looking at where our engine is getting its air supply from. But, in our next installment we will be putting practicality to the side and looking into a new brake, wheel and tire package. You will not want to miss it! 





HPS Performance Parts



Read more about Project BMW E39 M5



  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!

Leave a Reply

Your email address will not be published.