Air Filter Housing Restriction - Page 2 - 986 Forum - The Community for Porsche Boxster & Cayman Owners

blue2000s · 09-28-2008, 03:06 PM

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.

Jaxonalden · 09-28-2008, 04:00 PM

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.

Jaxonalden · 09-28-2008, 06:55 PM

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.

Lil bastard · 09-28-2008, 09:27 PM

Quote:

Originally Posted by Jaxonalden

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.

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."

Jaxonalden · 10-04-2008, 09:55 AM

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.

Adam · 10-04-2008, 10:30 AM

Quote:

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 · 10-04-2008, 10:49 AM

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 · 10-06-2008, 01:59 PM

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 · 10-06-2008, 06:54 PM

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.

wvicary · 10-07-2008, 04:12 PM

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.

blue2000s · 10-07-2008, 05:01 PM

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.

Jaxonalden · 10-07-2008, 10:08 PM

Quote:

Originally Posted by wvicary

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.

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.