When I was in college 10+yrs ago, I had an accord that replaced the stock air-filter with a K&N permanent filter. It wasn't a dramatic increase but an increase none the less especially at higher rpms. It was wondering if anyone had any experience with fitting these in a '07 328i or any BMW. Would it void the 3yr/60000 warranty or damage anything. I realize cars made today are predominantly computer controlled so changing something like how much air gets into the engine might throw off its normal calculations causing strain on another part of the engine. Again i might be totally wrong. Anyone have any advice, it would be greatly appreciated. I the reason i was thinking about this is because I heard better air filters do give you better fuel economy and better performance. Thanks, idoc328
You probably wouldn't feel any difference. On the E46, Dinan claims K&N stock replacement yields a few horsepower with his basic software - don't know if that's available for the E90 cars. By the way, you have a 4 year/50,000 mile warranty. Dealer may not like an aftermarket air filter, but unless you get crud in the intake system, it shouldn't effect the warranty. A stock K&N replacement won't set off error codes - don't know about cold air intakes that suck in a lot more air - depends on software i suppose.
It's not just the "crud in the intake" that you see, but the micro-particles that get by and into the combustion chamber that might ruin your rings. This debate is ongoing on the Internet and I have nothing against K&N, they've been around a long time. The facts are it could void your warranty if you have in internal engine problem, the benefits are minimal if any, and no one makes as good a micronic filter as the BMW OE suppliers. (245,000 mile '87 535is w/Dinan software and stage 3 suspension, but with stock air filter element always!)
K&N OK, aFE Better In response to this thread, I have an E90 '06 325i that I plan to keep until I die. I love this car and with that said, would not want to do anything to harm it. I've used K&N stock replacement filters in the past and have had good results and have confirmation from my local dealer that they do NOT void the car's warranty. With this car, I was looking for something a little more special, so I kicked in for the aFe Cold Air Intake. This set up replaces the complete airbox, filter and intake tube. The new setup includes the filter, heatshields, smooth intake tube (vs. stock flex tube), gaskets and seals. It took about an hour or so to install and the difference is dramatic! The power and response is much improved albeit with an increase in intake noise. Hearing six cylinders sing is a joy though. The system even included a "Pre-Filter" which looks like a porous cloth shower cap for the filter element and acts to block larger debris ie. bugs, stones, etc. A couple words of caution would be to pay close attention during installation to seal the system completely such that all incoming air is directed through the filter element. I went so far as to have the entire installed assembly leak tested to assure that there were not any vacuum leaks letting unfiltered air into the intake plenum. Another caution is that cold air intake filters do need to be cleaned more often as they are more exposed to the elements than the filter in the standard airbox. As far as the warranty goes, I'm pretty sure this system is not compliant, but I am capable of putting the stock system back on if need be. So far I have not had any bells, whistles, lights or alarms go off because of this either. My previous experience with cold air intakes is with my old E30 325e, which has had a K&N Cold Air intake installed for the last 12 years and is still going strong with over 300k on the clock.
