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Old 03-30-2015, 02:18 PM   #1
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Riddle me this - Engineers / Eng Students

Everyone likes to put a cold air intake on these cars, correct?

Well, look right over the top of your stock air box. What is right there on the hood? One of the heat extractors, correct?





Now, stay with me here....

What direction does air go through that heat extractor? Out, correct? At speed, that's a low pressure area and draws air OUT.

It won't show on the dyno, but I'm almost willing to bet that at speed, with these open air intakes that seal up against the hood, you're actually seeing a pressure drop at the filter if your intake seals against that vent.

Minute? Maybe.

Theorectically correct? I would think so, as that heat extractor works on the Venturi effect.
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Old 03-30-2015, 02:21 PM   #2
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Riddle me this - Engineers / Eng Students

Now say everything you just wrote in dumb English for any of those who didn't keep up. Lol
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Old 03-30-2015, 02:35 PM   #3
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I'm still a fresh engineering student, but that makes sense to me. Another reason to stick to the factory intake system.
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Old 03-30-2015, 02:53 PM   #4
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Okay, that heat extractor on the hood doesn't face INTO on coming air does it. It faces away. That means the open side, the back, isn't under positive pressure it's under vacuum. As air goes over that vent, the pressure is higher UNDER the hood than it is OVER the hood....meaning air wants to come OUT that vent. That's a venturi effect, using the pressure differential to direct air flow.

Now, if you use one if these intake that has a seal that goes up against the hood and air is trying to go IN front the inlet in the grill and OUT at that heat extractor, that would cause a pressure drop for anything within that air box.

You won't see it on the dyno as usually the hood is open and evennif the hood is closed, fans won't generate enough speed to cause that effect. But, in real conditions, there is a slight vacuum on that heat extractor.
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Old 03-30-2015, 03:08 PM   #5
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Very simple example of this....

Drive along and stick your hand out the window and put it just over your mirror. You feel the air pressure, right?

Now, move it down behind the mirror. Now you're in a turbulent area that is in drag and a lower pressure. The faster air is trying to pull things OUT of that area.

You know when you wash your car and as you drive it the water left inside the mirror gets pulled out and ticks ya off because you just washed and waxed it? Same effect.
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Old 03-30-2015, 03:25 PM   #6
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Essentially, with an open-element CAI, that vent would be stealing air that is intended for your engine.
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Old 03-30-2015, 03:59 PM   #7
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Correct. But, this would only apply to the ones that are open on top and use a rubber gasket to essentially seal against the hood. The closed-type airboxes that only draw air in from the opening at the grill don't have this effect.


Now, like I said, it's likely a miniscule amount, but an amount none the less. Instead of seeing 101 kPa of barometric pressure, you may be seeing, as an example, 98 kPa at 30 MPH, 95 kPA at 60 MPH, etc. You'd need to put a pressure sensor in there to see the actual difference, but the difference would increase as speed increases.


Easy way to address it.....just put some duct tape on the back side of that heat extractor if it's actually in the area of your open air box.


I don't know why this popped into my head, I was just walking out to the car and when I was looking as I walked up a light bulb came on.
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Old 03-30-2015, 05:13 PM   #8
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Definitely a valid argument, I'm glad you took the time to post it. Non-engineer-likeminded people could use the clarification.
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Old 03-30-2015, 05:29 PM   #9
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I may try a little experiment if I get a few minutes. It won't be anything sophisticated but it'll prove the principle.....

I'll see if I have anything that will generate some smoke and I'll put it near the grill. I'll just use a leaf blower and direct it so the air flows over that heat extractor. If it draws the smoke through, it shows it has merit.

Hmmmm.......
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Old 03-31-2015, 11:36 AM   #10
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Glad I went with Airaid!
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Old 03-31-2015, 12:12 PM   #11
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That is a heat extractor period. there is no vacuum at that point, the nose of your car is providing positive pressure to the engine bay. I seriously doubt the there is a venturi effect because of the position and design. There is probably a boost effect at high speeds but very little at best. Again those vents are to relieve pressure inside the engine bay and thereby pull out some of the hot air generated by the radiator.
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Old 03-31-2015, 02:22 PM   #12
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Correct. The problem is that vent is off to the side. With the stock air box it has flow to it, but the air boxes that seal against the underside of the hook isolate that vent. The inlet to airbox doesn't get any boost effect with way it's oriented behind the grill. The grill is actually closed off in front of that air inlet to the box. If you look at the grill on the car, you'll see what I mean.
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Old 03-31-2015, 02:42 PM   #13
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Here's what I'm talking about. The actual open area of the grill pretty much corresponds with the shrouded portion of the radiator....





The air inlet is behind the closed portion of the grill...



The opening to that vent is directly over where my finger is pointing....



I know it's tough to see from the picture, but there is no opening in front of the airbox that actually gets flow from the grill area. Nearly everything is directed to the radiator and shrouding in the center...



Like I was saying, probably miniscule at best and you'd never see it on the dyno, but I'd be willing to bet there is an effect there.
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Old 03-31-2015, 03:56 PM   #14
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Well it makes sense to me, however I also think that a small negative pressure at that point would allow more air to come in through grill mounted inlet duct. Which would mean more cooler air.
The question is then, what is the net result of available air to the filter? Perhaps still a miniscule amount but of perhaps cooler air?
What you may have to look at is the final impact to inlet air to the engine. As in temperature and A/F ratio.
Let us know what you find out.
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Old 03-31-2015, 04:00 PM   #15
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Quote:
Originally Posted by SilverS550 View Post
I may try a little experiment if I get a few minutes. It won't be anything sophisticated but it'll prove the principle.....

I'll see if I have anything that will generate some smoke and I'll put it near the grill. I'll just use a leaf blower and direct it so the air flows over that heat extractor. If it draws the smoke through, it shows it has merit.

Hmmmm.......
With the engine running of course! (That is another variable!)
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Old 04-01-2015, 06:59 PM   #16
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Glad I went with Airaid!
This may be the exact reason Airaid went with a sealed style intake
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Old 04-01-2015, 07:13 PM   #17
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If you sealed your intake to that, you would technically be creating a low pressure condition for your intake boot.

Unless you are driving in reverse.

They literally make intakes that seal to that extractor? Its meant to coax air OUT of the engine bay.. wtff. Their entire customer base failed physics in high school. There is no other explanation lol

The stock air filter layout is right. That extractor will work well to promote airflow to the filter when its in that position, and not let hot air be trapped under the hood.

I feel like, if you sealed the intake boot to that, then the car would just choke out and die if you went over 150mph lol. Maybe its a safety feature!

or it could be good for fuel economy, you see, when the engine isn't getting any air into it, then it also wont use much fuel!! GENIUS!!!!
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Old 04-01-2015, 07:33 PM   #18
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Quote:
Originally Posted by Panther140 View Post
If you sealed your intake to that, you would technically be creating a low pressure condition for your intake boot.

Unless you are driving in reverse.

They literally make intakes that seal to that extractor? Its meant to coax air OUT of the engine bay.. wtff. Their entire customer base failed physics in high school. There is no other explanation lol

The stock air filter layout is right. That extractor will work well to promote airflow to the filter when its in that position, and not let hot air be trapped under the hood.

I feel like, if you sealed the intake boot to that, then the car would just choke out and die if you went over 150mph lol. Maybe its a safety feature!

or it could be good for fuel economy, you see, when the engine isn't getting any air into it, then it also wont use much fuel!! GENIUS!!!!
Sealed as in, OEM style sealed box that pulls cold air from the duct in the grill. Not sealed to the heat extractor.
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Old 04-01-2015, 07:45 PM   #19
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That is the dumbest sh*t on the market and I don't see how people are falling for that. It's essentially Ford's "box" design with the Airaid logo on it. The resusable filter is not an excuse as you can just buy a resusable drop-in filter.

Waste of $300.
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Old 04-01-2015, 07:50 PM   #20
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I'm just saying that at least they took into account the placement of the heat extractor lol

Sent from the Death Star.
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Old 04-02-2015, 05:58 AM   #21
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The Airaide solution is not just pulling air in via the OEM grill slot through their washable filter. It's what Airaid does to the air flow AFTER the filter.

Or I wasted $300,
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Old 04-02-2015, 06:53 AM   #22
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Quote:
Originally Posted by scurfie View Post
The Airaide solution is not just pulling air in via the OEM grill slot through their washable filter. It's what Airaid does to the air flow AFTER the filter.

Or I wasted $300,
I am not familiar with airraids design. They have an intake coming from the shroud in front of the car.. is that right? Because thats logical.

They also have a tube that seals up against the evacuation vent on the hood, correct? Because that would be somewhat logical as long as there is also another port of entry into the airbox.

That would indeed increase the air velocity in some situations. At this point, its a question of how well the inside of their airbox takes advantage of that increased air velocity.

If they did it right, then the throttle response would benefit from it while the vehicle is moving. There will always be fresh air in there, and the air will never be stagnant. Plus, im sure the intake sounds cooler with that port being exposed to the outside of the car

Am I gonna buy one though? no. I can get a nitrous kit for $100 more than the cost of one of those. That air is much colder.
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Old 04-02-2015, 09:12 AM   #23
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Am I gonna buy one though? no. I can get a nitrous kit for $100 more than the cost of one of those. That air is much colder.
I like how you think
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Old 04-02-2015, 02:51 PM   #24
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They also have a tube that seals up against the evacuation vent on the hood, correct?
No
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Old 04-02-2015, 03:20 PM   #25
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I'm gonna go ahead and say the vacuum created by the engine would overpower any slight pressure change that makes the heat extractor work. I've seen engines implode partially blocked filters( industrial engines I work on). I see it as another cold air inlet under WOT. If the air box seals around the hole in the hood it's going to offer another air inlet. But we are talking about a perfect seal now. Id be more worried about water getting on an open filter.
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Old 04-02-2015, 04:31 PM   #26
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Ideally, what you want from a CAI is to slightly pressurize the box at speed. You want to lower the restriction from the filter, but ideally it should pressurize the box slightly at speed. It you have an opening in the front it'll achieve that. But, the opening to that inlet is behind the grill so you get no "ram air" effect. By having that heat extractor located where it is, even if the box was otherwise sealed to the hood, and I mean a perfect seal, that heat extractor would negate any "ram" effect you might get.


Like I said....miniscule, but not ideal. With a closed filter setup, no impact at all. With an open filter, it certainly wouldn't allow it any ram effect from the high pressure in front of the car.
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Old 04-02-2015, 05:47 PM   #27
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Quote:
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The Airaide solution is not just pulling air in via the OEM grill slot through their washable filter. It's what Airaid does to the air flow AFTER the filter.

Or I wasted $300,
If you don't mind, would you please elaborate what Airaid's design does to the airflow after the filter?
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Old 04-02-2015, 06:11 PM   #28
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If you don't mind, would you please elaborate what Airaid's design does to the airflow after the filter?
https://www.airaid.com/intakesystems.aspx
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Old 04-02-2015, 06:17 PM   #29
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Dude i hate to say it, but im not a belieber about these things at $300. unless you got some track times or even just dyno numbers that would make me change my mind. I would look at it as possible a touch more hp, but better induction sound, and it looks trick.
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Old 04-02-2015, 07:22 PM   #30
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If you want to see if your stock intake is actually a restriction it's not that hard. You know those little filter minders that are in every single chevy intake? Just fit one to the port where the sound tube is. That'll tell you if there is vacuum being created between the filter and throttle body.
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Old 04-03-2015, 01:13 PM   #31
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So they changed the name from cold air box to cold are dam.

I was hoping for a logical answer, but still only see a marketing ploy.

Think about it. How long has Ford been around? Is the small difference between stock tube and the Airaid tube warrant a $350 price tag?
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Old 04-03-2015, 01:35 PM   #32
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As with any engineered component, there are 3 forces acting on it...

1 - The requirements to make it fit (engineers)
2 - The requirement to make it perform (engineers)
3 - The requirement for it to be profitable (bean counters)

Engineering doesn't always win.

If you want to measure the difference between the 2 tubes, start by measuring the inside diameter of that convoluted section of the stock tube vs the inside of the airaid tube. That small convoluted section will induce turbulence right before the throttle body, even if it's the same minor diameter as the TB itself.

Doesn't matter how long Ford has been in business....if no expense was spared in the production of power, we'd all be driving half million dollar super cars, but instead we're driving $30k Mustangs.
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Old 04-03-2015, 05:54 PM   #33
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You have a point. What I don't have is the desire to be the test dummy who goes out and buys one to compare them side-by-side.
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