Vented hoods and turbos

[Midtenn]

Raising the hood and/or removing the weather strip isn't going to help the cooling at speed. The base of the windshield is a high pressure area, so as speed you are going to force air back into the engine bay.

Since the engine bay is already a high pressure area, you want to use a low pressure area to "pull" the air from under hood out of the car. Looking at this velocity plot from Hancha Group, you'd want to have the vents in the red area of the hood. From what I've seen in other plots of theirs (on Miatas) the green is high pressure, low speed air. I'm sure they could shed much better light on this than me.

[DJCarbine]

Originally Posted by Midtenn

Raising the hood and/or removing the weather strip isn't going to help the cooling at speed. The base of the windshield is a high pressure area, so as speed you are going to force air back into the engine bay.

Since the engine bay is already a high pressure area, you want to use a low pressure area to "pull" the air from under hood out of the car. Looking at this velocity plot from Hancha Group, you'd want to have the vents in the red area of the hood. From what I've seen in other plots of theirs (on Miatas) the green is high pressure, low speed air. I'm sure they could shed much better light on this than me.

As long as fresh air is entering then it would still be functional, its the lack of air movement (and heat) that people are concerned about
Also the green low pressure area is right at the hood cowl it appears, so it should create a low pressure area for air from the hood to vent from. Hopefully that will also mean the possibility of more air moving past your intercooler/radiator

[Sellout]

Originally Posted by DJCarbine

As long as fresh air is entering then it would still be functional, its the lack of air movement (and heat) that people are concerned about
Also the green low pressure area is right at the hood cowl it appears, so it should create a low pressure area for air from the hood to vent from. Hopefully that will also mean the possibility of more air moving past your intercooler/radiator

It looks like the cowl area is less pressure than what's in front of the radiator, of course, but it'll never be as effective as hood vents underneath that red area on the hood, which will also result in more air through the radiator.

[DJCarbine]

Originally Posted by Sellout

It looks like the cowl area is less pressure than what's in front of the radiator, of course, but it'll never be as effective as hood vents underneath that red area on the hood, which will also result in more air through the radiator.

I agree hood vents would be most beneficial, just throwing out spacers as a possible alternative to those who may not want vents

Reviews seem mixed with spacers

[Element Tuning]

I've had to resort to desperate measures while racing when dealing with cooling and underhood pressure. Now serious problems creep up when going 100 mph+ and on my STi pulling the rear rubber strip out did help a little (probably more at low speeds vs. high). In that application air doesn't not back flow from the windshield area into the engine like most said it should. I know this because fluids from the coolant overflow tank would spray onto the windshield. Ok there is a downside to removing that strip and one would be fluid on the windshield if the overflow coolant tank leaks a little (which it does) and two would be your fresh air vent on the passenger side would now be exposed to engine bay fumes.

Now I've also jig sawed huge holes in my hood at the track because I was getting black flagged because they thought my hood (carbon) was loose but it was just the massive pressure. After cutting the vent I noticed inreased cooling and more front end grip.

Now keep in mind this was a race application where speeds were seen over 160 mph. For the FRS/BRZ turbo guys I really think heat soak is more the real issue vs lack of airflow so if I was going to vent my hood I would do it like where an EVO hood is vented or that space between the radiator and the engine.

On my race car I have to increase airflow through the radiator at high speed as I'm overheating so I will likely cut a large opening as mentioned above, make a Gurney Flap for the leading edge, reverse Gurney forthe trailing edge, and paint some mesh to clean up the look. I did this to one of my STi hoods with god results and I'll see if I can dig up a picture.

[jamesm]

real men saw holes in their hoods.

[Element Tuning]

Well I think for street guys cutting a hole large enough so somebody could steal their turbo kit without popping the hood might not be the best choice. LOL! A good vented carbon hood or finding a louvered insert would be ideal.

My personal car......."because race car" who cares

[#87]

Does Seibon fall under "good vented carbon hood"?

[King Tut]

Probably falls closer to "vented carbon hood", but I don't know that there are any better options. I will probably buy one eventually.

[Element Tuning]

Street guys really don't need this much but real race cars do because of the high speeds and how much pressure builds up.





Air can also be dumped out the sides of the bumper or underneath the car (least ideal).

[Midtenn]

Originally Posted by DJCarbine

As long as fresh air is entering then it would still be functional, its the lack of air movement (and heat) that people are concerned about
Also the green low pressure area is right at the hood cowl it appears, so it should create a low pressure area for air from the hood to vent from. Hopefully that will also mean the possibility of more air moving past your intercooler/radiator

Best I can tell, that plot is velocity, not pressure. That means the green area is slow moving air. Forcing more air under the hood isn't going to help very little. In theory its going to induce a little more front end lift (high pressure under hood, lower pressure on top). Another side effect is that adding pressure to the engine bay is going to make it harder for the radiator to do its job since it works on pressure differential. Raise the pressure behind the radiator and it lowers the difference of pressure between the two sides and less air is going to pass through the core.

I agree that sitting still or at low speeds, it might help out some, but at high speeds, you don't want to forcing more air under the hood (pressure has to go somewhere).

[DJCarbine]

Originally Posted by Midtenn

Best I can tell, that plot is velocity, not pressure. That means the green area is slow moving air. Forcing more air under the hood isn't going to help very little. In theory its going to induce a little more front end lift (high pressure under hood, lower pressure on top). Another side effect is that adding pressure to the engine bay is going to make it harder for the radiator to do its job since it works on pressure differential. Raise the pressure behind the radiator and it lowers the difference of pressure between the two sides and less air is going to pass through the core.

I agree that sitting still or at low speeds, it might help out some, but at high speeds, you don't want to forcing more air under the hood (pressure has to go somewhere).

Makes sense. I had an issue with a vintage mustang where speeds over 75mph meant that you had little/no steering feel, and any steering input was basically ignored. The front end would actually lift due to air being trapped under the hood.... it was about as aerodynamic as a brick though.

On the composite undertray behind the aluminum skid plate there are actually vents cut into it. I wonder if thats where they want all the hot engine air to escape to, with airflow going through radiator/engine bay/and then out of those lower vents

[mid_life_crisis]

Originally Posted by Element Tuning

I'm about to cut a giant hole between the engine and radiator in my hood to extract excessive pressure in the engine bay during race conditions. It's more about allowing air to flow through the IC and radiator and then releasing that huge volume of air seen at high speeds. Given how well sealed up the bottom of the engine bay is for aerodynamics I'm seeing a lack of flow through while racing. Hood vents will allow the IC and radiator to work more effectively and you'll also end up with more front downforce.

Interesting. I was reading recently that the 2014 Corvette has the same design.

[Element Tuning]

Originally Posted by mid_life_crisis

Interesting. I was reading recently that the 2014 Corvette has the same design.

I often race with the Whelen Marsh Corvettes that run in Grand AM GT and USGT and they run a cowl type hood that vents at the windshield vs. most of the competition that vent more towards the front of the hood.

I would bet most street cars don't have vented hoods for better fuel efficiency and less drag. I was hoping I wasn't going to have to vent the hood since I don't have much front lift but the engine is just running too hot turbocharged while racing.