Hood vents, Louvers, Scoops, etc - Engine Bay Heat Issues

NFRs2000NYC said:
Disclaimer....I am not a scientist nor am I an expert in aero/thermo dynamics....this is just information I have read over the years.....


When it comes to modern cars (and I use the word cars to describe vehicles) they are built to withstand the extremes of ALL temps, since they are marketed all over the world and engineering them for specific regions would be too costly...so, they must work in the winter in Norway or the summer in Dubai, in traffic, with the AC running, with black paint. To achieve this, generally speaking, the engine bay is designed using a low pressure system, so when you are moving, cold air (aka ambient air) is forced into the engine bay through the front grill, towards the top of the engine bay, thus, pushing the hot air down, which is then sucked out from underneath under the vehicle as you drive along. I have seen tests done with vented hoods on sports cars, and at speed (unless they were engineered with serious money behind it) the vented hoods would actually disturb the low pressure system, causing more heat to be trapped under the hood.

Now, when we are talking about stationary or very slow movement (ie, running a trail or crawling) then you go back to the basics of hot air rising, and in that case, a vented hood will indeed help you.

Just thought I'd throw that out there.
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I too am not an engineer by any means - but I think creating a plane of low pressure is the reason most of the vents in the PSC louver are (somewhat counterintuitively) facing backwards. The ridges that form the vent deflect airflow upwards, increasing its velocity. This increase in velocity creates a pocket of low pressure...which forms right above the opening. This is the same principle behind an airplane wing - the air deflected above the wing creates a lower pressure above the wing which helps keep the plane in the air. I think.
 
Mikead40 said:
I too am not an engineer by any means - but I think creating a plane of low pressure is the reason most of the vents in the PSC louver are (somewhat counterintuitively) facing backwards. The ridges that form the vent deflect airflow upwards, increasing its velocity. This increase in velocity creates a pocket of low pressure...which forms right above the opening. This is the same principle behind an airplane wing - the air deflected above the wing creates a lower pressure above the wing which helps keep the plane in the air. I think.
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From one non engineer to another, it would seem that at speed, cold air entering the grill now has an escape route and goes out the top, rather than get trapped and push hot air down. Again, I don't have the formulas or the equipment to prove any of this, just applying amateur knowledge to a complicated subject. :)
 
NFRs2000NYC said:
From one non engineer to another, it would seem that at speed, cold air entering the grill now has an escape route and goes out the top, rather than get trapped and push hot air down. Again, I don't have the formulas or the equipment to prove any of this, just applying amateur knowledge to a complicated subject. :)
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Yeah, I think we're saying the same thing - perhaps AEVs engineers say it best (second paragraph of the overview)

http://www.aev-conversions.com/shop/products/body-exterior/jk-heat-reduction-hood
 
Coming from the fast car world ( mostly fox body mustang GT's) every time I put a cowl hood on one, it did lower my under hood temps at least 5 degrees, and that was a great help when it came to multiply trips down the 1/4. Those temp drops where when a car ran 115 mph +, but I would think that at low speeds the draw though the hood scoop or vents would be much less do to not that much new air being forced into the engine bay. But like everybody else has said, I am by no means an engineer. I would just think it has to help at least at some sort of a speed over a crawl.
 
After reading this whole thread I thought I could chime in. I agree that most of the time louvers/scoops are used for looks but yes, they can be beneficial for any vehicle even the JK. A stock vehicle is engineered and designed to work how they are sold so If you do have problems with heat, 9 times out of 10 it will have nothing to do with venting the engine bay. Although, yes stock vehicles can overheat in certain conditions, i.e. 100+ degree days or being worked hard, i.e. off roading, pulling a trailer etc. And when you start modifying any vehicle you run the chance of needing to modify something else to compensate for it. For example LS swap jk, bigger engine being put into a space designed for a smaller engine. You have to find a way to keep it cool. But you may not need a vented hood depending on what else in in you setup i.e. radiator/fan etc. And yes, low speeds make it more difficult to expel heat. so in an off roading situation I can definitely see how it could be beneficial.

Now me personally, yes I think the louvers look cool, do I need the benefit of the extra cooling? not really because I haven't had problem with overheating. Plus being in Montana, it is cold. sometimes very cold for a majority of the year so I feel a vented hood wouldn't let the engine warm up as fast. Just my opinion though. But while off roading in the summer, it does seem to get very warm but it does not over heat. A vented hood would certainly help expel heat and keep it cooler and not hurt it in any way, but I feel I do not need to spend the money on it because I do not have any issues. Just my thoughts, I could be wrong but this is my justification for not owning a vented hood.
 
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Another thought that I don't think has been mentioned is that engines have specific temperature ranges to perform optimally and be the most efficient. Most likely varies depending on the engine and the parts that make it up. So ideally you want the temperature to be the closest to that range to get the most out of your engine. If a vented hood will get you to that temp for the conditions and purpose you are using your vehicle, yes there can be some benefits. Benefits that make big differences? I don't know, that's beyond my knowledge and comes down to research and testing.
 
I've got a smittybilt stingray hood (same style as 10a hood) and my eng temps have gone dow a fair bit. I've got the superchips trail dash and I noticed driving with my stick hood on in 90-100 degree weather that my temps would be around 220-230 now with this hood it's more like 210-220. IMG_5188.JPG


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rock lobster27 said:
I've got a smittybilt stingray hood (same style as 10a hood) and my eng temps have gone dow a fair bit. I've got the superchips trail dash and I noticed driving with my stick hood on in 90-100 degree weather that my temps would be around 220-230 now with this hood it's more like 210-220. View attachment 265446


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I put the same hood on and cut out the back of the louvers. I really haven't seen any reduction in temps though. It looks cool so I like it.


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Coop said:
I put the same hood on and cut out the back of the louvers. I really haven't seen any reduction in temps though. It looks cool so I like it.


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I also cut the backs out of the Louvers but I did remove my front inner fender liners not sure how much that helped.


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