Quote:
Originally Posted by jmillet
Per the BMW NA Service Maintenance Checklist for your Z4 replacing the intake air cleaner element (AKA air filter) is an Inspection II item which translates into about every 40,000 miles. The checklist does say:"Reduce replacement interval in dusty operating conditions"
Best practice is to open up the air box at every oil change and examine the filter. Clean all the debris out of the air box and vacuum off the filter. If the filter is still showing signs of being dirty then replace it. I'd stick with the OE paper filter P/N 13 72 1 744 869 that will run you $13.78 from Autohaus AZ.
Don't forget about the cabin filter P/N 64 31 6 915 764.
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What he said.
It's just folded paper with a plastic frame. It would last 40 years if you only drove 1000 miles per year. K&N are not recommended because the oil can foul the airflow meter and cause problems. The factory paper filter is just fine. If they could have claimed 5 or 10 more HP by changing the paper filter, with all the millions they spend on engineering, don't you think they would have done so? It's not the limiting factor in airflow or HP for the engine. Dyno testing with different filters or no filter at all indicates no difference in engine power.