Side intake acting as venturi?

[truegearhead]

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?

[JFP in PA]

Originally Posted by truegearhead

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.

[truegearhead]

Originally Posted by JFP in PA

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?

[Racer Boy]

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.

[The Radium King]

Originally Posted by Racer Boy

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.

[KRAM36]

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.

[maytag]

Originally Posted by The Radium King

.....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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[Racer Boy]

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.

[The Radium King]

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.

[truegearhead]

Originally Posted by The Radium King

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.

[Lemming]

[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.

[pomerlo]

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 ?

[maytag]

Originally Posted by pomerlo

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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[pomerlo]

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.

[KRAM36]

Originally Posted by pomerlo

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.

[jaykay]

Originally Posted by truegearhead

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.

[maytag]

Originally Posted by pomerlo

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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[Oldcarguy]

Originally Posted by KRAM36

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.

[KRAM36]

Originally Posted by Oldcarguy

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.