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Old 08-09-2014, 10:46 AM   #1 (permalink)
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Radiator hood vent?? Aero, cooling, WAI, all in one??

Off and on lurker as I research my crazy ideas... I hope this is the best section for this, if not hopefully an admin or mod can move it to the appropriate section.

In many high end vehicles you see hood vents at about the break over point of the hood, I'm assuming this is the start of the pressure zone in regards to air flow (see image 1). And in some extreme race cars and high speed vehicles this is actually the exhaust/exit for all air allowed through the front of the car for the cooling system. It is a sealed "chute" or tunnel from the air dam/bumper through the rad/intercooler/etc and then out the hood (see image 2). It's almost always used in hill climb and time attack cars to maximize cooling with the super high powered and boosted engines. Couldn't this be easily adapted for ecomodding to utilize a front air dam (or blocking of all other openings in bumper) and maintain cooling (see image 3 & 4)? Wouldn't this allow for better control of front aero/resistance by channeling the incoming air and removing engine bay resistance (possibly combined with belly pan), engine temps would be kept low in the face of overly hot engine compartment temps, and create a warm air environment suitable for removal of filter box and modification to cone filter, removing the need to fabricate a WAI? I'm not sure if I'm truly explaining myself, but I hope that made sense. Images 5-10 are of builds done on various cars and engine configurations. The AMS build changes the orientation of the rad, the second Mitsu build maintains stock orientation. I feel like the design for the mitsu could be modified for most Fwd engine compartments. I hope it's ok that I linked to other sites/forums, I'm not affiliated with any of them... Just wanted to give appropriate credit to someone else's work.

I look forward to hearing from some of you ecomodding and aero experts!!!

~C


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Following images found here Radiator Hood Vent - Miata Turbo Forum - Turbo Kitten is watching you test compression.
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Following images from here The AMS Unlimited AWD TA EVO X build! - - Page 3 - Time Attack Forums

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following pictures from My ducted radiator setup - road racing | Page 4 | DSMtuners

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Old 08-09-2014, 11:33 AM   #2 (permalink)
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Interesting.... I assumed you were going to mention the reverse cowl hood like you see on many v8 powered vehicles or the hood vent like you see on a hummer. I think in the hummer the radiator maybe horizontal vs vertical so if someone takes a shot at the grill it wont suffer an instant water leak.



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Old 08-09-2014, 12:03 PM   #3 (permalink)
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Quote:
Originally Posted by Cobb View Post
Interesting.... I assumed you were going to mention the reverse cowl hood like you see on many v8 powered vehicles or the hood vent like you see on a hummer. I think in the hummer the radiator maybe horizontal vs vertical so if someone takes a shot at the grill it wont suffer an instant water leak.

It was my understanding that cowl *induction* hoods are for sucking in cooler air that forms a high pressure pocket at the windshield and not for actual ventilation of the engine compartment? This would seem to be counter productive from a W.A.I. as well as an aerodynamics standpoint.

That being said, I like cowl hoods, and perhaps you would adapt a cowl type structure to better control the flow of exiting air and deal with rainwater/foreign objects falling down the hood chute. Rather than a cowl for venting/inducting cooler air to the bay, the cowl would just be the exit of the radiator air flow.

Hadn't considered the idea of a minor fender bender instantly cracking you radiator or worse... I suppose one could incorporate a crumple zone into the lower chute? Maybe use thin ABS plastic that will flex with some sort of fabric wrap to keep air from leaking at the seams?

~C
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Old 08-09-2014, 01:11 PM   #4 (permalink)
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I would paraphrase your question as 'do best practices in the race car field apply to ecomodding?' Close enough?

Your question could use some more context (like you pic #1). Ecomodding extends from someone looking for pay-back within x000miles, to some one building their own reverse tricycle. Here's you theoretical ideal:



The size of the ducting package isn't trivial. Also, immersing the engine itself in turbulent moving air has to provide some degree of engine cooling; sealing it in a close compartment should throw more load onto the water cooling subsystem.

Consider the warm air intake. One has to admit sufficient air to supply the intake. So the radiator and induction have to be outside the sealed compartment.

There are other threads that suggest the bottomside or wheelwell as the best place to dump the radiatored air.
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Old 08-09-2014, 05:10 PM   #5 (permalink)
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Quote:
Originally Posted by freebeard View Post
I would paraphrase your question as 'do best practices in the race car field apply to ecomodding?' Close enough?
Not per say... Most race car practices pertain to downforce, ventilation of hot air, and cooling of brakes/drivetrain/engine under extreme stress. The goals of their practices are not in line with that of ecomodding. As best I can tell. BUT a difference in goals doesn't mean that their ideas can't work for ecomodding.

Paraphrase would be "can one utilize these particular ideas to accomplish multiple goals in a more efficient and safe fashion than one can with more common ecomods?"

When one blocks airflow in the front of the car, a common ecomod, you risk dangerous engine temps due to lack of airflow to both ventilate the engine compartment and to optimize the cooling system. I have seen this discussed many times on this site. Utilizing radiator ducting, one can do this in a manner which still allows one to maintain lower engine temps (I would assume). As long as the radiator wasn't confined and you didn't delete your fan, it should maintain in stop and go traffic as well shouldn't it? This would also give you a greater ability to block and smooth more of your bumper/airdam.

Quote:
Your question could use some more context (like you pic #1).
Context:

Pic#1 is of common ventilation points on many higher end cars. It falls just behind the nose of the hood where frontal impact begins to dissipate. If you drive in the winter, it's the point where road grime begins to give way to a clean hood.

examples of the "line" or "break over" point I'm referring to:

Between the dark blue and the green on the hood, this is the area I was pointing out.


Most modern day factory hood vents are at this point, just as they are in pic #1 from my original post. That was the hood of a BMW.



Quote:
The size of the ducting package isn't trivial. Also, immersing the engine itself in turbulent moving air has to provide some degree of engine cooling; sealing it in a close compartment should throw more load onto the water cooling subsystem.
True, and thanks for that diagram, very good addition to the conversation!!! It will indeed throw more load onto the cooling system. However, rather than letting random air come through and kind of help cooling, you are supercharging your cooling system by force feeding it the air from the duct. Surely this same modification could compensate for higher engine bay temps with an unmodified engine which is driven under incredibly low stress circumstances?? I don't claim to know this, it's why I started this thread

Quote:
Consider the warm air intake. One has to admit sufficient air to supply the intake. So the radiator and induction have to be outside the sealed compartment.
Amateur roadracers, utilizing belly pans and restricted air intake from the bumper routinely see increases in cooling capabilities via radiator ducting like this. That's with bigger turbos, hotter engines, higher revs, and the same "sealed" situation you are discussing. Some of them place the intake in the ducting, some run CAI below the engine or to the wheel wells, some just leave an exposed filter in the "sealed" engine bay. If one was truly worried about it, they could incorporate small round ducts from the bumper to the engine compartment or create ducts to/from the wheel wells to ensure the engine didn't "suffocate". One could also incorporate a small cowl induction system. However, all of these ideas would be bringing in "cooler" air, not sure how much of a negative impact this would have on the warmer intake temps. But even vented in such a manner, the temps should be warmer than stock??? Ultimately, even with a belly pan, radiator ducting, and air dam, the compartment is far from being truly sealed.

Quote:
There are other threads that suggest the bottomside or wheelwell as the best place to dump the radiatored air.
I have read those, especially a lot of the talk around the modded aerocivic by basjoos. I would be curious why you would vent under the car when so many people go out of their way to experiment with full length belly pans, rear diffusers, etc to smooth and control the flow under the vehicle. Same with the wheel well considering so many try to seal the wells and keep air out of it? Wheel wells would make sense to me if you vented behind the wheel, using the rad exflow to force air out of the well, and then an airblade or vent wall to straighten the airflow to follow the side of the vehicle without disrupting the flow around the car. Again, most of this knowledge I have taken from these very forums... I don't claim to know anything, I just read a lot hahaha.

Lets look at this again:


The green areas in front of the bumper and the lower windshield... Couldn't one, via radiator ducting and hood vent, make those areas into higher flow areas? Wouldn't this decrease wind resistance and increase airflow in the two biggest spots of resistance? This would in effect, decrease frontal load on the vehicle would it not? Allowing the air to flow straight through, and then pop out of the hood at an angle which could assist the air in flowing over the windshield. I'm just thinking out-loud at this point though. This wasn't the original intent behind my post



~C
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Old 08-09-2014, 05:52 PM   #6 (permalink)
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1) COLD air is DENSER than HOT air.

2) HOT (less dense) air from radiator will RISE.

3) HOT (less dense) air has lower viscosity and thus clings LESS to surfaces.

HINT -- view a radiator as being a low-temperature example of a ram-jet engine: cold air IN & hot air OUT = THRUST.

Last edited by gone-ot; 08-09-2014 at 10:34 PM..
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Old 08-09-2014, 05:59 PM   #7 (permalink)
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Quote:
Originally Posted by Old Tele man View Post
1) COLD air is DENSER than HOT air.

2) HOT (less dense) air from radiator will RISE.

3) HOT (less dense) air has lower viscosity and thus clings LESS to surfaces.

HINT -- view a radiator as being a low-temperature example of a ram-jet engine: cold air IN & hot air OUT = THRUST.
So you're telling me my radiator ducting becomes a secondary form of propulsion as air flies out the hood?
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Old 08-09-2014, 08:39 PM   #8 (permalink)
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My mention of pic#1 was distracting; I meant what range of vehicles are you considering. I assume front-engined and water cooled.





Here are some mid- and rear-engined examples that might be instructive.

Under the skin the structure of the Toyota racer is remarkable similart to a long A-arm off-road racer. F1 cars also use a high pointed nose tip, overhanging their front wing.

The Porsche Boxter uses two radiators in front of the wheels. They also cheat the duct length-equals-radiator-height rule of thumb with deep pockets for wind tunnel hours.

Old Tele man is probably thinking of the P-51 Mustang that got measurable thrust from the cooling sustem.

Meredith effect - Wikipedia, the free encyclopedia

Quote:
If the generated thrust is less that the aerodynamic drag of the ducting and radiator, then the arrangement serves to reduce the net aerodynamic drag of the radiator installation. If the generated thrust exceeds the aerodynamic drag of the installation, then the entire assemblage contributes a net forward thrust to the vehicle.
(Adding the cowl hood scoop to your race car ducting would add skin friction and exit in a high pressure area.)
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Old 08-09-2014, 11:37 PM   #9 (permalink)
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So you're telling me my radiator ducting becomes a secondary form of propulsion as air flies out the hood?
Apparently it was worth several mph on the P51 fighter back in WWII, enough that they studied and optimized the effect. I don't have a reference handy but I think one or more of the NACA papers at the NASA archive deal with this. On a car at 55 mph, who knows :-).
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Old 08-09-2014, 11:56 PM   #10 (permalink)
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Quote:
Originally Posted by chillsworld View Post
So you're telling me my radiator ducting becomes a secondary form of propulsion as air flies out the hood?
If you have enough heat differential, the answer is "yes," otherwise it's "no."

This is what the P51D Mustang combined oil/air-intercooler assembly really looked like:



...and this was the NACA analyses for the combined air flow:



Last edited by gone-ot; 08-10-2014 at 12:13 AM..
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