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Discussion Starter #1
Does anyone know if the hellcat heat extractor hood is effective at reducing engine temps?

Or is it more just for looks?

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Does anyone know if the hellcat heat extractor hood is effective at reducing engine temps?

Or is it more just for looks?

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I think it is. I can see the heat coming out of my car when I'm sitting still from the vents. It looks like a B2 bomber from the driver's seat

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Does anyone know if the hellcat heat extractor hood is effective at reducing engine temps?

Or is it more just for looks?

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While I would like to believe there is some benefit to the vents there may not be. I have toyed with the idea of using wax to stick a bunch of short strings of yarn around the hood vents to help determine the air flow at idle and when the car is moving. Have not done this yet.

Even if the vents are not there solely for show they are not really going to have much effect on engine temperature, at least directly.

The engine is water cooled and air flowing past the engine just can't remove much heat.

Besides a copious amount of air that has passed through the radiator, and which has picked up the heat from the hot coolant, flows into the engine compartment.

While the vents could allow air flow from above the hood down into the engine compartment the last thing one wants to do is give air another way to flow into the engine compartment that has it bypassing the radiator.

This just doesn't make any sense.

With the car stationary and the radiator fan operating some air could flow out the vents. The engine compartment would be under some -- slight -- positive pressure.

If there is any air flow through the vents when the car is moving it would have to be out of the engine compartment.

As I touched upon above there is at least one good reason that air not flow into the vents and into the engine compartment at any time.

The air would flow out of the vents when the car is moving due to the creation of a low pressure area above the vents. Given their location and that they are depressed I'd hazard a guess they are located in a low pressure area.

With a big radiator which is obviously needed to deal with the heat load the Hellcat engine produces and given the speed the car can obtain considerable air flows into the engine compartment and must exit equally fast to avoid creating a high pressure area in the engine compartment which could interfere with the critical flow of air through the radiator. Thus the vents would act at speed to give the air some of the air in the engine compartment an exit to keep the air pressure in the engine compartment lower to help air flow through the radiator.
 

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I'd venture that on a Hellcat, there's a need to move more underhood air out - you have
intercooler
air to oil cooler
transmission cooler (both M6 and A8)
thare are in the front fascia these all are radiating heat from the various fluids in additional to the main cooling system radiator - under boost, the 6.2 'Cat engine is going to put out a lot more heat.

For a stock N.A. engine, it may contribute some benefit, but the demands for cooling are nowhere as great as the 'Cat would be.
 

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I can see your point & from what your saying it would help with heat. If they are there to get the engine bay air out then it has to be dragging the hot air out as well from what your saying. I know they when I am sitting (fans off) I can see the heat coming out of my hood & when the fans come on I can feel the heat being pushed out of them. The only way to know would be if u had the thermal camera I guess.

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Discussion Starter #6
While I would like to believe there is some benefit to the vents there may not be. I have toyed with the idea of using wax to stick a bunch of short strings of yarn around the hood vents to help determine the air flow at idle and when the car is moving. Have not done this yet.

Even if the vents are not there solely for show they are not really going to have much effect on engine temperature, at least directly.

The engine is water cooled and air flowing past the engine just can't remove much heat.

Besides a copious amount of air that has passed through the radiator, and which has picked up the heat from the hot coolant, flows into the engine compartment.

While the vents could allow air flow from above the hood down into the engine compartment the last thing one wants to do is give air another way to flow into the engine compartment that has it bypassing the radiator.

This just doesn't make any sense.

With the car stationary and the radiator fan operating some air could flow out the vents. The engine compartment would be under some -- slight -- positive pressure.

If there is any air flow through the vents when the car is moving it would have to be out of the engine compartment.

As I touched upon above there is at least one good reason that air not flow into the vents and into the engine compartment at any time.

The air would flow out of the vents when the car is moving due to the creation of a low pressure area above the vents. Given their location and that they are depressed I'd hazard a guess they are located in a low pressure area.

With a big radiator which is obviously needed to deal with the heat load the Hellcat engine produces and given the speed the car can obtain considerable air flows into the engine compartment and must exit equally fast to avoid creating a high pressure area in the engine compartment which could interfere with the critical flow of air through the radiator. Thus the vents would act at speed to give the air some of the air in the engine compartment an exit to keep the air pressure in the engine compartment lower to help air flow through the radiator.
Why do you say you dont want more air into the engine bay if it hasnt passed over the radiator?

Air flow that bypasses the radiator and enters through the heat extractors (at speed is going to be minimal) has to be cooler then the air in the engine bay though, its seems like any cooler air would be good, even if it is minimal. However I would think at any speed over say 10 mph isnt going to actually go into the engine bay, it is likely creating a vacuum or low pressure as you mentioned, above the extractor and pulling air out of the engine bay and that engine bay air is hot. I see it pulling more air (hot) out then actually letting cool air in. To bad physics class was over 24 years ago maybe I would have a clearer picture.

Stationary Car: Hot air rises, the air in the engine bay is hotter then the outside air and therefore will escape the engine bay without a radiator fan being on, no positive pressure needed. I often and I am sure it isnt needed but when I park in the garage after driving around on a hot day I will leave the garage door open and pop the hood for a while to help move the hot air away from the engine quicker. I cant imagine it is a bad thing to do.

The top speed of the Hellcat is what like 11 MPH more then the SRT 392? Now of course the SRT 392 doesnt have some of those extra cooling bits or a SC to create more hot air in that engine bay but as far as speed goes I would think those vents would also help keep the air pressure in the engine bay of the SRT 392 lower as well.

I am not tracking (probably never) or drag racing my car regularly so I know that I dont really have a problem with the heat in the engine bay affecting performance. I guess I was more thinking that any extra heat I can remove from the engine bay would be a good thing, maybe even if that is just for longevity of the engine itself. I know its not more important then regular scheduled maintenance and what not but heat to much excessive heat can be bad for engine life, things wear out faster, so why not help cool the engine off even if only by a couple degrees.
 

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The Demon and 2019-up Hellcats eliminated them. They probably didn't hurt but doubt they needed them.


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Not to mention the red-eye puts out more power than the earlier HC versions and does not have heat extractors. Wonder if 2 scoops or the demon single scoop have something to do with not having to run the heat extractors?
 

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Demon and 2919-up Hellcat hoods have no extractors, why not?


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The demon had a grabber hood so all the air they went in was sucked in to the engine. I think one side of the hellcat hood pulls air into the engine bay.

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The demon had a grabber hood so all the air they went in was sucked in to the engine. I think one side of the hellcat hood pulls air into the engine bay.

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Right, but neither has extractors so FCA didn't feel they were mandatory. So like I said, they don't hurt but are not needed and I'm sure looks had a lot to do with it.



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Right, but neither has extractors so FCA didn't feel they were mandatory. So like I said, they don't hurt but are not needed and I'm sure looks had a lot to do with it.



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Makes sense on all parts.

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Why do you say you dont want more air into the engine bay if it hasnt passed over the radiator?

Air flow that bypasses the radiator and enters through the heat extractors (at speed is going to be minimal) has to be cooler then the air in the engine bay though, its seems like any cooler air would be good, even if it is minimal. However I would think at any speed over say 10 mph isnt going to actually go into the engine bay, it is likely creating a vacuum or low pressure as you mentioned, above the extractor and pulling air out of the engine bay and that engine bay air is hot. I see it pulling more air (hot) out then actually letting cool air in. To bad physics class was over 24 years ago maybe I would have a clearer picture.

Stationary Car: Hot air rises, the air in the engine bay is hotter then the outside air and therefore will escape the engine bay without a radiator fan being on, no positive pressure needed. I often and I am sure it isnt needed but when I park in the garage after driving around on a hot day I will leave the garage door open and pop the hood for a while to help move the hot air away from the engine quicker. I cant imagine it is a bad thing to do.

The top speed of the Hellcat is what like 11 MPH more then the SRT 392? Now of course the SRT 392 doesnt have some of those extra cooling bits or a SC to create more hot air in that engine bay but as far as speed goes I would think those vents would also help keep the air pressure in the engine bay of the SRT 392 lower as well.

I am not tracking (probably never) or drag racing my car regularly so I know that I dont really have a problem with the heat in the engine bay affecting performance. I guess I was more thinking that any extra heat I can remove from the engine bay would be a good thing, maybe even if that is just for longevity of the engine itself. I know its not more important then regular scheduled maintenance and what not but heat to much excessive heat can be bad for engine life, things wear out faster, so why not help cool the engine off even if only by a couple degrees.
All air that enters the engine compartment should come through the radiator. Any air that comes in from some other source can increase air pressure in the engine compartment and impede air flow through the radiator. It is the air flow through the radiator and the cooling it does to the coolant the keeps the engine cool. The air that passes through the radiator flows down and out of the engine compartment. This has it flowing by the exhaust manifolds which emit considerable heat. I have seen hard running engines with the cast exhaust manifolds at dull red temperature. With "headers" -- thinner walled tubing -- the headers can glow a brighter red.

The concern is (maybe) at some speed the engine compartment can't handle the volume of all the air that comes through the radiator. Thus extra air exhaust vents in the hood provide another exit to prevent air pressure at speed from impeding air flow through the radiator. This increase in air pressure could be sufficient to make the front of the car light and affect high speed stability and handling. With a top speed of around 200mph at some point a Hellcat is as much a vehicle of the air as of the ground. In this case though the desire is to keep the Hellcat firmly on the ground.

Thus I would be surprised if air flows from the outside through the vents into the engine compartment.

Now I agree that with the car stationary and the radiator fan running I would expect air to flow out the vents.

One concern would be to have hot engine compartment air exiting the hood could result in the cabin air intake vents pulling some of this air in. That is not good. Now without the benefit of being able to observe the hot air from the vents and with the cabin vent fan running maybe this is not a concern. The air is hot enough that it rises rather quickly and is well out of "reach" of any pull the cabin vent fan might have.

This is probably the case as I have been in my Hellcat in really hot ambient temperature with it stationary and with the cabin vent fan running at high speed and have never smelled engine compartment.

The increase in the volume of air flow through some opening is not linear with speed thus one can't really consider the 11mph difference just "11" in terms of the additional amount of air that needs to flow through the radiator and out the engine compartment.

The control of engine compartment heat with speed is taken care of automatically. With more speed the engine produces more heat. But with more speed there is more air flow through radiator and into the engine compartment. The generation of heat and its removal are in balance. Otherwise at some speed the engine, its cooling system, would experience thermal overload and I'm sure if this was the case we'd know about it by now.
 

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The Demon and 2019-up Hellcats eliminated them. They probably didn't hurt but doubt they needed them.


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It could be just marketing. Anything to make the newer car appear different from the older model cars. Then after a year or two the vents or something like them make a come back to make the previous models without them look "old".
 

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The Challenger SRT Hellcat hood is made of light, strong military-grade aluminum. Many people are surprised to learn that none of the three surface openings feed air directly into the SRT Hellcat’s supercharger intake tract. Though the center opening resembles the carburetor air feed scoop first seen on the 1970 AAR ‘Cuda as well as certain SRT Vipers, on the Challenger SRT Hellcat, the center opening serves to cool the engine bay. The outer openings extract under-hood heat from the intercooler and are also placed specifically to release air trapped at high speed. Without them, the trapped air would collect under the hood skin and cause the front of the car to lift, contributing to drag and reducing the front tire contact patch. But there’s more. Once released to the slipstream of air flowing over the body of the car, the volume of air flowing out of the three hood vents meets the base of the sloped windshield where it exerts added downforce. Dodge brand engineers spent many months inside the Auburn Hills wind-tunnel test facility optimizing the sizes and shapes of these openings.

A look at the underside of the SRT Hellcat hood completes the picture. The author points out how the center opening admits cool, dense outside air into the engine bay. Supercharged engines like the SRT Hellcats are more sensitive to elevated operating temperatures than naturally aspirated engines. Without extra attention to the overall cooling system, heat soak can trigger computerized onboard vehicle sensors to step in with reduced ignition timing and reduced power delivery when you really need it. Not the SRT Hellcat. The dark padding absorbs sound and vibration.


A Guy
 

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The Challenger SRT Hellcat hood is made of light, strong military-grade aluminum. Many people are surprised to learn that none of the three surface openings feed air directly into the SRT Hellcat’s supercharger intake tract. Though the center opening resembles the carburetor air feed scoop first seen on the 1970 AAR ‘Cuda as well as certain SRT Vipers, on the Challenger SRT Hellcat, the center opening serves to cool the engine bay. The outer openings extract under-hood heat from the intercooler and are also placed specifically to release air trapped at high speed. Without them, the trapped air would collect under the hood skin and cause the front of the car to lift, contributing to drag and reducing the front tire contact patch. But there’s more. Once released to the slipstream of air flowing over the body of the car, the volume of air flowing out of the three hood vents meets the base of the sloped windshield where it exerts added downforce. Dodge brand engineers spent many months inside the Auburn Hills wind-tunnel test facility optimizing the sizes and shapes of these openings.

A look at the underside of the SRT Hellcat hood completes the picture. The author points out how the center opening admits cool, dense outside air into the engine bay. Supercharged engines like the SRT Hellcats are more sensitive to elevated operating temperatures than naturally aspirated engines. Without extra attention to the overall cooling system, heat soak can trigger computerized onboard vehicle sensors to step in with reduced ignition timing and reduced power delivery when you really need it. Not the SRT Hellcat. The dark padding absorbs sound and vibration.


A Guy
Well there u have it. Lol

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The Challenger SRT Hellcat hood is made of light, strong military-grade aluminum. Many people are surprised to learn that none of the three surface openings feed air directly into the SRT Hellcat’s supercharger intake tract. Though the center opening resembles the carburetor air feed scoop first seen on the 1970 AAR ‘Cuda as well as certain SRT Vipers, on the Challenger SRT Hellcat, the center opening serves to cool the engine bay. The outer openings extract under-hood heat from the intercooler and are also placed specifically to release air trapped at high speed. Without them, the trapped air would collect under the hood skin and cause the front of the car to lift, contributing to drag and reducing the front tire contact patch. But there’s more. Once released to the slipstream of air flowing over the body of the car, the volume of air flowing out of the three hood vents meets the base of the sloped windshield where it exerts added downforce. Dodge brand engineers spent many months inside the Auburn Hills wind-tunnel test facility optimizing the sizes and shapes of these openings.

A look at the underside of the SRT Hellcat hood completes the picture. The author points out how the center opening admits cool, dense outside air into the engine bay. Supercharged engines like the SRT Hellcats are more sensitive to elevated operating temperatures than naturally aspirated engines. Without extra attention to the overall cooling system, heat soak can trigger computerized onboard vehicle sensors to step in with reduced ignition timing and reduced power delivery when you really need it. Not the SRT Hellcat. The dark padding absorbs sound and vibration.


A Guy
That's good info. Thanks.

Added: But does the Demon hood scoop also direct any air into the engine compartment? And the same question for the 2019+ Hellcats and REs.
 

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Discussion Starter #19
I agree good article. I now somehow feel like the SRT 392 is the red headed step child of the group of challenger models though. Or like the franken model bastard child. LOL

Reasons
SRT 392 only got the center scoop which I have now learned is for cooling not feeding air to the engine. No heat extractors cause it is not a hellcat and does need the added benefit of additional cooling for the supercharger which is more sensitive to high temps.
It sounds like it the extractors could be useful at high speed to remove trapped air, again top speed of a hellcat and SRT392 not that far off, why didnt the SRT392 get the "extractors"?
SRT 392 did not get the headlight tube air intake that is on the hellcat. Not supercharged probably doesnt needed the added air but according to the article the other models got "scoops" that feed the air to the engine. So why did the SRT392 get something to feed air into the engine?
 

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I think 707 was very important to SRT when the Hellcat was developed. Not 700HP, or around 700HP...but 707HP, so there was no doubt there was an "over 700HP" engine in the beast.

A Guy
 
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