Air Filter Housing Restriction

[Topless]

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.

[Jaxonalden]

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.

[Boxtaboy]

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.

[Padawan]

Originally Posted by Jaxonalden

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.

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

[coreseller]

Originally Posted by Padawan

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.

[Jaxonalden]

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.

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!

[Quickurt]

Originally Posted by Jaxonalden

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.

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?

[Jaxonalden]

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

[ekam]

Originally Posted by Topless

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.

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

[Jaxonalden]

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.

[Boxtaboy]

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

[jmatta]

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.

[Jaxonalden]

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.

[jmatta]

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.

[Adam]

Originally Posted by Jaxonalden

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.

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

[Jaxonalden]

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

[blue2000s]

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.



2) Here's the sheet at the end.



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



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



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



6) Pressure drop with the 1.85" tube



7) Pressure drop with the 3" tube



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%.

[Jaxonalden]

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. Beers on me if we ever meet.