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Old 04-24-2019, 10:44 AM   #1
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Side intake acting as venturi?

Maybe I'm looking at this incorrectly but wouldn't the side intake on the Boxster create a venturi effect and create a vacuum in the airbox?
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Old 04-24-2019, 12:10 PM   #2
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Maybe I'm looking at this incorrectly but wouldn't the side intake on the Boxster create a venturi effect and create a vacuum in the airbox?
No. Attach a digital manometer and take the car for a run, it is a slight positive pressure.
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Old 04-24-2019, 05:18 PM   #3
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No. Attach a digital manometer and take the car for a run, it is a slight positive pressure.
For sure it has to be, otherwise the engine wouldn’t be getting air at all. The question is, is the engine vacuum having to overcome a vacuum in the other direction?
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Old 04-24-2019, 05:46 PM   #4
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No, JFP just told you that there is a slight positive pressure. It's very unlikely that any manufacturer in modern times would release an air intake design that hurts performance.
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Old 04-24-2019, 06:42 PM   #5
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No, JFP just told you that there is a slight positive pressure. It's very unlikely that any manufacturer in modern times would release an air intake design that hurts performance.
um, I think what tgh was saying was that if the car was running and moving, the engine drawing air would create that pressure so not a true test. you could do it on the other side when the fan wasn't running to get a truer test.

if you look at velocity maps of cars you'll see that the air is at a lower velocity in that area relative to other areas of the car. perhaps due to turbulence induced by the front wheel? anyways, if the air moves slower relatively then there will be more of it in that area so higher pressure relative to the rest of the car.
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Old 04-24-2019, 07:30 PM   #6
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A set of these ram air ducts would be nice, but Kokeln went out of business and I have not been able to find them anywhere.

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Old 04-24-2019, 07:44 PM   #7
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.....if the air moves slower relatively then there will be more of it in that area so higher pressure relative to the rest of the car.
I had to read that twice..... and then think about it really hard, in order to wrap my mind around that. That's counter- intuitive.... but I think it's right..... right?

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Old 04-24-2019, 08:58 PM   #8
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I'm not sure what TRK was trying to say, either!

Ideally, an air intake is positioned at a high-pressure area, like the base of a windshield. The location of the engine in our cars rules that out, so Porsche has an intake on the side of the car, which isn't a high-pressure spot, Apparently, there is enough flow over the side intake that it isn't a problem.
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Old 04-24-2019, 10:01 PM   #9
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bernoulli effect - pressure is related to velocity. think a wing; the air traveling over the longer curved upper surface has to travel faster than the air following the shorter straight bottom surface if all air is to get to the back of the wing at the same time. the faster air gets 'spread out' (same unit of air has to cover larger area) and if volume increases then pressure has to decrease (pv=nrt). lower pressure on upper surface of wing means wing rises.

so, higher speed = lower pressure. conversely, lower speed = higher pressure. relatively (again, pv=nrt and if volume is proportional to velocity then a decrease in v means an increase in p). wind tunnel images show slower air in the area in front of the rear wheel.

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Old 04-25-2019, 02:34 AM   #10
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um, I think what tgh was saying was that if the car was running and moving, the engine drawing air would create that pressure so not a true test. you could do it on the other side when the fan wasn't running to get a truer test.

if you look at velocity maps of cars you'll see that the air is at a lower velocity in that area relative to other areas of the car. perhaps due to turbulence induced by the front wheel? anyways, if the air moves slower relatively then there will be more of it in that area so higher pressure relative to the rest of the car.
Exactly, if the engine is running it would be overcoming the vacuum. To properly test you’d have to test the fan side.
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Old 04-25-2019, 02:44 AM   #11
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[QUOTE=KRAM36;593723]A set of these ram air ducts would be nice, but Kokeln went out of business and I have not been able to find them anywhere.

demonspeed has the driver side intake for about $100.
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Old 06-04-2019, 12:04 PM   #12
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On my 2002 base. The shape of the air intake is different than the one on the passenger side(evacuation).

Look carefully at how the neck protrude at the fender surface. You will see that one goes out more than the other. In my opinion, this tuned by Porsche engineer ?
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Old 06-04-2019, 12:51 PM   #13
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In my opinion, this tuned by Porsche engineer ?
And? What's your point?
Is your suggestion that it shouldn't be messed with because it was designed by a Porsche engineer?
Let me ask then: do you think it was the same engineer who designed the IMS? or the 5-chain arrangement? Or the AOS system? Or the problematic and failure- prone oil-delivery? Or the window regulators? Or the cooling fan resistors? Or..... shall I go on?

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Old 06-04-2019, 03:39 PM   #14
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My point is the air intake or the heat exhaust vent have different shape exactly to prevent this venturi effect that the OP is talking about.

In my opinion, the AOS or the fan resistors and even the IMS are perfectly designed and all of those systems work for thousand and thousand miles like they are suppose to.

The fact that they fail on many cars, and I agree with you on this, is probably the consequence of suppliers who put crap in the material used to build the parts.

But again, this is just my non engineer opinion.
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Old 06-04-2019, 03:46 PM   #15
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On my 2002 base. The shape of the air intake is different than the one on the passenger side(evacuation).

Look carefully at how the neck protrude at the fender surface. You will see that one goes out more than the other. In my opinion, this tuned by Porsche engineer ?
On my 03 Boxster S, the passenger side (USA) vent pulls air into the engine compartment.
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Old 06-04-2019, 05:33 PM   #16
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Maybe I'm looking at this incorrectly but wouldn't the side intake on the Boxster create a venturi effect and create a vacuum in the airbox?
Visually, looking down the side of the car, you can see that the intake vent presents a certain amount of its cross section (although at an angle) into the airstream flowing around the car. It looks like it catches air so it is not likely that a negative pressure or suction could be created a the air box entry.
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Old 06-04-2019, 06:23 PM   #17
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My point is the air intake or the heat exhaust vent have different shape exactly to prevent this venturi effect that the OP is talking about.
Agreed!

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Old 06-06-2019, 11:01 PM   #18
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On my 03 Boxster S, the passenger side (USA) vent pulls air into the engine compartment.
Exactly right. I don’t understand how the fallacy persists that the right side vent intake is an exhaust but I see it a lot.

If you want to prove it for yourself, when stopped place a strip of tissue paper over the vent when the engine compartment fan is running. Just be sure not to let it be sucked in.

It is true that heat radiates from the vent when stopped if the fan is not running but that is true for the entire mid/rear section of the car including the wheel wells.
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Old 06-07-2019, 08:31 PM   #19
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Exactly right. I don’t understand how the fallacy persists that the right side vent intake is an exhaust but I see it a lot.

If you want to prove it for yourself, when stopped place a strip of tissue paper over the vent when the engine compartment fan is running. Just be sure not to let it be sucked in.

It is true that heat radiates from the vent when stopped if the fan is not running but that is true for the entire mid/rear section of the car including the wheel wells.
I don't know why people keep saying this either? If people want proof, I'll hook up my Durametric and have it turn on the fan for that vent and video record a piece of paper being sucked to the vent.
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