My 70 dollar Heat Extractor Hood

[OnyxCobra]

that actually makes a lot of sense. I wish air didn't enter the engine bay, would be a lot easier to keep it clean. I can't see venting hot air with a heat extractor really doing anything then either, if moving air around the engine bay doesn't help with cooling.

 

[ReplicaR]

Heat extractor hood does not vent anything. It extracts the used up hot air out of the engine bay. Once the air has gone through the radiator, it's trapped in the engine bay until it can build up enough pressure to exit either through the bottom of, ending up under the car, generating more lift in the process, or through gaps around the hood panel. Heat extractor takes that air, and helps it exit through the hood. This has a few positive effects, one being that you increase downforce by reducing the amount of air that goes under the car, and increasing the amount of air that goes over the car. Another one is that since the air is no longer trapped under the hood to a certain extent, it's no longer working against the air going through the radiator, and helps with cooling.

 

[duff daddy]

So by doing a heat extractor hood, you actually lower your car :tard:

 

[ReplicaR]

hehe, not quite. A well designed front end aero package will only put a slight amount of downforce on the front, which will still feel like a big difference, since stock it's just a massive amount of lift.

 

[ttocs]

I had always assumed that they cooled themselfs with a venturi effect to make the air passing over the holes create a pressure to suck the air out. You do not need air forced into the front of the motor to get air out of the engine bay. while it is moving over the vents/holes the venturi effect of the air going over the vent will make it draw air out of the bay. ever blown air over a staw in some liquid? The fluid will be pushed to the top of the straw, blow hard enough and it will come out.

I have seen the heat waves comming out of even the stock hood holes while it is not moving so to say that they do not evacuate any heat at all seems a little bit off to me. I don't think it will make the car significantly cooler but ever bit helps.

 

[ReplicaR]

I've never said that you need to push the air through the front of the car to make the heat extractor work. What I've said, is that the most efficient way to channel the air through the radiator is to have it in a sealed tunnel. It will pick up air in front, pass it through the radiator, and then dispose of it somewhere in a nice open space, preferably over the car. Another thing I did not say is that the opening does not expel the heat. I've said that at speed, it will suck the air in because it's a high pressure zone. When you are standing still, there are no pressure, because there is no air moving over the car. This way any hole will expel heat. Hell, no hood at all will be the best way to expel heat, right?

It is very hard to point to one simple fact, and say that this is what's mainly causing the effect. Just like anything else automotive, proper cooling is a combination of things, such as air flow, heat exchange efficiency, pressure zones. You have referred to Venturi effect, which if I remember correctly has to so with speed of air and amount of pressure it will generate. I may have not referred to it as such, but I've talked about pressure zones for a very long while now. I will explain it again, using visual aid this time.

Above is a picture of pressures generated by wind tunnel testing on a C6R. As you can see the bits of the car which face the most against air are the ones which generate the highest pressure. The highest ones are on the very front of the vehicle and the cowl section, where the flow angle changes dramatically. The green parts are the ones with the lower pressure. Now, according to the Venturi effect that you have brought up, higher pressure will push the air into the zones with lower pressure. What this means is that at speed the air that hits the cowl will be in a high pressure zone. The raised part of the hood would generate a low pressure right behind it. Air will go anywhere and everywhere it could possibly fill. So, you've got high pressure zone right at the cowl, and a low pressure zone right behind the opening of the hood. Guess where some of that airflow is going to go?

I'm not going to bother trying to explain this any further. There are tons of online articles which explain how the aero works, and why the heat extractors are place where they are. If you don't want to believe me, you are free to do whatever you want. It's a free country, so you can go ahead cut up the hood in the back, or run with no hood at all, because more is better right?

 

[OnyxCobra]

I think all of this air flow management is more or less negligible when talking about our Mustangs. I don't believe these cars will benefit as much from a heat extractor hood as a cowl induction hood would hurt it.

 

[ReplicaR]

Well, that's what I intend to find out.

 

[g36 monkey]

Thats not a mustang in that picture ;p

Just keeding, dude knows his stuff ha.

 

[ttocs]

please do not think I am arguing to calling you wrong, I am debating and learning.

Venturi effect(for air) means passing air across a small tube/opening, which has a much larger cavity and opening behind it. For this example I do not think the heat extractor hood would count as the opening in the grill and the extractor are almost the same size so the only air out of it will be heat rising when standing still and when moving if the air is pushed from the grill(as your example shows). The venturi effect would be more for the stock hood. The two little holes on top open up to a large hole on the bottom under the hood blanket(which would restrict it). When driving and air is passed across those holes they creat a low pressure area inside the hood that will suck the heat out from the larger hole underneath. You see this cooling used often on prop planes as or even on rc airplanes where there will be a hole on the bottom of the cowl covering the motor to draw heat out. you can prove this works like I said above with just a straw and some liquid. Cut the straw not completely in half but so that you can bend it into a 90 degree angle. Now put the straw in some liquid while still at 90 degrees and blow through the one piece, across the piece that is in the liquid. When doing this the low pressure will cause the liquid to suck up into the straw above the water level.


make any sence? Again just playing devils advocate to learn a little bit. I am an electronics person and by no means a rocket surgon so....

 

[evilcw311]

having the termi style heat extractor hood on my 95 i have seen a bit of a cooling effect on my motor, but thats obviously way different than a cowl as you guys are talking of. mine is basically flowing jsut as the pic that replica just posted up above. now obviously i did it the expensive way by jsut ordering the hood already built but i honestly have seen a difference. we played around with a remote meat thermometer with my old hood and then the h.e. hood and seen anywhere from a 20d drop to upwards of 80d drops depending on if we were in town and on the highway. so i dont know if that helps you guys decide on validity of a true h.e. style hood or not but it seems that for mine it is well worth it, only downfall is the rain getting on my belt when the car sits still in the rain. i have to make some cover plates for rainy days.

 

[OnyxCobra]

a meat thermometer? where did you put it?

 

[evilcw311]

wire tied it to the wire harness close to the firewall. its just a remote probe and then you have the reader in the car. its one of the ones where you can monitor a steak on the grill from inside the house.
I know its nowhere near an exact science but we did it on two days with almost identical weather. to show that much of a difference has to prove something plus my coolant gauge has also reflected cooler run temps. im not saying that its a cure for cars running hot but in the heat that we've had this summer it is a noticable difference.

 

[OnyxCobra]

I refuse to believe a heat extractor hood on our cars would actually help the car run cooler under normal driving conditions, even on a track I have my doubts.

 

[ttocs]

why would you doubt that more air = good = cooler? Cover your grill and lower valance as small as they are and what would happen? I could see it doing 10-20 degrees difference and if he said he did it and those are the results I believe him.

 

[evilcw311]

well arent we just the pesimistic one tonight!!!!???!!!?!?! lmao jk

i bought the hood just because i thought it would look sick on the car. i didnt buy it for functionality, but after playing around with both there is a noticable difference.
if it cant help at all then why did ford put that hood on the termi's from the factory and on other models since then??? that would be my only question towards that.

 

[ttocs]

even just under idle, the hot air would be able to rise out better, let alone under movement. Guess you will need to mount the old hood and then do your experiment again and take pics or it didn't happen here right ?

 

[evilcw311]

problem being that hood went bye bye. if anyone wants to meet up that has a stock hood id be more than happy to do it again with vid or pics.

 

[ttocs]

you could always just cover up the hole as well to see the difference. I mean if a big hole makes no difference, then I would assume no holes would make no difference either just to prove your point.

 

[evilcw311]

i need to make a set of plates to cover the holes on rainy days anyways. it should have the same effect as having the stock hood back on it then. when i get time to do that ill have to make vids or pics.