Aftermarket air filters
Discussion
I am considering fitting an aftermarket air filter to a 993.
I was only looking at replacement elements for the airbox, not cones or Gruppe M systems.
I understand performance gains are negligible,but you may as well have evertything on your side.
The options seem to be between K&N or BMC. I have used K&N before on other cars, does anyone have any experience of BMC? or any preference between the two?
I was only looking at replacement elements for the airbox, not cones or Gruppe M systems.
I understand performance gains are negligible,but you may as well have evertything on your side.
The options seem to be between K&N or BMC. I have used K&N before on other cars, does anyone have any experience of BMC? or any preference between the two?
Hi Clubsport, I fitted a K&N filter and the Porsche Sound Enhancement Package (drilled airbox cover) last summer.
Definatly made a difference, induction noise is greater and the car seems much more responsive, (it seems more eager)I understand that this option was not allowed in Germany, so it must do something naughty!
I got both from Type 911 for £74 and £54 respectively.
You dont get much for £128 these days and considering that the airbox cover is OE, I think that it represents good value.
I do not think that you get much in BHP terms, and as my 993 has lots of other minor improvements its difficult to guage.
Try it, its only money!
Definatly made a difference, induction noise is greater and the car seems much more responsive, (it seems more eager)I understand that this option was not allowed in Germany, so it must do something naughty!
I got both from Type 911 for £74 and £54 respectively.
You dont get much for £128 these days and considering that the airbox cover is OE, I think that it represents good value.
I do not think that you get much in BHP terms, and as my 993 has lots of other minor improvements its difficult to guage.
Try it, its only money!
Cheers David, I have the drilled airox which makes more than enough induction noise...I think our Noble friend Joust has a recoeding to that effect.
Happy to spend the dough, but want to get the right on.I heard that the oil on a K&N can mess with the MAF sensor on a 996, not sure if this applies to a 993 though?
Happy to spend the dough, but want to get the right on.I heard that the oil on a K&N can mess with the MAF sensor on a 996, not sure if this applies to a 993 though?
I don't want to burst anyone's bubble or step on any toes, but the K&N orgainzation has a much better marketing department than they do research and development.
They could sell you a glass of salt water standing on the sea side.
K&N filters are "notorious" for oiling down MAF and hotwire sensors and causing all kinds of problems. They are also known for admitting high levels of silica, the stuff that comes off the highway when it's worn down by traffic. People who run fleet trucks, and who do oil analysis, have good data with the K&N products, and the readings give "high silicon content" with K&N filters because they let more unfiltered material get into the motor.
Anyone who thinks they're going to get more performance out of a Porsche by drilling an air box is fooling themselves, has a bit too much time on their hands, and is just wanting to work on the car. Hey, I want to work on my car too, but I'm not going to defeat the engineering department in Zuffenhausen with a hand drill and a K&N air filter.
Porsche is not like economy car manufacturers, who might have skimped on the air box and filter. Porsche is fanatical about engineering, and they're not going to put an ineffective filter or a too small air box on an engineering masterpiece.
For instance, and we'll just use round numbers as an example: say you have an air box with a 7 x 12" filter medium. That would be just about 84 square inches of high flowing K&N filter medium, and because the K&N has a little wave in the surface, let's just be nice and say it's 100 square inches.
The stock filter on a 944 for instance, is one inch tall, and has 10 double sided pleats per inch. Therefore it has 7" of width just like the K&N, but it also has 20" of filter medium per inch of length due to the 10 double sided pleats (in a filter which is 12" long). Therefore one inch of stock filter length has more surface area than the entire K&N filter.
Final tally: K&N 100 square inches of filter area, stock "Premium Plus" Purolator A23191 (replaces AF3191)
has around 1680 square inches of filter medium.
The stock Purolator won't flow as well as a K&N "inch for inch" of surface area, but it doesn't need to. It has so much more surface area, it can afford to pass a smaller amount of air per square inch, filter much better, and still provide more air than the weakest link in the intake system can handle, which is normally the throttle body opening.
I purchased a K&N for my 1984 944 and got one for my 1983 928 BEFORE I heard all about this from an expert in the field. I verified it, and guys, I'll send you a photograph of me holding a lighter under one of those oiled up sponge pieces of junk. If they make the car sound better, well hmmmm, I'd just as soon take a long neck chisle to the interior of my muffler and pull out some stainless steel wool.
Any thought that the K&N is going to make your car go faster is pure fiction. Numerous dyno tests will show it is not going to happen on a Porsche. Perhaps a Toyota, but not on a car engineered at the onset for performance.
Hey, may I now have a ladder so I can get down from this soapbox and tiptoe quietly to the corner? :-)
Dogsharks
They could sell you a glass of salt water standing on the sea side.
K&N filters are "notorious" for oiling down MAF and hotwire sensors and causing all kinds of problems. They are also known for admitting high levels of silica, the stuff that comes off the highway when it's worn down by traffic. People who run fleet trucks, and who do oil analysis, have good data with the K&N products, and the readings give "high silicon content" with K&N filters because they let more unfiltered material get into the motor.
Anyone who thinks they're going to get more performance out of a Porsche by drilling an air box is fooling themselves, has a bit too much time on their hands, and is just wanting to work on the car. Hey, I want to work on my car too, but I'm not going to defeat the engineering department in Zuffenhausen with a hand drill and a K&N air filter.
Porsche is not like economy car manufacturers, who might have skimped on the air box and filter. Porsche is fanatical about engineering, and they're not going to put an ineffective filter or a too small air box on an engineering masterpiece.
For instance, and we'll just use round numbers as an example: say you have an air box with a 7 x 12" filter medium. That would be just about 84 square inches of high flowing K&N filter medium, and because the K&N has a little wave in the surface, let's just be nice and say it's 100 square inches.
The stock filter on a 944 for instance, is one inch tall, and has 10 double sided pleats per inch. Therefore it has 7" of width just like the K&N, but it also has 20" of filter medium per inch of length due to the 10 double sided pleats (in a filter which is 12" long). Therefore one inch of stock filter length has more surface area than the entire K&N filter.
Final tally: K&N 100 square inches of filter area, stock "Premium Plus" Purolator A23191 (replaces AF3191)
has around 1680 square inches of filter medium.
The stock Purolator won't flow as well as a K&N "inch for inch" of surface area, but it doesn't need to. It has so much more surface area, it can afford to pass a smaller amount of air per square inch, filter much better, and still provide more air than the weakest link in the intake system can handle, which is normally the throttle body opening.
I purchased a K&N for my 1984 944 and got one for my 1983 928 BEFORE I heard all about this from an expert in the field. I verified it, and guys, I'll send you a photograph of me holding a lighter under one of those oiled up sponge pieces of junk. If they make the car sound better, well hmmmm, I'd just as soon take a long neck chisle to the interior of my muffler and pull out some stainless steel wool.
Any thought that the K&N is going to make your car go faster is pure fiction. Numerous dyno tests will show it is not going to happen on a Porsche. Perhaps a Toyota, but not on a car engineered at the onset for performance.
Hey, may I now have a ladder so I can get down from this soapbox and tiptoe quietly to the corner? :-)
Dogsharks
Clubsport has summed it all up in one line. IF you are correct Dogsharks, then why do Porsche themselves fit K&N clone BMC filters onto the GT3 Cup cars??
Secondly, if everyone were to adopt the ridiculous attitude that "Porsche knows best" there would be no place for tuner/developers like myself improving engine outputs from 78 to 103 bhp per litre now, would there?
There are some very valid points in your arguments, but as a K&N user/engineer/retailer I can confirm that we have dyno tested induction kits and replacement panel filters and in many cases gained power (although some are better than others for sure).
Secondly, if everyone were to adopt the ridiculous attitude that "Porsche knows best" there would be no place for tuner/developers like myself improving engine outputs from 78 to 103 bhp per litre now, would there?
There are some very valid points in your arguments, but as a K&N user/engineer/retailer I can confirm that we have dyno tested induction kits and replacement panel filters and in many cases gained power (although some are better than others for sure).
dogsharks said:
I don't want to burst anyone's bubble or step on any toes, but the K&N orgainzation has a much better marketing department than they do research and development.
They could sell you a glass of salt water standing on the sea side.
K&N filters are "notorious" for oiling down MAF and hotwire sensors and causing all kinds of problems. They are also known for admitting high levels of silica, the stuff that comes off the highway when it's worn down by traffic. People who run fleet trucks, and who do oil analysis, have good data with the K&N products, and the readings give "high silicon content" with K&N filters because they let more unfiltered material get into the motor.
Anyone who thinks they're going to get more performance out of a Porsche by drilling an air box is fooling themselves, has a bit too much time on their hands, and is just wanting to work on the car. Hey, I want to work on my car too, but I'm not going to defeat the engineering department in Zuffenhausen with a hand drill and a K&N air filter.
Porsche is not like economy car manufacturers, who might have skimped on the air box and filter. Porsche is fanatical about engineering, and they're not going to put an ineffective filter or a too small air box on an engineering masterpiece.
For instance, and we'll just use round numbers as an example: say you have an air box with a 7 x 12" filter medium. That would be just about 84 square inches of high flowing K&N filter medium, and because the K&N has a little wave in the surface, let's just be nice and say it's 100 square inches.
The stock filter on a 944 for instance, is one inch tall, and has 10 double sided pleats per inch. Therefore it has 7" of width just like the K&N, but it also has 20" of filter medium per inch of length due to the 10 double sided pleats (in a filter which is 12" long). Therefore one inch of stock filter length has more surface area than the entire K&N filter.
Final tally: K&N 100 square inches of filter area, stock "Premium Plus" Purolator A23191 (replaces AF3191)
has around 1680 square inches of filter medium.
The stock Purolator won't flow as well as a K&N "inch for inch" of surface area, but it doesn't need to. It has so much more surface area, it can afford to pass a smaller amount of air per square inch, filter much better, and still provide more air than the weakest link in the intake system can handle, which is normally the throttle body opening.
I purchased a K&N for my 1984 944 and got one for my 1983 928 BEFORE I heard all about this from an expert in the field. I verified it, and guys, I'll send you a photograph of me holding a lighter under one of those oiled up sponge pieces of junk. If they make the car sound better, well hmmmm, I'd just as soon take a long neck chisle to the interior of my muffler and pull out some stainless steel wool.
Any thought that the K&N is going to make your car go faster is pure fiction. Numerous dyno tests will show it is not going to happen on a Porsche. Perhaps a Toyota, but not on a car engineered at the onset for performance.
Hey, may I now have a ladder so I can get down from this soapbox and tiptoe quietly to the corner? :-)
Dogsharks
Interestingly, my local engine tuner that does work for GM and helped develop the Noble engine mods has tried all these filters including K&N and they made no difference at all. In some cases they made matters worse. Fuel injection systems are so efficient and compensating that any 'improved flow' (improved flow, less filtration!) filters have no effect.
Interestingly, in the days when I was less wise, I used K&N and wondered why a standard paper filter is v dirty after say 10K wheras, when you wash the K&N hardly any dirt at all!!
Neinmeister, read this carefully. I'm trying to share information with you, and the guy who asked the initial question, not argue. You said....
"Clubsport has summed it all up in one line. IF you are correct Dogsharks, then why do Porsche themselves fit K&N clone BMC filters onto the GT3 Cup cars??"
Here is the answer to your question. "Because those cars are putting out horsepower waaay above stock (meaning, they are pumping a lot more air), they are modified in "every way", and filtration is secondary to them because those engines are torn down for other reasons, on schedule or by necessity".
(see link I added to bottom of this post, 600-hp 944. Now thats an application that exceeds the stock engineering, and yes, a different filter is appropriate there).
We are discussing what is appropriate for a STOCK application. The stock motor pumps a known amount of air. The weak link in a stock motor is the throttle body. With no filter at all, the weak link (point of maximum constricted air flow)is still the throttle body. Putting a fancy foam "racing air filter" won't change a thing, because the stock air filter has so much surface area, it is not a power robber. The size or the air box and filter was engineered by Porsche, not the K&N marketing department, lol.
If you change the throttle body, increase compression, put in a hot cam, add more fuel with larger injectors, add turbocharging, and generally tweak the living heck out of the motor then the stock filter will be challenged and will need to be upgraded to meet the higher air flow requirements of the motor.
A stock 944 engine will not benefit from a K&N filter. I contend it will be harmed by one, because instead of good paper filter media, you have transparent foam that relies on oil to catch a chance piece of dirt. After a few miles, the dirt can become dislodged and still get to the engine. Once a K&N oil is no longer at optimum "test condition" they pass a lot of dirt. The paper filter just keeps on filtering. I don't like the thought of driving on public roads and sucking in dirt into an expensive piece of machinery, especially when I'm paying high dollars for good synthetic oil to keep it in good condition.
A 944 engine is capable of 600-hp in racing form (see link). Any cup racer or super high performance application like this will be pumping a lot more air than a stock 944. Therefore, the stock air box and filter is no longer appropriate, because it was "engineered by Porsche" for the stock application. THAT IS WHY you see K&N (or similar clones) on race cars. Be advised, those race cars are "totally" redone, almost every component is upgraded, and in order to produce higher power, they must pump more air. They go to a custom filter situation that does not care about small amounts of dirt, because all they are interested in is the win.
Since I assume you are not driving around in a highly modified car, I'm also assuming you won't need the "race-car-filter" on your ride, either.
Again, I'm sharing info, not arguing nor flaming here. However, the comment posted about people entrusting "Porsche knows best" makes me chuckle. Who would you trust, the boys in Zuffenhausen, or the aftermarket filter manufacturing sales and marketing department? With all of the fanatical attention given to drivability, power, performance times, and international press scrutiny, I doubt if Porsche has the idiot mentality to install a filter that some boy-racer can replace with foam and go faster :-)
Bottom line: On highly modified competition motors that are running well beyond the stock application then use an aftermarket filter for higher air flow. On stock applications where the stock air filter is far far from being a restriction, there is absolutely nothing to be gained by using an aftermarket filter, because you probably won't notice "any" difference on the dyno even if you run with no filter, because the filter is sized properly and is NOT the restriction the various marketing departments claim it is.
Hey, your car, your money, your choice.
(photo of me lighting a match to my K&N will follow)
See this link for a 600-hp 944. This is an application where the stock filter is not designed to meet the flow requirement of the engine. Notice the engine photos, and the custom "HUGE" race-only intake plenum and runners. This FAR exceeds a stock motor air flow. The filter they use is just about as good as stretching panty hose over the intake, just to keep large objects out. For a stock motor, save your money guys! Putting a "race car filter" on your car isn't going to make it a race car, nor will you be a race car driver. You'll just be a lighter in the wallet.
www.lindseyracing.com/cust1a.htm
cheers and regards,
Dogsharks
>> Edited by dogsharks on Monday 24th November 17:06
"Clubsport has summed it all up in one line. IF you are correct Dogsharks, then why do Porsche themselves fit K&N clone BMC filters onto the GT3 Cup cars??"
Here is the answer to your question. "Because those cars are putting out horsepower waaay above stock (meaning, they are pumping a lot more air), they are modified in "every way", and filtration is secondary to them because those engines are torn down for other reasons, on schedule or by necessity".
(see link I added to bottom of this post, 600-hp 944. Now thats an application that exceeds the stock engineering, and yes, a different filter is appropriate there).
We are discussing what is appropriate for a STOCK application. The stock motor pumps a known amount of air. The weak link in a stock motor is the throttle body. With no filter at all, the weak link (point of maximum constricted air flow)is still the throttle body. Putting a fancy foam "racing air filter" won't change a thing, because the stock air filter has so much surface area, it is not a power robber. The size or the air box and filter was engineered by Porsche, not the K&N marketing department, lol.
If you change the throttle body, increase compression, put in a hot cam, add more fuel with larger injectors, add turbocharging, and generally tweak the living heck out of the motor then the stock filter will be challenged and will need to be upgraded to meet the higher air flow requirements of the motor.
A stock 944 engine will not benefit from a K&N filter. I contend it will be harmed by one, because instead of good paper filter media, you have transparent foam that relies on oil to catch a chance piece of dirt. After a few miles, the dirt can become dislodged and still get to the engine. Once a K&N oil is no longer at optimum "test condition" they pass a lot of dirt. The paper filter just keeps on filtering. I don't like the thought of driving on public roads and sucking in dirt into an expensive piece of machinery, especially when I'm paying high dollars for good synthetic oil to keep it in good condition.
A 944 engine is capable of 600-hp in racing form (see link). Any cup racer or super high performance application like this will be pumping a lot more air than a stock 944. Therefore, the stock air box and filter is no longer appropriate, because it was "engineered by Porsche" for the stock application. THAT IS WHY you see K&N (or similar clones) on race cars. Be advised, those race cars are "totally" redone, almost every component is upgraded, and in order to produce higher power, they must pump more air. They go to a custom filter situation that does not care about small amounts of dirt, because all they are interested in is the win.
Since I assume you are not driving around in a highly modified car, I'm also assuming you won't need the "race-car-filter" on your ride, either.
Again, I'm sharing info, not arguing nor flaming here. However, the comment posted about people entrusting "Porsche knows best" makes me chuckle. Who would you trust, the boys in Zuffenhausen, or the aftermarket filter manufacturing sales and marketing department? With all of the fanatical attention given to drivability, power, performance times, and international press scrutiny, I doubt if Porsche has the idiot mentality to install a filter that some boy-racer can replace with foam and go faster :-)
Bottom line: On highly modified competition motors that are running well beyond the stock application then use an aftermarket filter for higher air flow. On stock applications where the stock air filter is far far from being a restriction, there is absolutely nothing to be gained by using an aftermarket filter, because you probably won't notice "any" difference on the dyno even if you run with no filter, because the filter is sized properly and is NOT the restriction the various marketing departments claim it is.
Hey, your car, your money, your choice.
(photo of me lighting a match to my K&N will follow)
See this link for a 600-hp 944. This is an application where the stock filter is not designed to meet the flow requirement of the engine. Notice the engine photos, and the custom "HUGE" race-only intake plenum and runners. This FAR exceeds a stock motor air flow. The filter they use is just about as good as stretching panty hose over the intake, just to keep large objects out. For a stock motor, save your money guys! Putting a "race car filter" on your car isn't going to make it a race car, nor will you be a race car driver. You'll just be a lighter in the wallet.
www.lindseyracing.com/cust1a.htm
cheers and regards,
Dogsharks
>> Edited by dogsharks on Monday 24th November 17:06
Generalising about engine tuning is fraught with problems, each case must be analysed on its own merit and judged accordingly. For example:
A standard 964 throttle body flows enough air for 325bhp: it is therefore not a restriction in the system.
A standard 930 turbo throttle body flows enough air for 460bhp at 1.0 bar boost. so it is also not a restriction.
A standard 3.2 Carrera throttle body flows enough air for 275bhp, so neither is this a restriction.
On all the above engines and more besides we have seen significant power gains from the mere substitutng a new paper element with a K&N style panel or cone filter; furthermore the results are from engines we have tuned and tested ourselves.
I have no doubt that an incorrectly oiled filter will deposit some of its oil into the airstream which could contaminate a hot film air flow meter, although I have not experienced this particular problem myself. We often replace hot films on standard Boxsters and 996s though, so the paper element is not exactly trouble free either if we are to accept the conclusion that faults in these parts are caused by filtration.
I have experienced problems first hand with over-oiled K&N type filters, had the problem with my own 993RSR that would not idle correctly due to a saturated cone element (not a K&N but similar) which disappeared when the K&N panel filter and airbox were replaced.
I suspect that paper elements are fitted for expense/environmental waste issues by manufacturers as well as their filtration properties, but to date all racing applications that I have ever seen or worked on used non-paper elements, so this kind of confirms the paper as a non-performance option.
Anyway, you will never negate a warranty if you keep a standard filter in a standard airbox on a standard engine with a standard DME, so anyone who is unsure should obviously adopt this approach and sleep well at night.
A standard 964 throttle body flows enough air for 325bhp: it is therefore not a restriction in the system.
A standard 930 turbo throttle body flows enough air for 460bhp at 1.0 bar boost. so it is also not a restriction.
A standard 3.2 Carrera throttle body flows enough air for 275bhp, so neither is this a restriction.
On all the above engines and more besides we have seen significant power gains from the mere substitutng a new paper element with a K&N style panel or cone filter; furthermore the results are from engines we have tuned and tested ourselves.
I have no doubt that an incorrectly oiled filter will deposit some of its oil into the airstream which could contaminate a hot film air flow meter, although I have not experienced this particular problem myself. We often replace hot films on standard Boxsters and 996s though, so the paper element is not exactly trouble free either if we are to accept the conclusion that faults in these parts are caused by filtration.
I have experienced problems first hand with over-oiled K&N type filters, had the problem with my own 993RSR that would not idle correctly due to a saturated cone element (not a K&N but similar) which disappeared when the K&N panel filter and airbox were replaced.
I suspect that paper elements are fitted for expense/environmental waste issues by manufacturers as well as their filtration properties, but to date all racing applications that I have ever seen or worked on used non-paper elements, so this kind of confirms the paper as a non-performance option.
Anyway, you will never negate a warranty if you keep a standard filter in a standard airbox on a standard engine with a standard DME, so anyone who is unsure should obviously adopt this approach and sleep well at night.
well the company I am associated with does extensive dyno work for their own development projects and others.
In many cases of highly tuned engines one does away with the hot wire/film and uses throttle angle instead to feed the ECU. This is because if one uses wilder cams they often send back pulses of air throught the hot wire system and upset it.
There has not been one case where a K&N filter has added gains- not one!!
There has been a whole industry founded on marketing hype but of course if people feel happier firring them they shold do so!
In many cases of highly tuned engines one does away with the hot wire/film and uses throttle angle instead to feed the ECU. This is because if one uses wilder cams they often send back pulses of air throught the hot wire system and upset it.
There has not been one case where a K&N filter has added gains- not one!!
There has been a whole industry founded on marketing hype but of course if people feel happier firring them they shold do so!
clubsport said:
HHHmmm!!! The £8 for a replacement standard paper filter is starting to look like a hassle free option.
Many thanks for the responses guys, this thread has been more enlightening than i ever hoped for.
I'm with you. Paul. IMO I would stick with the Porsche filter.
Oh, I had my car on the rolling road last night. It should have produced 250 bhp. It produced 262 bhp at the flywheel, 224 at the rear wheels. I think its been chipped somewhere...
If your 944 is a turbo it may just have been because it was a cold day. Or maybe the rollers were a little out of calibration. The only sure way to tell is to download the chip data (I have done this on a car before and had it analysed - I was sure it was chipped but the only variable was a later ECU code change to something like the time the glovebox stays on 
)
) 
domster said:
Bollox to filters anyway. I'm going to fit six trumpets and put some chicken wire over the top of them.
That must be worth a couple of bhp at the rear wheels and 20 bhp at the pub chatting to Iguana
Good man!
Btw, you say "at the pub chatting to Iguana" but surely you mean "standing around a disused oil drum warming up us hands?"
(P.S. Just dropped orf Splurter for his new clutch treatment; the boy H was showing me some fascinating print outs from a recent 550 mod which meant the best part of
all to moi but I'm sure it was damnably impressive.) 'Dorff.
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