I am still thinking about changing the hood design. ACtually this has been on my mind for years, and I just cannot seem to get a handle on what I want to do. These are the concerns:

1. Looks. It has to look good. I know all abut that eye of the beholder thing.
2. Cooling, It must improve cooling in some way.
3. Protection from rain fall. Not that I drive this car i the rain much anymore.

As far as cooling goes, there are two ideas at work. One is to have an opening that allows warm air to escape the under hood area, which does not also increase the under hood air pressure in the way a forward facing scoop does, and the other is to decrease the under hood pressure to increase the pressure differential between frontal area of the radiator and the under hood air pressure. If you read about this, you will find that auto designers place a manometer in front of the radiator, and under the hood in the wind tunnel to find how how scoops, and vents and such effect this. If the pressure under the hood goes up too much, then the radiator becomes less effective. And, forward facing hood scoops absolutely raise the under-the-hood air pressure. That is why I am thinking my forward facing hood scoops, while they look cool do more harm than good.

So, if you just cut a hole in the hood to allow air out, then you also allow rain in, and this must be dealt with. There must be some sort of baffle and gutter system, such as the turbo K cars had. And to further complicate things, there is a low pressure area right in front of the windshield. I am wondering how far out into the hood this extends.

Several of the newer Mercedes models including the cute little SLK have a vent which looks very much like a standard cowl vent but it is located about 6" out into the hood in front of and parallel to the windshield. I am wondering if this allows air and heat out, or if it is bringing in cool air as a result of being in that low pressure area in front of the windshield.

In looking at the stock '69 GT hood, it looks like the bubble that runs down each side of the hood could work effectively to release trapped heat without raising under hood air pressure. If I could get one cheaply enough I might just work with that. However, it is also possible to pattern a custom design after the stock design.

Those wide but shallow scoops that Subaru has used to get air into their intercoolers are now popular. If you turned this design sideways, it might allow the warm air out without raising the under hood air pressure.

Any thoughts out there? I love that fact that folks on this forum, will have opinions, and offer them, on such topics. Thanks in advance.

For the record, this plastic hood is beginning to crack around the hood scoops. I am no longer feeling attached to it, or the design.

Sam

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Hmmm. That's a tough one Sam.

The problem is that MOPAR guys are purists. If it wasn't on that car from the factory or documented through a dealer's bill of sale, it shouldn't be there.

Personally, I like your twin scoop hood, but I know you are trying to cool things off under the hood. Going to have to think about this one for a while.

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Chris'
Autobody
Restoration
Service

Actually, there's a high pressure area just in front of the windshield.................

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Looking forward to talking this weekend in person...

Lou

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Home of Slant6-powered fun machines since 1988

So how does this effect the situation? Does this mean an opening there will not release heat? Does it mean an opening there will draw in air, and thus increase the under hood air pressure level? Don't want that. Do you think the mercedes vents are for letting heat out, or air in? Look at the SLK.

The more I think about this, the more I like the idea of a stock GT hood with the bulges opened up somehow. They must be pretty hard to find these days.

Sam

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I think maybe you like this hood because it looks much like the stock 340 hood on the Darts and Demons from 70 - maybe 72. They are cool, but don't help my situation.

To fill you in a bit, I have ordered a new electric cooling fan that has been back ordered for months. Did I mention this? It is a mere 3 1/4" deep, and includes a full shroud. That should help a lot. But the manufacturer says the motors are back ordered, and hard to get. I would guess so, since I have never seen a motor for a 16" fan that was this thin. I am eager to see it get here and installed. It should improve cooling.

Sam

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Part 1:

http://www.autospeed.com/cms/A_2159/article.html


Part 2:

http://www.autospeed.com/cms/A_2160/article.html


Part 3:

http://www.autospeed.com/cms/A_2162/article.html

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

I have admitted this before (hide under table), but for 90% of my life I have been a GM guy. You can't beat a cowl induction hood. I have had them on Mopars, Fords, and of course my GMs. I even have a friend that has one on his Mirada. It works, simple, and cheap.

Just saying..........

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Chris'
Autobody
Restoration
Service

I am far from an engineer, but the high pressure area, when attached to the carb (or any air intake) cools the inlet air. Notice how your cowl vents work. That is better than A/C any day. (works even better with the a/c on though (
)

There has to be another means to release your hot air

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Chris'
Autobody
Restoration
Service

The induction on my car flows from under the fender into a filter box lifted from a Cadillac at a junk yard. I had to move the battery to the trunk, and it sits right where the stock battery sat. This works well, and the induction air is about as cool as it could get. My desire is to release under hood heat, and reduce under hood air pressure to create better flow through the radiator, and thus better heat transfer there as well.

What kind of hood design will do this is the question. I have already put the fender vents in, and they work. But the present scoops actually work against the goal now.

Sam

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I'm not sure why you have a concern with underhood heat and air pressure. Unless you've sealed the bottom of your engine compartment, pressure build-up under the hood should be minimal. As for the heat, without any flow restriction after the radiator, your rad should have no problems with airflow through the core. You've also ducted cool air to the air cleaner, which negates the need for a cool engine compartment.

If you don't like your current hood, I would go with a flat (scoopless) hood for better aerodynamics.

Install an oil cooler

Can you get one? I have a manometer on my paint booth to tell me when the filters are clogged. I don't think it cost much (mine was part of the booth package).

I am guessing that if you took your current hood to a wind tunnel (ya, I know... will never happen) you will find that those scoops do nothing. They are simply back too far and down too low to allow air to be forced in. Think NHRA Pro Stock or Pro Modified type cars. The scoops are up to the roof of the car to get air.

My thoughts are that designers (at least for common autos) add vents and (in the past) scoops for style. You are going to have to look at very exotic cars and maybe even bikes (if not the space shuttle) to find vents that reduce pressure and cool.

The oil cooler is a good idea, but given your radiator and inter-cooler you may not have anymore room in that area.

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Chris'
Autobody
Restoration
Service

The turbo puts out enormous heat. That is one reason the hood is cracking. I think there is just a ton of expansion and contraction with the plastic. When I designed this hood, there was no turbo.

Sam

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I own a piano restoration shop which does refinishing as part of the restoration. We have a manometer which I can easily borrow. I will do that. The web sites that discuss this kind of thing on a regular basis suggest using a manometer to check out what the air pressure is in front of the radiator, and under the hood, and I would think you could find out where the high pressure areas are above the hood.

I am pretty sure the vents in the top of the turbo K cars were there for a reason beyond style. The look well thought out.

Sam

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