For my own K&N drop in air filter experience.
I used it on my last 2012 Veloster for several years. Also using brand name synthetic oil, follwing 6000km oil change interval (at dealer), permium gas, no hard pushing, only daily driving purpose and no moodification.
- no noticeable difference for performance and sound
- burning oil issue starting from around 78000km
- At 95000km, dealer promised to change the short block due to excessive engine oil consumption problem. About 1L per 1500Km. Under warranty cover.
- At 15000km, strange ticking sound appeared at engine and becoming louder. No more warranty for more than 100000km.
- Dealer and my own mechanic both told me it's internal engine problem and was needed to replace engine.
Finally trade in ASAP with the new 2018 ES turbo. When I asked them what is the main cause of the engine failure? They couldn't tell. Dealer said it might be manufacturer defective. My mechanic said it's the engine design issue as he also noticed abnormal engine noise for some Hyundai cars during the oil change service.
So the only thing I have done that might affect the engine directly is the long term use of K&N drop in filter for about 6 years. Surely, I did following the cleaning and recharge procedure for every year.
I don't know whether it's the real cause of the engine failure for only at 78000km and 15000km after the short block change. Yes, there are lot of reviews and reports from google about the con of this type of oil change high flow air filter. Trust or not.
I just don't want to take the risk again. So just want to share my own experience and it's up to your choice.