jdblock

iTrader: (8)

It's time for me to replace the air filter in my stock intake. 2004 STi.

I don't want to use and oiled filter. Is the OEM filter the one to use, or is the filter from NAPA okay? I went and looked at the NAPA one today, and it doesn't look anything like the OEM, it has way too many pleats and I'm not sure it'll flow as well as the OEM.

Any other recommendation?

Heedz

iTrader: (51)

there's a few dry filters out there

AEM, AFE. I heard the cosworth one is like oem but flows really well.

I dunno personally it's nice to have the aftermarket so you can clean it. Oiled ones are bad if you OVER do it you know?

04GG

iTrader: (33)

Default recommendation: if you don't want oiled, stick with OEM.

I checked previously and there are no dry filters for our cars yet. I ran an oiled foam filter for a long time on my previous car with zero issues. I also have a Perrin filter that I ran on the WRX for almost a year, but I took swapped it back to OEM when I couldn't get a cleaning kit. I found a kit cheap, but still haven't put it back in.

The PCV is already venting some oil residue back into the intake as it is, so the oil from the filter is seriously not going to add anything more than what is already cycling through there IMO.

jdblock

iTrader: (8)

The issue with oiled filters isn't with the engine burning more oil, but rather the oil from the filter sticks to the MAF sensor and causes issues with fueling.

I've also seen a subjective test with the K&N filter on Bob Is The Oil Guy, the K&N was the worst filter out of the 5-6 the guy tested. This is one of the reasons I don't want an oiled filter and why I think I'm just going to stick with the OEM. For $11, it's just easier to throw in a new filter when needed, instead of cleaning one that cost 300-500% more.

Thanks for the response guys.

Cody8675309

iTrader: (3)

Yup, just buy OEM ones whenever Subaruparts.com or genuinsesubaruparts.com emails you that they are doing a free shipping + 10-15% off sale. You generally just have to spend $50 to get the sale deal though. If you don't get those emails, signup.

jdblock

iTrader: (8)

That's a good idea. Thanks.

Heedz

iTrader: (51)

But on the flip side. Sione here threw a cosworth one in and is boosting significantly faster. YFZ450LYNX pm him on how it made a huge difference.

04GG

iTrader: (33)

That's probably just because it is a K&N and does not have to do with the oil. For these cars, I've never heard a single recommendation for K&N. As Heedz mentioned, if you don't over oil the filter, clogging the MAF shouldn't be an issue either, but to be honest, there's nothing wrong with the OEM filter.

I actually dynoed a foam filter in my Type R. +2HP across the range. 4 runs - 2 foam, 2 stock, results the same both times, so it shows that it flows better, but isn't going to make a night and day difference IMO.

Hmmmm, hadn't seen that one before. I will have to research more. How would one clean it? Because that's pretty darn expensive if you have to toss it when it gets dirty.

*Edit - Rally Sport Direct said one time use, but it should last longer than the OE.

Cody8675309

iTrader: (3)

The conventional wisdom on the turbo Subarus that came with aluminum intake manifolds (before they changed the intake piping material and shape) is that the stock airbox won't be a bottlneck until around 300 or 350 WHP. Now I'm sure that a freer flowing filter media could help power, especially as you increase horsepower, but it's always going to be at the expense of filtration. If you live in an area with low dust, and every single HP matters to you, it might be worth it to you to get a reusable (oiled) filter.

And the MAF doesn't get "clogged" when you over-oil the filter media, it just gets oil on it and this makes the car run poorly. The solution is to clean the MAF with a can of MAF cleaner.

My tuner recommended that I stick with whatever filter I got tuned with since these cars are so finicky regarding intake changes. It's probably overly cautious, but if you're like me, you're overly cautious when it comes to maintenance.

04GG

iTrader: (33)

The foam filters typically increase filtration vs cotton (K&N) and paper, but they also get dirty faster because they retain that dust. I've read many times that MAF equipped cars should not use an oiled filter too.

It is basically clogging the MAF - the oil gets on it and dust sticks to the oil and disrupts air flow since we are talking about a very small port where the air flow is being read so it doesn't take that much to inhibit it - I had it happen on my S13 because the previous owner did not maintain it properly. I haven't actually looked at the MAF on this car, but I presume it is similar.

jdblock

iTrader: (8)

Here's the test of the 6 different filters. Yes its done on a Mazda Miata, but it shows some honest results. I don't think minimum amounts of gains are worth installing a filter that doesn't work as well as others, there's other ways of gaining power on turbo engines.

Air Filter Filtration Test - Bob is the Oil Guy

04GG

iTrader: (33)

That test didn't actually test real FLOW and he admits no measurements were taken. Those are assumptions based on particulation on the secondary filter that show the filtration capability, not flow. Note too that he also seems to be saying that the oiled filters showed no detectable oil on the secondary filter.

The stock intake on these cars is already pretty good and gains from a filter alone are probably not worth it until you start making quite a bit more than stock, at which point a different intake might be better. I like to try things for myself too though.

I've previously used a dual stage Jackson Racing filter on one of my Integras as well.

jdblock

iTrader: (8)

I agree. The gains from any filter other than stock wouldn't be worth the small gains (for me). I'd rather go CAI if I was looking for more power.

Heedz

iTrader: (51)

Now that's the wrong idea. CAI will do less.....

jdblock

iTrader: (8)

Fixed for me.

The CAI wouldn't be the only mod for power, a turbo would go on the engine with it. The VF39 (48?) I have on doesn't need much more air than what the stock box will handle.