Air circulation in the 'stock' engine bay.

[Falundir]

I've always hated that the mailslot was non functional, so this new toy interests me (http://www.camaro5.com/forums/showthread.php?t=230368), however I am concerned that introducing a way to get more air into the engine bay without extracting the additional hot air might add a complication.

Does anyone have any knowledge on this?

[BubbaSS]

I don't think it would be enough air to make much difference, just nice to have it functional.

[The Stig]

Yes, forcing air into the engine bay without having any means of letting the air escape will cause problems. Imagine that your pumping air into a pressurized tank, normally these tanks have a blow off valve so that the excess pressure can escape. Without heat extractors you're running without a blow off valve. If you continue to pump air into the tank, it will eventually explode.


EDIT: as the above poster mentioned, it *may* not be enough air to matter. But the same principle applies.

[Falundir]

ACS' theory is that it would force out the bottom. I'd kill to see some circulation maps. Don't we have GM engineers on here we could bug? =)

[PAUL SS]

Originally Posted by stieger

Yes, forcing air into the engine bay without having any means of letting the air escape will cause problems. Imagine that your pumping air into a pressurized tank, normally these tanks have a blow off valve so that the excess pressure can escape. Without heat extractors you're running without a blow off valve. If you continue to pump air into the tank, it will eventually explode.


EDIT: as the above poster mentioned, it *may* not be enough air to matter. But the same principle applies.

However the engine compartment is not a sealed vessel that can maintain any kind of pressure, there is lots ways for air to escape. I do think hood vents would be a good idea as heat rises and they would provide an easy, natural exit for the heat. I too like the idea of making the mailslot somewhat functional.

[Synner]

Any lift from that minimal of airflow would likely be negligible unless you have plans to run the texas mile in which case you should be considering aero for high speed stability increases. Don't over think it, get it if you want it although hood vents would move a lot more air and likely improve aero.

[matt55]

Isn't that more of a low pressure zone where the mail slot is?
So it could let hot air out? And not "ram" it in.
Any aero geeks on here?

[Intimidator]

I have taken the rubber seal off from around the wiper area under the hood, this seems to allow some of the heat to escape....since this is my daily driver and I drive it alot in the rain and wash it once a week, you would think water would be all over the engine bay without the seal...but it isn't, barely any, if at all!
I have also removed the engine cover to reduce heat...I like the mechanical look!

[The_Raging_Bull]

I'm not an an aero geek, but I'm a chemist. The pressure differential created by raming any air requires the system to be sealed. Last time I looked I can see pavement out of the engine bay bottom, so there's no way you're going to do harm under the hood, except to move additional cooling air into the bay, and push hot ai out the bottom.

My guess is it will aide in cooling the engine compartment better, a thermocouple and an electronic thermometer could answer that.

As for those of us who have CAI the possibility that you'll pull in hot under the hood air would be less with this as well.

Ater looking at their website, I hate to rain on any parades; but I favor not messing around too much with airflow and aerodynamics, which Chevy did a significant amount of time optimizing; I'd be interested in knowing EXACTLY how much their products affect the downforces of the car. Did they do any wind tunnel studies to come up with optimized products?

[Falundir]

On the aerodynamics.

Giving it thought, in theory I can only see it improving aerodynamics. You are removing a point of resistance that doesn't flow on the front of the car. Mind you the surface area is probably 2-3% of the whole fascia, but allowing air in vs stopping it with a solid surface and no where for it to go seems like a win to me.

However, I think the aero improvement would be measured in thousandths.

[The Stig]

Originally Posted by lgvenable

I'm not an an aero geek, but I'm a chemist. The pressure differential created by raming any air requires the system to be sealed. Last time I looked I can see pavement out of the engine bay bottom, so there's no way you're going to do harm under the hood, except to move additional cooling air into the bay, and push hot ai out the bottom.

My guess is it will aide in cooling the engine compartment better, a thermocouple and an electronic thermometer could answer that.

As for those of us who have CAI the possibility that you'll pull in hot under the hood air would be less with this as well.

Ater looking at their website, I hate to rain on any parades; but I favor not messing around too much with airflow and aerodynamics, which Chevy did a significant amount of time optimizing; I'd be interested in knowing EXACTLY how much their products affect the downforces of the car. Did they do any wind tunnel studies to come up with optimized products?

They probably didn't do any windtunnel testing. I understand that you can see the pavement from the bottom of the engine bay. But heat rises, so all that hot air is going to be trying to escape from the highest point in the engine bay. The only thing that will be going out the bottom is the cold air (unfortunately).

[Synner]

No you're increasing the drag coefficient by having it not flow around the car smoothly. That's why all the new special fuel efficiency packages on cars have shutters that close off openings at highway speeds.

[90503]

Not sure of the mail slot thing, but I bought (but haven't put it on yet) a "belly pan"...Was told it would actually make air circulate better for cooling in stock configuration of engine compartment instead of turbulence from below....and keep the engine compartment cleaner...dunno...

[CFD]

Remember that when Chevy first designed the front facia the mail slot was functional but by the time production came it was eliminated, for what reason I'm not sure.

Because the mail slot openning is so small any changes in airodynamics will have absolutely no measureable effect.

When I designed my mailslot scoop I chose to open the whole area not just the small openning behind the trim piece, this allowed for much more air flow. Although my scoop ties into my CAI it could easily be used to add air flow to the engine compartment but I felt the benefits of adding the additionional air to the intake was more beneficial.

[CFD]

Also something most don't take into consideration is that when your car is moving the air flow under the car acts a bit like a venturi and sucks the air out of the engine compartment

[The_Raging_Bull]

air coming in the front of the mail slot or the grills isnt going to just push out cold air, it'll push any and all air sitting in its way out the engine bottom.

The difference in hot and cold air is the density, but when a 60 to 90 mph airstream hits stagnant air, the higher velocity air is going to win > wheater its hitting cold or hot air. It'll also go the path of least resistance, i.e. towards the nearest open hole, so >> some toward higher openings, the rest towards the engine bottom.

Again, this is not a closed system; why over analyze it? If you want to spend 199.00 on this knock yourself out.


As the last commenter said, your're messing with the drag coefficients w/o knowing what you are doing. My point was Chevy DID wind tunnel testing, as the SS yeilds 160 lbs of upforce while the ZL1 has overall downforce (65?? lbs).

Frankly why mess with Chevy"s work unless it yields a way of feeding a CAI box directly, like the old shaker hoods, or directly to the TB thru a straight vararam style intake? That would get my money in a hurry.

[KBruno]

I never got an answer in their marketplace thread which was:

Originally Posted by KBruno

I love the idea of the mailslot being more than cosmetic but from the photos & renderings it looks like the air is diverted up directly into the rubber weather strip that seals against the hood & not down into the radiator area. Am I looking at it wrong? If the air is taken upwards do you cut the weather strip to let air into the engine bay or does it just flow around to the outside edges of the hood? Either way it seems the added function is purely cosmetic since either of those options wouldn't aid in cooling a water cooled engine in any way. Again, am I looking at it wrong?

Maybe it'll get read here or someone will pay attention. My opinion is that it's cute but should have been made to direct air into the radiator and not the hood seal. Also, a good extractor hood is good for both cooling & drag especially in conjunction with a belly pan (which shouldn't be used without the extractor). That's because the underside of the car is relatively 'dirty' aerodynamically campared to the top or sides of the car. But really, unless you drive at or above legal highway speeds for extended periods, aerodynamics play a very small part in overall drag.

[CFD]

Frankly why mess with Chevy"s work unless it yields a way of feeding a CAI box directly, like the old shaker hoods, or directly to the TB thru a straight vararam style intake? That would get my money in a hurry.[/QUOTE]

Utilizing the mailslot to feed a CAI is not that difficult, here are a couple of quick pics of how I did it

[Falundir]

Please excuse my ignorance, but wouldn't any vented hood also play with downforce?

[KBruno]

Originally Posted by Falundir

Please excuse my ignorance, but wouldn't any vented hood also play with downforce?

If well vented, and there are some poor designs out there, yes. But technically on the Camaro it'll reduce lift. It'll require more elements like the ZL1's complete aero package to get actual downforce.

[Synner]

Originally Posted by KBruno

I never got an answer in their marketplace thread which was:



Maybe it'll get read here or someone will pay attention. My opinion is that it's cute but should have been made to direct air into the radiator and not the hood seal. Also, a good extractor hood is good for both cooling & drag especially in conjunction with a belly pan (which shouldn't be used without the extractor). That's because the underside of the car is relatively 'dirty' aerodynamically campared to the top or sides of the car. But really, unless you drive at or above legal highway speeds for extended periods, aerodynamics play a very small part in overall drag.

I assume the goal is reduced underhood temps if you trim the weatherstripping. There's many Benfits to that for people who drive hard. And I don't understand your statement on aero doesn't play a role in drag, that's exactly what it does. A car at highway speeds uses 60% of its engine to counter drag so its extremely important. But the camaro has the aero of a Mac truck because their priority was retro design. So as I said a tiny opening will have negligible impact.

[geaux_tigerss]

Throw the overpressure idea out. There are too many outlets for this one little inlet to make any difference. Laughably so.

The drag thing is a non issue as well. Want to really change the airflow around a car? Open a window or sunroof. Much bigger opening.

[KBruno]

Originally Posted by Synner

I assume the goal is reduced underhood temps if you trim the weatherstripping. There's many Benfits to that for people who drive hard. And I don't understand your statement on aero doesn't play a role in drag, that's exactly what it does. A car at highway speeds uses 60% of its engine to counter drag so its extremely important. But the camaro has the aero of a Mac truck because their priority was retro design. So as I said a tiny opening will have negligible impact.

I fail to see any benefit at all with that little bit of air from the mailslot going over the radiator cap if you trimmed the weather strip. Through the radiator might help things that little bitty bit but since it's a water cooled engine it's not helping cool the engine when it's running and it won't cool the under hood when it's standing still. So what's the point other than cosmetic was my point there.

And I didn't say aero doesn't play a role in drag. I said "unless you drive at or above legal highway speeds for extended periods, aerodynamics play a very small part in overall drag". Depending on the car, tires including inflation pressure, road surface and other factors, an automobile uses more HP overcoming rolling resistance than aero drag up to anywhere from 40 to 60 MPH at which point they become equal. Above that point they both continue to rise, aero exponentially where rolling resistance is a liniar rise. Now, check your average speed on the information center. For most people that number is so low that aero drag played less of a roll than 1 or 2 lbs of tire pressure if that.

[edgehead2000]

Originally Posted by KBruno

Also, a good extractor hood is good for both cooling & drag especially in conjunction with a belly pan (which shouldn't be used without the extractor). That's because the underside of the car is relatively 'dirty' aerodynamically campared to the top or sides of the car.

Not following you on why using a belly pan without extractor is bad. Neither my old NA Chrysler Crossfire or their AMG tuned SRT6 had an extractor; regardless, it still performed beautifully.

[90503]

Originally Posted by edgehead2000

Not following you on why using a belly pan without extractor is bad. Neither my old NA Chrysler Crossfire or their AMG tuned SRT6 had an extractor; regardless, it still performed beautifully.

Yes, that's what I would like to know also...Of course the guy I bought the belly pan from said it's not a problem, but never heard it discussed here on the forums...So, I haven't put it on yet!...lol