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  #16  
Old 05-12-2007, 05:40 PM
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Quote:
Originally Posted by ItsPeteReally
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.
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  #17  
Old 05-12-2007, 06:19 PM
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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.
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1997 2.2ltr Subaru Impreza Outback Sport Wagon (AWD/Auto) 13.03@100mph
1989 2.7ltr Subaru XT6 (AWD/Auto) 15.912@85.93mph
1996 3.3ltr SVX (AWD/Auto) 15.070@91.38mph
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  #18  
Old 05-13-2007, 02:10 AM
ItsPeteReally ItsPeteReally is offline
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Quote:
Originally Posted by Trevor
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.
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.
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  #19  
Old 05-13-2007, 04:14 AM
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Quote:
Originally Posted by 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.
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.

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. The exercise requires expertise obviously beyond the ability of the author.
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  #20  
Old 05-13-2007, 06:48 AM
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Quote:
Originally Posted by 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.
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.
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  #21  
Old 05-14-2007, 07:09 AM
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Quote:
Originally Posted by ItsPeteReally
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.
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1997 2.2ltr Subaru Impreza Outback Sport Wagon (AWD/Auto) 13.03@100mph
1989 2.7ltr Subaru XT6 (AWD/Auto) 15.912@85.93mph
1996 3.3ltr SVX (AWD/Auto) 15.070@91.38mph
***R.I.P***
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  #22  
Old 05-14-2007, 07:19 AM
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Quote:
Originally Posted by Trevor
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.

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. The exercise requires expertise obviously beyond the ability of the author.
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?
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Kevin Thomas
1997 2.2ltr Subaru Impreza Outback Sport Wagon (AWD/Auto) 13.03@100mph
1989 2.7ltr Subaru XT6 (AWD/Auto) 15.912@85.93mph
1996 3.3ltr SVX (AWD/Auto) 15.070@91.38mph
***R.I.P***
2010 RAV4 AWD Sport (13.717 @ 99.19mph )
2015 Honda Fit LX CVT (15.2 @ 90mph)
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  #23  
Old 05-14-2007, 08:50 AM
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Quote:
Originally Posted by Myxalplyx
Chike....questions, comments, advice on this?
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.

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  #24  
Old 05-14-2007, 11:28 AM
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so... ummm... not worth it?
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  #25  
Old 05-14-2007, 04:57 PM
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Quote:
Originally Posted by Myxalplyx
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?
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  #26  
Old 05-15-2007, 04:43 AM
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Quote:
Originally Posted by Trevor
Yes, did I not make the probable errors clear?
Quote:
Originally Posted by Trevor
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. The exercise requires expertise obviously beyond the ability of the author.
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.

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!
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1997 2.2ltr Subaru Impreza Outback Sport Wagon (AWD/Auto) 13.03@100mph
1989 2.7ltr Subaru XT6 (AWD/Auto) 15.912@85.93mph
1996 3.3ltr SVX (AWD/Auto) 15.070@91.38mph
***R.I.P***
2010 RAV4 AWD Sport (13.717 @ 99.19mph )
2015 Honda Fit LX CVT (15.2 @ 90mph)

Last edited by Myxalplyx; 05-15-2007 at 04:45 AM.
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  #27  
Old 05-15-2007, 04:53 AM
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Quote:
Originally Posted by svxxx26
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.
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  #28  
Old 05-15-2007, 05:15 AM
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Quote:
Originally Posted by Trevor
Exactly Jerry.
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.
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1997 2.2ltr Subaru Impreza Outback Sport Wagon (AWD/Auto) 13.03@100mph
1989 2.7ltr Subaru XT6 (AWD/Auto) 15.912@85.93mph
1996 3.3ltr SVX (AWD/Auto) 15.070@91.38mph
***R.I.P***
2010 RAV4 AWD Sport (13.717 @ 99.19mph )
2015 Honda Fit LX CVT (15.2 @ 90mph)
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  #29  
Old 05-15-2007, 10:09 AM
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Quote:
Originally Posted by Myxalplyx
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.
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.
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  #30  
Old 05-15-2007, 05:56 PM
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Quote:
Originally Posted by Myxalplyx
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.
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.
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