Air Filter Housing Restriction
 

I recently bought a stock air filter assembly with a K&N filter off of EBay to to see what I could do to modify it. I immediately noticed that just prior to the MAS, the housing has a built in, very fine, screen. I can just imagine the restriction this imposes, just as bad if not worst than the snorkel. I'm going to see what the best way to remove this is, then remove the one on my car and give it a "seat of the pants" check. Any suggestions?



http://986forum.com/forums/attachmen...tid=9739&stc=1

http://986forum.com/forums/attachmen...tid=9740&stc=1

IS it sandwiched in between two sections that can be taken apart and reassembled without the screen?
If not, it looks like a very careful die grinder job. Don't try a hole saw, as it will grab the screen and probably tear up the whole thing.
You will have to cut through one wire at a time, far enough away from the throttle body to not damage it, then carefully grind each wire to flush with the inner bore.
Looks like a PITA, but I'd say your right about the restriction, it's hideous!
One question: is it doing something to the airflow so that the MAS works properly?

While watchin' the season premier of "The Office" I started messing around and found a couple of locking tabs. With a screwdriver I was able to pop the locks, squeeze my hand into the air filter hole and pull the "snorkel like" end with the screen attached!! This can be done with the filter housing on the car.

Yes Virginia, there is another free upgrade you can do to you car.

http://986forum.com/forums/attachmen...tid=9741&stc=1

http://986forum.com/forums/attachmen...tid=9742&stc=1

http://986forum.com/forums/attachmen...tid=9743&stc=1

With this piece removed, the screen can be removed more easily and the velocity stack can be reinstalled.

http://986forum.com/forums/attachmen...tid=9744&stc=1

I also took a picture of the snorkel that's removed through the left intake vent, just in case anyone was wondering what it looks like.

http://986forum.com/forums/attachmen...tid=9746&stc=1

Just remember Porsche didn't put that screen in there just to piss you off. It is there to prevent your motor from injesting large chunks that often fall into the bottom of the air box when changing the filter. Toolpants has some great pictures of nasty STUFF in the air box. Big bugs, ciggy butts, chunks-o-rubber etc.

As long as you clean around the filter box before you pull the filter tray out, you should be fine. If "Big bugs, ciggy butts, chunks-o-rubber etc." are getting past the air filter, what the hell is the air filter even there for? Sorry, but if ******************** like that is on the filtered side someone must be running with NO filter.

I know of no other company that has a screen to catch the big chunks. I'm cutting out this screen and replacing the one in my car.

Wow, there sure are a lot of restrictions in the airbox. Thanks for sharing.

I'll probably keep mine in because with my luck, when I remove my air filter to replace it, some crap will fall into that area before I even get a chance to stick my vacuum down the airbox. :D

Hey now. It's just this week's episode on "How I out smart Porsche engineers". :)

Boxtaboy,

I understand your concerns, but don't stop with the P car. As I said in my post, I don't know of any other car that has a screen aft of the air filter. So if you own other cars you should be just as careful not to leave any screws, paperclips or club sandwiches in your air box. :)

Ekam,

I'm not trying to outsmart the Porsche engineers, I'm just trying to free up the car from the federal mandates that are imposed on imports. You know the ones that limit performance in the name of the environment and keeping the neighbors happy. :cheers:

True, I doubt it would be a big deal either way. Let us know if you feel or hear any difference.

I certainly don't have those problems since I yanked out my stock air box and replaced it with an EVO Hi-Flow three years ago. Forget the fairytales of CEL and MAF problems; if you know how to properly oil a cone filter, those problems don't arise. You'll never get the sound an EVO produces with a modified stock box.

Jmatta,

I'm with ya on the properly serviced, cottom based, oil filter thing. Some people just soak the media to the point of it dripping. Just follow the directions!

I'd love to put an EVO on my car. But cost and the love of tinkering prohibit it at this time. I'll let the forum know after I swap out for the screenless stack.

I hear you...good luck on the swap. I truly believe Porsche purposely put all this stuff in our cars (baffles, screens, secondary cats) to keep them quiet for the EU restrictions. Our cars should have a nice sound, just as Dr. Porsche intended them to in the beginning.

Most of them do. In fact, every car I've worked on that had a MAF (as opposed to a MAP) had a screen like the one here.

Not only does it serve to keep out "large chunks", but it more importantly influences airflow over the sensor.

You can read more here: http://www.gmtips.com/3rd-degree/dox/tips/maf/maf-screen.htm

Ditto that. I've put in a couple of CAI (Cold Air Induction) kits in other cars, I haven't encountered one without the screen, domestic or import. Oh and BTW, there was always a seat of the pants difference felt with them, one verified a 13 HP increase on the dyno, these completely replaced the stock airboxes though.

OK, I'll post this to anyone out there that has an EVO intake installed. Does that intake have a screen just before the OEM Mass Airflow Sensor? I went to the site that sells them and could not see or read that it does. It does utilize the stock sensor so, if you guys are right, will have this screen installed. I checked my SUV, my wife's car and my Harley and none of then have a screen in front of the MAS. Everything else I own has a carburetor.

I can see where you think it should. In high RPM engines, the air flowing past the MAS will act like a wing on a high performance aircraft and will create a boundary layer of air giving false readings. The screen will act as vortex generator breaking up that boundary layer. On an aircraft wing it allows the flight controls to be more effective at high air speeds.

So with that said I need someone that knows first hand what the EVO intake has inside that pipe. Pictures would be nice also. Until then I'm swapping out for my screen-less stack (which only took an Exacto knife to cut out). If I get a CEL, I will post it and won't hide the fact that I was wrong in my assumption. :cheers:

I should just go ahead an get the EVO because the air in a stock air box takes no less than 4-90 degree turns in less than 12 inches!

You may not get a Change Engine Light, but it may run like crap or stumble at certain RPM ranges, etc.
I put a K&N ram tube, ot whatever they called it, on an RX8 and it used the original MAS and had no screen in it, but neither did the OEM airbox.
Made the car so loud on intake noise, I couldn't stand it.
Know anyone who wants one?

Swap out and 50 mile test drive complete. No CEL and I can swear that the intake noise is throatier, maybe the screen suppresses some noise. Driving the car through the twisty's does seem to run similar to a sexual molested primate. IMHO :cheers:

While sitting around this weekend I decided to do a little research on a couple of issues;

1. Over servicing of K&N air filters. That myth is settled here;
http://www.knfilters.com/MAF/massairfindings.htm

2. Removal of the intake screen (reason for the thread). I've visited sites, read posts and learned about the different mass air flow sensors. We utilize the hot wire type. The wire is maintained at a constant temp and the air flow moving across it will cause it to loose heat faster. The ECU will compensate by sending more current and measures this current flow and puts out a voltage signal. This wire is made of platinum (hence the $250+ replacement cost) and is susceptible to damage if a foreign object should come in contact with it, (the screen). So are the internals of our engines, so if this happens I think the MAF is the last thing I would worry about.

The wire is self cleaning, (from what I read) at engine shut down this wire is heated to 1800 degrees to clean itself, unlike a dog that can lick his balls. :rolleyes: A couple GM forums had CFM numbers with and W/O the screens but the 180CFM difference was based on their size and density of screen. I know ours is restrictive and the filter I use will keep out anything harmful. As I've said, I will continue to run without. If a CEL occurs and its determined to from the MAF I'll post the results.

Hi, Thanks and keep us posted and I like your :rolleyes:

:cheers:

Except that the Boxster doesn't use a Hot-wire sensor... it uses a Hot-film sensor similar to mylar, it is conductive and so can be heated. It is not however self-cleaning - at 1800 degrees, the film would simply melt.

Those screens have no discernible effect on the airflow through the intake. Removing it may make you feel like you've done a free mod, but really, it had no effect on the engine that you will ever notice. Send it to me and I'll put it on my flow bench to prove it to you.

This type of screen also is not used as any kind of a "flow conditioner" for feeding into the MAF. Screens that serve that purpose need to have "depth" in the direction of flow like a honeycomb-type screen.

My only guess is that this screen was added to prevent large particles from being ingested by the intake. I agree, that it's impossible for something to make it that far into the intake if the rest of the system is intact, but there must have been some significant "what if?" scenario that Porsche saw fit to protect from.

Send me a PM and I'll send you my address. You can put it in an envelope and I'll bench test it.

Will do, but first...I have my stack with the screen removed in now. You want to use the stack with the screen? Or do you just want the screen I removed so you can just wrap it around a tube that you already have base-lined?

LB,

I just compared the pictures of the OEM and the one in the article I read. Seemed the same one to me...I use the E-Gas model...especially after eating Mexican food. :rolleyes:

For those interested, I'm sending Blue2000s my cutout screen in the morning and we should have flow bench results in about a week. I was just thinking, Blue2000S, if you use a clear tube can you light a cigarette or something that smokes and report on the looks of the airflow aft of the screen?

Thanks for taking this on for the forum.

FYI, here's the description of the MAF from the DME Motronic 7.2 (E-Gas) Diagnostics manual:

"Mass Air Flow Sensor

The mass air flow sensor is installed between the air cleaner and the throttle valve, and measures the mass air flow taken in by the engine. An electrically heated platinum resistance film is cooled by the air flow. A control circuit corrects
the heating current in such a way that the temperature of the resistance film rises constantly in relation to the intake air temperature. The heating current is then a means of measuring the mass air flow. With this method of measurement, the air density is also taken into consideration, as it helps to determine the amount of heat emitted from the heated body into the air. A temperature sensor is integrated for measuring the intake air temperature."

Update on the Flowbench Check
 

Blue2000S has my old screen and will conduct the flow bench check through the screen next week he said. In the mean time, I've got a flow meter that I use to balance my sand rails twin 44 IDF's. I was thinking that I could put my snorkel back on and place the flow meter on the snorkel and measure the flow rate at idle. Then install the intake screen and read the meter again. There should be a delta, and that delta would be the restriction, at idle. :cheers:

Here's a MAF sensor for a corvette. Actually I think screens are pretty common for MAF sensors.

OK, I stand corrected. By the looks of that screen I can't see any restriction :rolleyes: . As for me, I'm running without it.

Thanks to Jaxonalden for sending the screen. I had a little time to put it on the flow bench today.

Here's an explanation of the test:
1 - A tube is sealed to the front of the flow bench
2 - A very accurately measured amount of air is drawn through the tube
3 - The screen is then placed on the end of the tube and the air is drawn through again
4 - The difference in pressure drop between the test with the screen and without will give you the pressure drop for the screen for any given volume flow rate.

There is some dependancy in this test on the diameter of the tube, and I couldn't use a 3" tube that would be near the intake diameter of the Boxster because I wouldn't have been able to hold onto it, so my tube diameter is smaller, 1.85". What this means is that the pressure drop for a given CFM will be about 1/4 for the 3" tube of what it is for the 1.85" tube that I'm using. I've got a plot for the 1.85" tube and a corrected plot for the 3" tube.

Here are some pictures:

1) Here's the tube ready for the flow bench. It is attached to the bench with the cardboard sheet at the center. The sheet at the end is used to attach the screen.

http://i2.photobucket.com/albums/y37...reen/tube1.jpg

2) Here's the sheet at the end.

http://i2.photobucket.com/albums/y37...reen/tube2.jpg

3) This is the tube attached to the flow bench.

http://i2.photobucket.com/albums/y37...reen/tube3.jpg

4) This is the end sheet with the screen attached.

http://i2.photobucket.com/albums/y37...reen/tube4.jpg

5) The pressure curve of the tube with and without the screen

http://i2.photobucket.com/albums/y37.../tube_flow.jpg

6) Pressure drop with the 1.85" tube

http://i2.photobucket.com/albums/y37...screenflow.jpg

7) Pressure drop with the 3" tube

http://i2.photobucket.com/albums/y37...nflow3inch.jpg

A 3.2L engine at 7200 RPM is moving about 400CFM at 100% volumetric efficiency. It's probably more like 50% at redline. So you can see at 200CFM, the pressure drop is 0.2 inches of water, or about 0.0072 psi. Which for the uninitiated is very small. The % increase in pressure between with and without the screen is about 5-6%.

Blue2000S,

Thanks so much for doing the leg work for the members of the Forum. I didn't realize there was so much to getting the real numbers. Like I said, I thought you could just put a flow meter on and read the delta. This is obviously the correct way to do it. If I understand your last statement, the difference is 5-6% or about 24 CFM increase over the 400 CFM @ 7200 rpm.

Power increase if any? My guess is the engine would enjoy the better breathing. Again, thanks to Blue2000S for the great work. :cheers: Beers on me if we ever meet.

So those fellows at Porsche and Bosch must be idiots if they put a restrictive screen in the works. I just don't get it.

The pressure drop is negligable. If I tested the drop due to the MAF itself, it would be considerably more. Even an elbow in the intake will be significantly higher drop. This type of screen is usedin every MAF based car I've looked at so Porsche's not doing anything different than anyone else and they're not significantly effecting airflow with it.

Just because I question the restriction and need of the screen doesn't mean I'm smarter than the OEM. I'd just like to know why its there and is it needed? If everything the OEM does is correct, we should never have to touch our cars, right?

None of us do anything to our cars because they're perfect. Just gas and go. F-that, I'm going to tweak with the engine freeing up, what I think, the Government suppresses in the name of the EPA. Free flow exhaust, mapping, air cleaner, brake upgrade...oh wait, those Porsche fellows must be idiots.