Air Filter Housing Restriction

[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.

[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.

[blue2000s]

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]

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.