need OPINIONS on cutting a vent into my hood.

[leet]

That isn't going to do crap. Just like all the other holes people have carved into their hoods.

If you want it to EXTRACT air, you have to use a vent that induces a low pressure zone (IE the carbontrix hood vents). Otherwise you're just forcing more air into the engine bay (which will vent underneath the vehicle, further ruining underbody aerodynamics). Not to mention that it may interfere with cooling, as stated earlier.

 

[xveganxcowboyx]

So after looking at some of the carbontrix vents it looks like the best way to create a low pressure zone around the vent is to have a lip at the front of it so the air is forced well over the vent (kind of like the top of an airplane wing). Is this correct?

 

[xveganxcowboyx]

Dammit, double post.

Have some toast!

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[morbid_eclipse]

Have some toast!

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thats a nice piece of toast

 

[devlish]

MMmm, a little butter and cinnamin and sugar... oooh, you made me hungry. thanks!

anyways, here's my hood vent

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don't know how practical it is for perf reasons, but i like the way it looks

 

[DarkSeraph]

I'm not sure how practical it is either, but I'm sure it's better than no hood vent, and I really like the look!

 

[devlish]

that's what i was thinking... thanks!

 

[weith1111]

I'm not sure how practical it is either, but I'm sure it's better than no hood vent, and I really like the look!

If you had read the entire thread, and new a little bit about airflow, you would not "be sure it's better than no hood vent." By adding holes/openings to your hood without proper research on how it changes airflow and pressure you could do any or all of:

Prevent air from flowing through the radiator as well as it was designed or at all.
Create lift underneath the car.
Increase drag immensely.

Or a host of other things.

 

[mavisky]

FYI, for those looking to keep from overheating. I'd suggest a new radiator from Fluidyne, Griffin, or Koyo, and I just found out that Flex-a-lite is making a dual fan (slimmer than stock but not tiny) kit for our 1g dsm's.

http://www.flex-a-lite.com/auto/html/eclipse-talon-laser.html

 

[Stapl3]

I forget who's it is and where I found it. Looks fine until your eye meets the fender.

 

[Mr96GSX408]

I think it would look awesome if you did this kinda hood vent:
http://members.cox.net/stormbird/pics misc/DSC00029.JPG
http://members.cox.net/stormbird/pics misc/DSC00028.JPG
http://members.cox.net/stormbird/hood pics/Copy of 136-3668_IMG.JPG
http://members.cox.net/stormbird/hood pics/Copy of 136-3669_IMG.JPG

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Edited by mavisky : some of those pics were too big. Changed them to links instead.

 

[mavisky]

Those are just the caarbon trix hood vents, except the first one was molded in.

 

[kronix0420]

my friend, took a talon hood and cut the hump over the cam sprockets out, and put it on the passenger side of the car so it has two humps in it now, it looks uniqui, i'll try to find pics of it and post them, on a 92 tsi

 

[mavisky]

my friend, took a talon hood and cut the hump over the cam sprockets out, and put it on the passenger side of the car so it has two humps in it now, it looks uniqui, i'll try to find pics of it and post them, on a 92 tsi

Exactly what does that have to do with someone wanting to cut a vent in their hood to keep coolant temps down. For christ's sake, stay on topic rookie.

 

[kronix0420]

Exactly what does that have to do with someone wanting to cut a vent in their hood to keep coolant temps down. For christ's sake, stay on topic rookie.

sorry! he is in the process of making scoops in both of the humps, (failed to add in the last post)

 

[Zero Bar]

I think it would look awesome if you did this kinda hood vent:
http://members.cox.net/stormbird/pics misc/DSC00029.JPG
http://members.cox.net/stormbird/pics misc/DSC00028.JPG
http://members.cox.net/stormbird/hood pics/Copy of 136-3668_IMG.JPG
http://members.cox.net/stormbird/hood pics/Copy of 136-3669_IMG.JPG

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Edited by mavisky : some of those pics were too big. Changed them to links instead.

Thats exactly what I want for my car. I hate the invader hood and have been looking for a vent like that. With that, a fluidyne and some good fans it should keep the temps down.

 

[tunitallstar]

I dont know how good you are with body work, but I would definately try this on a JUNK hood

 

[igs]

That forces air under the hood, not out of it. Same as a cowl induction hood. It's all based off of air pressure principles. It's a commong mis-conception that lifting the rear of the hood lets hot air out, in fact it forces cold air in. This is good except that the air then usually exits below the car causing more turbulence and lift.

Cowl induction forces air out, not in.

As the air passes over the opening, it creates a vacuum of cold air over the windshield. This allows the hot air from inside the engine compartment to escape letting the engine breathe cooler air and therefore running stronger and longer.

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Cowl Induction Hood - How It Works
Air glides over the cowl induction hood.
It then hits the base of the windsheild, creating a low pressure area, allowing the hot air to escape from the engine compartment.

 

[igs]

I agree that cutting straight vents into hoods like this will never help in getting more cool air to the radiator. Properly designed hood vents though such as the carbontrix vent and others can be beneficial although don't expect drastic changes. Making a block off plate around the radiator opening and upgrading the radiator itself are much more effective plans. In fact the little rubber piping that is around the vents in the greyforest hood mod may actually be enough for those small openings to help get air out of the hood. A perfectly flat plane with a hole in it will always draw air into that area as you found out though.

At freeway speeds and up, there is a low pressure zone across the top of the hood. In fact, there is a low pressure zone across the entire top of the car. Cutting holes in the hood will allow the pressure above and below to equalize. This has 2 benefits:

1) Hot air will be extracted out of the engine compartment.
2) There will be less net lift on the car.

 

[mavisky]

Ok, so you clicked the first link you found in google that takes you to a vendor selling hoods for PT Cruisers.

Here's a link to a thread regarding the exact situation I was talking about. The car's discussed are C3 corvettes some of which came with a cowl induction style hood from the factory.

http://forums.corvetteforum.com/showthread.php?t=1419660&page=2

Originally Posted by Budman78
Here is something I noticed the other day on my trip.
When driving in 6th gear at 1600rpm - 1700rpm or roughly 78 mph my temp gauge reads 185 degrees. When I brought the rpms to 2000rpm or roughly 85 mph the gauge would go to 200 degrees. Do you think at 80 to 85 mph the C-3's engine bay becomes pressurized. I know there is alot of variables, but I though was interesting. My vette has all the foam inserts, stock airdam, etc. The only changes to the cooling system is electric fan which are useless at 80 mph.

It would be interesting to install a camera under the hood and watch the movement of string attached to all the parts. Are a windtunnel test.

What you describe makes sense...as your speed increases,positive pressure is building up inside your engine compartment and having a negative effect on air coming in...this issue was experienced on the original grand sports as the hoods lifted..so they compensated by adding vents in the forward area of the hood to relieve this "pressure"...in your case you are seeing it in terms of cooling air flow being restricted by this "back pressure" or positive pressure..

In fact here are some string tests from the original guy's car at speed.

Ok..My yarn test...

Test set-up...

string

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Idle {edit - fans blowing string towards window}

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55mph {edit - strings tucking inside engine bay at speed}

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at speed {edit: speedo reads around 80-90mph, string tucking closer to top shows more flow than 55mph test}

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[igs]

Cars set up for cowl induction will actually induct air. Our cars, however, are not set up like that. Our cars are like the PT Cruisers, we will expel air. We do not have engine bay side exhaust vents and sealed cowls, our engine bays build positive pressure. Post 69 in the thread you linked to helps explains the situation.

http://forums.corvetteforum.com/showpost.php?p=1555740418&postcount=69

 

[Defiant]

Nah. The base of the windshield is a high-pressure area as it tries to kick air up over the windshield. It's why air comes in through your vents when open, instead of being sucked out. The air doesn't come up in a nice upwash as shown in the PT Cruiser animation. It's all just sitting there like a solid mass, and it doesn't really want to be wedged up as the car tries to pass through it. I don't know who dreamed up that animation, but it's flawed. Surely it wasn't just someone trying to sell something.

 

[mavisky]

Cars set up for cowl induction will actually induct air. Our cars, however, are not set up like that. Our cars are like the PT Cruisers, we will expel air. We do not have engine bay side exhaust vents and sealed cowls, our engine bays build positive pressure. Post 69 in the thread you linked to helps explains the situation.

http://forums.corvetteforum.com/showpost.php?p=1555740418&postcount=69

Regardless of whether the car's setup for cowl induction or not, it doesn't change the way air interacts between two surfaces. Now he may be experiencing his heat issues because the engine bay is designed to seal up, and it's very possible that at speed with a slightly raised rear hood section that some air could spill out the sides as well, but it still doesn't change the fact that air hitting the base of the windshield will enter the engine bay when presented with a direct path.

 

[mavisky]

Nah. The base of the windshield is a high-pressure area as it tries to kick air up over the windshield. It's why air comes in through your vents when open, instead of being sucked out. The air doesn't come up in a nice upwash as shown in the PT Cruiser animation. It's all just sitting there like a solid mass, and it doesn't really want to be wedged up as the car tries to pass through it. I don't know who dreamed up that animation, but it's flawed. Surely it wasn't just someone trying to sell something.

Exactly, the air doesn't just gradually change direction and tumble around the way that animation shows. Clearly someone is trying to sell a product to a group of people who could probably care less about the aerodynamics of their vehicles in the first place.

 

[igs]

Regardless of whether the car's setup for cowl induction or not, it doesn't change the way air interacts between two surfaces. Now he may be experiencing his heat issues because the engine bay is designed to seal up, and it's very possible that at speed with a slightly raised rear hood section that some air could spill out the sides as well, but it still doesn't change the fact that air hitting the base of the windshield will enter the engine bay when presented with a direct path.

As long as the pressure in the engine bay does not exceed the pressure at the windshield base.