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John V.






BMW Air Intake, K&N Air Intake


Dear Gil, I recently completed installation of a K&N Air Intake system on my BMW 05 325CI. While I was doing the installation I replaced my DISA valve as well as my lower Intake Boots. I also replaced my MAF with a OEM. Prior to all this I was getting a Code# PO 174 AND PO 171 and a check engine light after 10 miles of driving. I did find a crack in my lower intake boot and was replaced. Today the codes are gone and the Air Intake system from K&N is working fine. My question is: “Is it really worth it to get a aftermarket Air Intake System? Thanks JV in Apopka K&N Cold Air Intake Kit: High Performance, Increase Horsepower: 50-State Legal: Compatible with 1999-2005 BMW 3 Series (325Ci, 325i, 325 Xi, 323 Ci, 323i, 328Ci, 328) 2.5/2.8L L6,57-1002 : Automotive


Hello Mr. John, this is a multilayered question, I’ll try my best to be clear with the answer. The short answer is usually with this type of intake system the answer is no. The first reason: K&N filters are what is called a wet type filter, you are supposed to clean them and spray them with a lubricant afterwards. The issue is the lubricant. The air mass meter is an exposed, heated wire, as the air passes by the wire it will cool it down. The engine computer will always keep the temperature at the wire at a predetermined temperature. The amount of amperage that it takes to heat the wire to that temperature is what tells the engine computer how much air is going into the engine in order for it to have an equivalent amount of fuel. What happens is the lubricant from the filter, along with fibers from it will get on that wire, causing the resistance to increase. That will cause a false air reading as the engine computer will now have to use more amperage to heat the wire, therefore making it think that there is more air going into the engine than actual. This in turn will cause the engine to run “rich”, or too much fuel for the amount of air actually going into the engine. When that happens the only solution is to replace the air mass meter. There are products that claim to be able to clean the sensor, however, they are not effective.

Now for the second part, expected gains for a naturally aspirated (non-turbo) engine with what is called a cold air intake will be between 2 and 6 HP on average. The intake system you have is not the cold air type, this type of intake system will move the filter out of the engine bay. The reason for this is engine bay temperature. While the factory air box does restrict flow to an extent, it also works as a heat shield for the filter, aftermarket heat shields tend to not be as effective due to their open design and/or material. This causes the engine to actually ingest hotter air than with the factory air box, as hot air is not as dense, the result is less and hotter air going into the engine. These types of intake systems have been found to actually cause the engine to lose a few horsepower. The other factor is the actual design of the intake pipe, it has to be very precise in design, it cannot cause any turbulence inside of the pipe near the air mass meter as this will also cause erroneous reading. The downside to having a cold air intake is the fact that it will make the engine more susceptible to ingesting water if you go through water. It will usually place the filter on one of the lower edges of the bumper, and as we know, puddles are common in this area especially this time of the year.

I hope I was able to answer your question without boring you too much. Please let me know if you have any other questions. Thank you.

Gil Neves


This Post Has One Comment

  1. Gil, I cannot thank you enough!
    The K&N Intake System I installed is a huge upgrade to the cheap boots and hoses that were stock. I used NASA grade clamps and made damn sure the MAF is tight on. On the filter itself, yes.. its exposed to the elements but I have installed a K&N micro fibre netting over the filter that is good for 2 years. I also upgraded the rubber ribbing K&N uses around the steel plate replacing the BMW Stock air box. I’m getting a nice low decibel rumble out of the exhaust and a nice burp of air when engine turns off. Now I’m considering a turbo pump. So far after more than a year, no warning lights and no further problems. I may be just another sucker for K&N but it is a proven on the track product.
    Thanks so much

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