Quote:
Originally Posted by verysideways
Yup, lots of things to watch for here.
1) BMW have refused to cover an engine failure on an M3 CP in the UK because of an aftermarket filter, which they said could have contributed to the engine failure. So yes, it does affect your warranty.
2) Oiled filters like the K&N do affect your MAF and will cause the MAF to fail earlier than it would otherwise. Maybe much earlier, maybe not that much earlier, but it will.
3) The stock air filter is every bit as good at allowing air through as a K&N. I have seen dyno results on multiple cars which prove this. The problem is that the stock air filter is replaced too infrequently. I believe it's every 3rd oil service, which is 60k miles or so? For the sake of £20, just replace the stock air filter at EVERY oil service. Maximum airflow, no warranty issues.
Look at the surface area provided by the stock airfilter - it's massive! It's very efficient WHEN IT'S CLEAN. Just replace it more often. It's cheap.
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This is very true, most people replace an old dirty oem filter with a new K&N and then report how the car feels more responsive! Most of which is because it's a clean filter, with a bit of placebo affect as well!
Same happens when people get new tyres, they say for example wow these Michelins are so much better than the Goodyears the car came with!