Quote:
Originally Posted by Hejnfelt
I can chime in here with a lot of experience from motorcycle racing and tuning over the past 20 years.
Engines running K&N Cotton Gauze filters get wrecked fast. Particularly it's the cylinder liner that gets shredded and both liner, piston rings and piston lifetime is compromised. This is especially true in countries like Estonia where 5 months of the year every car drives on studded tires creating a serious amount of very rough and sharp road dust that accumulates in the snow and ice which then settles in crevises of the streets where it doesn't clear out until well into June after springtime rains.
In the N54 that's notorious for blow-by just imagine how much debris ends up in your oil and eventually coating every surface in the engine. Obviously these engines are pretty tough and you're unlikely to see much day to day difference, but reliability of the troublesome components like Vanos or PCV Valves will be more likely to fail. Particularly the Vanos system should be of concern as debris in that system can rapidly lead to oil leaks between the steel cut O-rings inside the cam phaser system and that's a common and expensive repair.
Cotton Gauze filters have their place but in the majority of road cars they cause much more harm than good, especially if you're chasing performance as most of us want performance in combination with reliability but with cotten gauze DCIs your reliability is shortened significantly.
It's a shame that filter technology isn't progressing in the regular market and is really only concentrated at the higher end of cars. What UFI is doing with the Porsche tubular filter system is pretty cool and I would love to put such a setup in the Z4.
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Like you I used K+N filters on my bikes for many years..I never wracked that many miles on them so wear was not obvious.
I intend to keep my 35is for a very long time so longevity of the engine is a concern..hence why I went down trying to avoid any modifications to the very good stock air inlet system..hopefully my Mr.5 version will still offer pretty good filtration…
I drove back yesterday some 2 hours and 70 miles with the VSRF DCIs fitted and it confirmed my prejudice against DCIs based on inlet noise as well..
So Mr.5 being refitted this morning.