I've used a Cosworth filter since my last oil change in November. So it has done about 3500 miles, and prior to that I have used K and N panel filters without any issues for this car and the previous impreza.
I was surprised to find fine dust on the maf side of the air box, and on the interior of the air box hose. The box was definitely closed properly, and I've never seen such poor filtration, but this was my first and last time with a Cosworth one.
The AEM dry flow replacement really felt an improvement, checked with bum dyno.
Anyone else unimpressed with Cosworth, given it is a throwaway item at £34 and also lets visible dust through, whether by poor fit or filtration?

 

Yep, after 5000 miles I had fine black dust covering the business bit of the maf and causing problems, fixed by cleaning. Not impressed.

 

Same! Had mine on for 3500 miles and was not impressed with the amount of dust that managed to get through..... Serviced yesterday with HKS filter so hope to see some improvement🤞

 

I’ve been using the genuine STI performance air filter (ST165464S000) on my JDM. A bit pricey, but it works really well

 

That's good feedback that it's not just me. I thought that I would try Cosworth after reading about oiled filters and MAF sensors.
The Sti filter has the usual Sti tax!!

 

That is true unfortunately. The Sti filter is about £70-80 or so; about double the price of the Cosworth filter. Then again a new Subaru MAF sensor is well over £200 and an engine repair bill would be considerably more.

 

There's been loads of auctions going with cheap cosworth parts forsale. And the price of Cosworth filters has dropped alot. I buy the Subaru Pro R filters made by Pipercross. Seem to work well.

 

I only use std OE filters in the std airbox, most so called performance filters, are doing very little in the way of filtration, the last Cosworth one I looked at you could see through it.

 

I stick with standard ones myself or ones Subaru branded.

 

Good to know, I'll avoid these.

 

Would you happen to have access to the Cosworth filter that you claim to be able to see through by any chance.

Only im looking at a new Cosworth filter through my window with the sun blaring and i cant see **** all through it.



Im just wondering if the "cosworth" filter you had may have been a copy?

Siv

 

I think you'll find he saw it in one of the numerous engines that he rebuilds. Google Finch Motorsport!
I started this thread simply to warn people what I found . It's the only time it's happened in 10 years of Impreza ownership, and the only Cosworth filter I've used. I bought it from IPC. I do live down a dusty tarmac track, but I did when I had a k and n with no issues.

 

You say you were surprised to find dust in the air box, Why?
It had been in your car for 3500 miles and repeatedly used in dusty conditions...
The oil on the K&n filter would probably have collected all that dust previously.

Yes, I’m aware of Finch motorsport, I was at Chevron when Bob Rawle told me Simon was rebuilding his engine.... built by Finch Motorsport.

From what I can see the Cosworth is a perfectly good air filter.

Siv

 

Come back when you have used one, rather than just purchased one, and hopefully you won't have any problems.
I'm not sure what your point is asking me why I was surprised; it's an air filter, which didn't filter, unlike the other ones that I have used. That surprised me, and I thought it was worth sharing. Then I found I wasn't alone. And in admiring your car on your thread, I thought it was worth repeating, given the 2.5's sensitivity.

 

Given the fact that you deliberately omitted from the original post that you drive up and down a dusty track changes the whole dynamic of the thread IMO.
Now that we have the facts people can be routed here during a search and make a more informative decision.

Thanks,

Siv

 

The track is tarmac. It is 300m long. It wasn't dusty in the spring when this happened. The other brand of filter did not let visible fine dust through during last summer's drought.
I'm sticking with an air filter that is fit for purpose, and not throw-away, which is cleaned and checked every 3500 miles...far in excess of the recommended intervals.
When you've actually used yours, and it has performed faultlessly , I will be happy for you.
Btw, you can't see light through a AEM or K and N like you can in your photo of a Cosworth one.
So come back in a few months with a valid experience and add to this knowledge base instead of jumping my thread when you haven't used one yet.

 

My criticism is constructive and beneficial to current and future users of the Cosworth filter, I don’t agree with everything you say, oh dear, how sad, never mind.
May I remind you dear sir that this is an open forum and I have as much right as you to post on your thread.
Just because I don’t agree with you doesn’t mean I want to argue with you, don’t take it personally.

This filter has been endorsed by Thwaites and Engine Tuner, two of the most respected tuners amongst the Subaru community who have both had zero issues with Cosworth.
I will use it in good faith on their recommendation and report back.
I will also never be bullied or deterred from expressing an opinion on here or anywhere else in fact.

Back on topic.

Three people have complained about the filter on this thread, did any of you take a before and after picture of how much dust was in the air box and on the maf?
Was the air box and maf completely free of dust before the Cosworth filter was fitted?

Anyway, like I’ve said, please don’t take it personally.

Siv

 

I should have taken a photo, as it was very visible. I do oil and filter myself, every 3000 to 5000 miles.

 

I've had similar experience to Hedgecutter - Cosworth filter after 5000 miles coating the maf in a fine black powder. Not really fit for purpose in my opinion. Won't be using again.

 

.. ??

 

Absolutely clean. I had to take the air box pipe off as well, and I could see it continuing into the turbo intake. My only interest is my car's health, and I bought the Cosworth because I'd read about maf oiling with the K and N. I've done 31000 miles with this car, and posted because I was so shocked at the amount of dust.
The only other possible cause could have been incorrectly securing the airbox lugs and clips; the reason that I began my own oil/filter changes was because a well known home county Subaru specialist failed to do this on my old blob wagon, so I am particularly fussy about making sure it's closed correctly.
My lane being dusty isn't relevant, as the other filters have had to perform under the same conditions.
There's no doubt these filters draw well, but to pass bigger dust particles, the weave has to have bigger gaps in it.
I suspect Siv and I both bought the Cosworth for similar reasons, and there's always the chance that my AEM may be poor as it is a dry filter. I'll let you know in a few months

 

So it would be fair to assume that any “performance” air filter, panel or induction kit, by it’s free flowing nature is more than likely going to allow fine particles through.
I don’t know what the answer is then

Siv

 

Agreed. I'm on the train to Enginetuner at the moment, where I've had a full health check with compression and bore scope tests ( not because of the panel filter!) and all was good, so I think regular maintenance is the key. Anyone who lives in a urban non dusty environment will be fine, I'm sure.

 

Agreed.
For the cost and how easy they are to change it’s a no brainier to swap it out every few months.
Plus you have a healthy engine so whichever way you look at it the k&n, cosworth and aem filters have not damaged your engine !!
Thats good news.
Have a safe journey.

Siv

 

This is making sense now with a few niggles I have had with my Gen 4 JDM Legacy.

 

Hi all, have lived in Spain for the last 3 years and took my Sti with me. Have had a Cosworth panel filter in it for 2 years as I don’t do many miles a year. (just about to change the filter). Opened the cover and there is no dust whatsoever on the MAF side of the filter. I live in Seville where every day my car is covered in fine dust that finds its way into every part of the car. So just wanted to make some of you feel less stressed about the whole thing - The filter has without question on my car done an amazing job. Ade

 

Great stuff.

 

Great feedback

 

Living a life free of rain and salt!

 

Thanks for the feedback, Lovely blob BTW.