STi air filter.

[AlcyoneDaze]

well, its that time again; my air filter is starting to get cruddy and I think I recall seeing somewhere here that you can replace the SVX filter with an STI drop in filter, which flows a little better and frees up some trapped horsies. So... I just walk in the Subie dealer and ask for an STi air filter element? is it worth the extra price? what model year should I be trying to get, etc?

[Myxalplyx]

well, its that time again; my air filter is starting to get cruddy and I think I recall seeing somewhere here that you can replace the SVX filter with an STI drop in filter, which flows a little better and frees up some trapped horsies. So... I just walk in the Subie dealer and ask for an STi air filter element? is it worth the extra price? what model year should I be trying to get, etc?

Chike....questions, comments, advice on this? :confused: :D

[2NI]

A lot of Subaru airboxes have the same design and that way share the same filter element. All Euro turbo Impreza's for exemple (GC8 & GDB) have the same airbox as our SVX's. So, that brings us here: if you cannot find a specific filter for the SVX, just ask for a WRX model. ;)
I (like in a lot of my previous cars for ex. Impreza, M3, & current V40 turbo) put a "Green Filter" in the airbox. Why Green & not K&N for exemple? Well, it's cheaper & has a supposed better airflow.

Also because it's easy to find around here like it's manufactured locally (France).

Voilà!

[Gizmotronicus]

A lot of Subaru airboxes have the same design and that way share the same filter element. All Euro turbo Impreza's for exemple (GC8 & GDB) have the same airbox as our SVX's. So, that brings us here: if you cannot find a specific filter for the SVX, just ask for a WRX model. ;)
I (like in a lot of my previous cars for ex. Impreza, M3, & current V40 turbo) put a "Green Filter" in the airbox. Why Green & not K&N for exemple? Well, it's cheaper & has a supposed better airflow.

Also because it's easy to find around here like it's manufactured locally (France).

Voilà!

Plus oiled filters such as K&N will clog your maf over time.

[Myxalplyx]

Plus oiled filters such as K&N will clog your maf over time.

What do you mean by 'clogging' your maf over time? How long does it take before it clogs your maf? All my Subarus (with the exception of the SVX) have K&N air filters. No 'clogging'! My outback has used a K&N air filter going on 9 years now.

[SVXRide]

I think the reference is to those that don't read the directions when cleaning/oiling their K&N filters...

The "GREEN" filter is also a good option.

-Bill

[ensteele]

If the filter is oiled to heavy, it may contaminate the MAF and get it dirty so it will not function properly. :)

[Trevor]

The name of the after market game and typically K&N. There are no wild horses out there awaiting a corral. The Subaru engineers have them all rounded up. :rolleyes: :D

[svxxx26]

I've wasted money on the K&N filters, et. al.

Placebo effect is a great description. I used mine until it got dirty, then replaced it with a paper Purolator filter. Same exact performance noted in the seat of my pants, so I think the "performance" filters are useless, at least in a stock engine.

[Myxalplyx]

The name of the after market game and typically K&N. There are no wild horses out there awaiting a corral. The Subaru engineers have them all rounded up. :rolleyes: :D

So, there is no horsepower to be gained by changing the air filter to an STi air filter you are saying?

[b3lha]

An ordinary paper filter, when new and clean, flows as much air as the engine needs. A "performance" filter that allows more air to flow provides no benefit because the engine will still take the same amount of air.

If you replace a dirty clogged up paper filter with a shiny new "performance" filter then of course you will see a benefit. But you would see the same benefit with a shiny new paper filter for a lot less money.

I ran one of my previous cars with no filter at all for a while. Better flow than any "performance" filter, but it made no difference at all to the performance.

My father inlaw lives in Africa where dust is a big problem. His fiat has an oiled filter and a ordinary paper filter in series. I guess the oiled filter helps to stop the paper one getting clogged up so quickly.

[ItsPeteReally]

An ordinary paper filter, when new and clean, flows as much air as the engine needs.

Thats true at anything less than full throttle. Most of the time the driver limits the air flowing into the engine by applying less than full throttle and any other limitation of the airflow into the engine goes unnoticed.

But there is always a pressure drop across the air filter which increases as the engine revs rise and the engine tries to consume more air. If all other effects are discounted, removing the filter will increase the airflow into the cylinders when the throttle is wide open.

But there are other effects, which makes the outcome much more difficult to predict: the most obvious one being a change in the resonant behaviour of the inlet tract, caused by the change in the effective length and the amount of resonant damping.

My best guess is that the resonant frequency of the inlet tract drops and becomes 'peakier' ...... but the only way to be sure is to actually measure the flow

[ensteele]

For the kind of driving I do, paper filters will do just fine then. :) :)

[Darren]

Hiya,

I have an STI panel filter fitted, probably not worth the retail cost, the only benefit is the engine revs a little quicker in the midrange but nothing like the "add 20bhp" filter adverts claim for after market filters.

If you dont mind spending the cash there is a small performance benefit from the STI filter, bare in mind it was developed for the impreza in Group N rallying where they had to use a standard airbox, the flip side they may not be designed to last as long as a standard paper filter, time will tell, as at today mine has done around 4000 miles and is like new.

Darren

[Landshark]

for the price, the disposable STi filter is not worth it.

i have a Perrin foam panel filter, and like it alot (especially because it was free.) it is reusable, but unlike the crappy K&N, it filters better, and the thick oil it uses will not foul the MAF.

[Trevor]

Thats true at anything less than full throttle. Most of the time the driver limits the air flowing into the engine by applying less than full throttle and any other limitation of the airflow into the engine goes unnoticed.

But there is always a pressure drop across the air filter which increases as the engine revs rise and the engine tries to consume more air. If all other effects are discounted, removing the filter will increase the airflow into the cylinders when the throttle is wide open.

But there are other effects, which makes the outcome much more difficult to predict: the most obvious one being a change in the resonant behaviour of the inlet tract, caused by the change in the effective length and the amount of resonant damping.

My best guess is that the resonant frequency of the inlet tract drops and becomes 'peakier' ...... but the only way to be sure is to actually measure the flow

The after market, the word “market” is significant, relies on the fact that specific measurements are very difficult to establish and assumptions become the basis of argument.

Manufactures most certainly take into account full throttle performance. Media testing has a profound affect on sales. When assessing the issue the layman should observe and give thought to the relative area of the OEM filter enclosure, as compared to the area of the inlet tract.

Rather that guess in regard to the pros and cons, I can put forward practical evidence. I have some experience with production car road circuit racing, whereby the regulations required that the OEM or an exactly fitting filter of alternative manufacture, be used. I became aware that several competitors were cheating by modifying there filter elements.

As a result I carried out a simple test to establish if they were placing me at a disadvantage. During practice, I removed the filter from my car, (On this occasion a Subaru FF1). The result was no improvement in lap times, which had been established as absolute maximum performance. As a result I refrained from protesting against the opposition, leaving them in dreamland. :rolleyes: :D

[Myxalplyx]

Check this link out-->
http://www.autospeed.com/cms/article.html?&A=0629

It is an Autospeed article titled, "Eliminating Negative Boost". Perhaps a manometer like the one that is used in the article can be used to measure the effectiveness of replacing the stock air filter with an STi one.

[ItsPeteReally]

Rather that guess in regard to the pros and cons, I can put forward practical evidence. I have some experience with production car road circuit racing, whereby the regulations required that the OEM or an exactly fitting filter of alternative manufacture, be used. I became aware that several competitors were cheating by modifying there filter elements.

As a result I carried out a simple test to establish if they were placing me at a disadvantage. During practice, I removed the filter from my car, (On this occasion a Subaru FF1). The result was no improvement in lap times, which had been established as absolute maximum performance. As a result I refrained from protesting against the opposition, leaving them in dreamland. :rolleyes: :D
A not too unsurprising result.

For anybody who wants to remove a lot of guesswork and have, or are building, a data gathering ECU interface that can record MAF voltage and engine rpm, they can actually perform an experiment to settle the matter.

Choose any air filter(s) you want, or no air filter at all, and plot the airflow against engine rpm at full throttle.

The inlet setup that has the greatest area under the MAF voltage curve wins. I'd be surprised if there were no differences at all. Whether the differences are significant or not is a different matter.

[Trevor]

Check this link out-->
http://www.autospeed.com/cms/article.html?&A=0629

It is an Autospeed article titled, "Eliminating Negative Boost". Perhaps a manometer like the one that is used in the article can be used to measure the effectiveness of replacing the stock air filter with an STi one.

The article is written in a style befitting the anticipated readership, is typical of many magazines. The prospect of accurately measuring, a pulsating airflow moving at speed, through a tube at relatively low pressure, via small protruding orifice, mounted at right angles to the flow is mind boggling. :rolleyes:

Briefly consider the principal of an atomizer, wave shape of the airflow, variations across the conducting cross section and the affect of RPM, all in relation to the figures published. :rolleyes: The exercise requires expertise obviously beyond the ability of the author. :p

[svxxx26]

Check this link out-->
http://www.autospeed.com/cms/article.html?&A=0629

It is an Autospeed article titled, "Eliminating Negative Boost". Perhaps a manometer like the one that is used in the article can be used to measure the effectiveness of replacing the stock air filter with an STi one.

Here's a little tip for the author of that article: When writing about technical subjects, write like your audience is older than 12 years old. He may have had some points in there somewhere but I never got to them.

[Myxalplyx]

For anybody who wants to remove a lot of guesswork and have, or are building, a data gathering ECU interface that can record MAF voltage and engine rpm, they can actually perform an experiment to settle the matter.

Choose any air filter(s) you want, or no air filter at all, and plot the airflow against engine rpm at full throttle.


There is a simple piece of software for this type of measurement. It is called a 'Pocketlogger'. http://www.pocketlogger.com/?pid=obdii
I have one and have used it in the past. I have never figured out how to put the graphs onto my computer to upload the data that I recorded. If someone else here has this or a similar product, perhaps they can post up the data. It is a nifty piece of software. Good at looking at ECU codes and removing them too.

[Myxalplyx]

The article is written in a style befitting the anticipated readership, is typical of many magazines. The prospect of accurately measuring, a pulsating airflow moving at speed, through a tube at relatively low pressure, via small protruding orifice, mounted at right angles to the flow is mind boggling. :rolleyes:

Briefly consider the principal of an atomizer, wave shape of the airflow, variations across the conducting cross section and the affect of RPM, all in relation to the figures published. :rolleyes: The exercise requires expertise obviously beyond the ability of the author. :p

Did you say all of this to say that the device used in the article can not be used to show the difference between an STi air filter and a stock one?

[Chiketkd]

Chike....questions, comments, advice on this? :confused: :D
Sorry I didn't see this thread sooner. I never had any problems with the STI air filter I used in my former SVX (now Myxalplyx's car) and I bought one for my current WRX as well. They're kinda pricey ($70) and I doubt they outflow other high performance air filters on the market (K&N, Perrin, Green, etc) but it is a performance item made by Subaru FWIW. If you want something cheaper that'll probably flow just as well, look at the other options others have mentioned in this thread.

http://www.subaru-svx.net/photos/files/Chiketkd/22963.jpg

[AlcyoneDaze]

so... ummm... not worth it?:D

[Trevor]

Did you say all of this to say that the device used in the article can not be used to show the difference between an STi air filter and a stock one?

Yes, did I not make the probable errors clear? :confused:

[Myxalplyx]

Yes, did I not make the probable errors clear? :confused:

Briefly consider the principal of an atomizer, wave shape of the airflow, variations across the conducting cross section and the affect of RPM, all in relation to the figures published. :rolleyes: The exercise requires expertise obviously beyond the ability of the author. :p

I do not deal with atomizer principals, wave shapes of airflows, variations across conducting cross sections, etc. I am not an expert any any of those fields as I am sure most people aren't. The article was simple and done for many people to understand. Measuring airflow does not have to be rocket science. :p

Sorry, I do not mean to take this thread out of context. Just wanted to show a means to measure the difference in effectiveness of airflow between the stock air filter and the STi air filter. That's all! :)

[Trevor]

Here's a little tip for the author of that article: When writing about technical subjects, write like your audience is older than 12 years old. He may have had some points in there somewhere but I never got to them.

Exactly Jerry. :confused: :D

[Myxalplyx]

Exactly Jerry. :confused: :D

Let me help you out with just one quote from the article-->

"Hmm, so how much loss is there through the filter? Very nearly nothing at all! And guess what? That is the case on nearly every car - the standard filter poses very little restriction at all in the system. Look at the Before Filter and After Filter lines - don't get much closer than that, do ya? In the Audi's case, the filter makes up 1 inch of water pressure drop out of the 32 inches total pressure drop that is present. In other words, 97 per cent of the flow restriction of the intake is not the filter. And to hammer home the point, when you make actual on-car measurements, it's pretty well always like this. The airfilter as a halitosis-suffering, smelly, dirty, hairy negative pressure is a total frame-up created by those with vested interests in selling drop-in aftermarket replacement filters."

Although it supported what you spoke of earlier, somehow you failed to understand that. :confused: :rolleyes:

[svxxx26]

Let me help you out with just one quote from the article-->

"Hmm, so how much loss is there through the filter? Very nearly nothing at all! And guess what? That is the case on nearly every car - the standard filter poses very little restriction at all in the system. Look at the Before Filter and After Filter lines - don't get much closer than that, do ya? In the Audi's case, the filter makes up 1 inch of water pressure drop out of the 32 inches total pressure drop that is present. In other words, 97 per cent of the flow restriction of the intake is not the filter. And to hammer home the point, when you make actual on-car measurements, it's pretty well always like this. The airfilter as a halitosis-suffering, smelly, dirty, hairy negative pressure is a total frame-up created by those with vested interests in selling drop-in aftermarket replacement filters."

Although it supported what you spoke of earlier, somehow you failed to understand that. :confused: :rolleyes:

Kevin - glad to hear there was some relevant info in the article, I just got tired of wading through the drive-thru burnout references and other ridiculousness of the author's writing style. Not sure what his target audience was, but I wasn't in it. It's like, will you please just get to the point?
I edit a lot of articles in real life so maybe it's just me. ;)

[Trevor]

Let me help you out with just one quote from the article-->

"Hmm, so how much loss is there through the filter? Very nearly nothing at all! And guess what? That is the case on nearly every car - the standard filter poses very little restriction at all in the system. Look at the Before Filter and After Filter lines - don't get much closer than that, do ya? In the Audi's case, the filter makes up 1 inch of water pressure drop out of the 32 inches total pressure drop that is present. In other words, 97 per cent of the flow restriction of the intake is not the filter. And to hammer home the point, when you make actual on-car measurements, it's pretty well always like this. The airfilter as a halitosis-suffering, smelly, dirty, hairy negative pressure is a total frame-up created by those with vested interests in selling drop-in aftermarket replacement filters."

Although it supported what you spoke of earlier, somehow you failed to understand that. :confused: :rolleyes:

Kevin,

The weight behind the statement made, directly depends on the evidence which has been presented. Therefore the statement carries no weight and is worthless in this context, however true it may be. :)

[Myxalplyx]

Kevin,

The weight behind the statement made, directly depends on the evidence which has been presented. Therefore the statement carries no weight and is worthless in this context, however true it may be. :)


Ohh...I like this statement a lot. May make it a quote in my signature. It may come back to haunt you Trev. Beware!!! :eek: :D

[Trevor]

Ohh...I like this statement a lot. May make it a quote in my signature. It may come back to haunt you Trev. Beware!!! :eek: :D

:confused: You may do with it as you will (provided it remains complete), but before you do so, please read again and understand the words "in this context." :rolleyes: :)