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Not all paper air filters are equal.....

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#1 Blastertrev

  • LocationSunny Cumbria (NOT)

Posted 23 May 2016 - 08:45 AM

So, after reading the results of the filtering ability of "high performance" panel filters vs. paper ones, I decided I'd retire the green cotton one as long engine life means more to me than 10hp at the top end. Local motor factors didn't have the OE Subaru part, so a very similar aftermarket equivalent was purchased, looked very much the same, folded red paper with squidgy black surround. First drive after fitting it I thought I detected a slight loss of power, but put it down to the weather and overtraining the previous night. Next morning it struggled a bit getting up the hill going out of the village, but I thought no more of it as it occasionally does anyway on cool damp mornings until the engine warms a bit. Then it started to struggle on a hill, middle of the day, warm engine - not good   :cray: , cue hooking up laptop and checking for fault codes: none. Following a hunch I dived into the Bay of fleas and quickly ordered up a genuine Subaru part, put it in yesterday and within 5 mins driving I have a happy Foz again  :yahoo:

May the Foz be with you....

#2 dnok

  • LocationElland West Yorkshire

Posted 23 May 2016 - 07:19 PM

Very interesting indeed.

So what was it that put you off the "performance filters"? Have they shown to let in a lot more crap to a point it actually becomes a problem?

#3 Blastertrev

  • LocationSunny Cumbria (NOT)

Posted 23 May 2016 - 11:47 PM

Well I'm not sure at which point it would become a problem - likely it will depend on exactly what kind of crap you're letting in, however I do sometimes have to drive down dusty farm tracks etc. (on the rare occasions it's not raining) so I'm going to take a slightly pessimistic view. But definitely "performance filters" do allow a lot more through - stands to reason really, to get more airflow, they have bigger holes; if I hold my green cotton one up to the light I can see tiny points of light shining through. Here's a couple of the tests I came across:


http://www.bobistheo...er/airtest1.htm - tested on a real car

http://www.nicoclub....oem-filter.html - tested according to a test standard


One thing that strikes me is that there's enough room in the air filter box in the Foz to fit a slightly thicker (top to bottom) filter, which should mean a bigger surface area = better airflow for a given dust retention rating.

May the Foz be with you....

#4 dnok

  • LocationElland West Yorkshire

Posted 24 May 2016 - 09:52 PM

Cheers for the links :)

#5 brownpantsracing

  • LocationBucks

Posted 02 June 2016 - 08:55 AM

I originally used a Do-Luck foam panel filter on my Impreza as it came top of the BHP back to back filter tests. However it's certainly worth having a look at them closely as it was so badly made I had concerns over how it was filtering and if it would last. I have used K&N ever since and they have always been great and given good results and peace of mind.

2004 FSTI, Modified 2006 Impreza, 1963 VW beetle. All on the road for once! Woo hoo! :)

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