So, tone can be hard to gauge in post so let me start off by saying I intend no offense or snarkiness in what I'm about to say ...
Thanks for taking the time to respond but your response is inappropriate for what I asked. I asked if Subie uses a standard size for all air filters. I did not ask whether or not you think using a K&N is a good idea. Having used one for 7 years in an Outback, 4 in an Impreza and many years in 4 other makes, along with my brother doing the same, I've never had a single issue with K&N. I tend to get a little better gas mileage with them in fact.
Now, because someone may read this thread and get freaked out by your "almost guarantee" comment without any justification, let me explain why that comment is completely inaccurate.
1. K&N has sold over 10 million air filters. No company could sell that number of filters if they constantly caused engine damage. Your "almost guarantee" doesn't even pass basic logic
2. There have been no class action lawsuits against K&N for any damage caused by their air filters - there would be if your "almost guarantee" comment was even remotely true
3. I contacted my Subaru tech at my dealership just to verify what I already knew. He's worked there for decades, has worked on every model and is well versed in the turbos. He owns many Subies and even races them. He stated:
- He has no issues with new K&Ns and they don't cause any issues
- He has issues with owners not following instructions on cleaning their K&Ns
- Instructions state that you must allow the filter to air dry COMPLETELY
- Some owners wait an hour and then apply the oil. Keep in mind oil and water don't mix.
- They install the filter and drive off. Because oil and water don't mix, the airflow knocks the oil off the water soaked filter and the oil goes into your MAF, etc.
- This is NOT a problem with the filter. This is a problem with the owner who refuses to follow clear factory instructions on recharging the filter
4. Here is a scientific research paper comparing OEM with K&N:
https://ac.els-cdn.com/S22120173163...t=1530315933_595b2edd821b11d0b0fbef3a1e7f7f92
Takeaways
- K&N is actually a little more restrictive with flow than OEM
- OEM filters better than K&N but researcher states that K&N would perform better in real world than how it was tested in research
- K&N gets better fuel mileage than OEM
- They did not test horsepower
- It's notable that the paper never mentions any chance of damage from using K&N
So why did I go through all this? Because it's irresponsible to make statements that are alarming and aren't backed up by facts. This is a forum where we all go looking for good advice. If you're going to make a statement like you can "almost guarantee" that using something is going to cause damage, then you need to back it up. I've backed up everything I've stated about the safety and performance of the K&N.
That all said, the filter for the Ascent is a different number than the one for the Outback on Subaru's site which likely means it's a different size. My tech also said that he runs OEM even in his STi, so that's given me some pause. I may or may not go K&N but regardless of the decision, it won't be because I'm afraid it's going to damage something.