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I had no idea what forum to post this in because it fits a lot of categories. I am modifying my from grill area to help with cooling and aerodynamics , which will affect the engine also. It’s kind of bodywork too , and some fab and welding . 
Anywho- here’s some pics of the start of the project . Making use of a huge box that my lawnmower came in to mock up .

Goal is make this aerodynamic gain by blocking the air from getting in all the wrong places. Also getting air in the right places for cooling and better engine-temp control. 
At 75mph cruise I get some buffeting on the front end . I can see the hood doing a little shaking from the air getting under it . 
And if I get it looking clean I think it will good. Not really a sheet metal guy , but I can bend some aluminum around . I’ve been practicing with my TIG . I suck , but I’m hoping I can make some welds look pretty with some sandpaper-lol. 

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Edited by madkaw
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8 hours ago, Ben280 said:

It's important when ducting the radiator like this to make sure you blank off the sides as well, such that the only place for air to go when it gets to the front of the car is through the radiator. 

Yep - I’m getting there . This is just the early stages of the project . 

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1 hour ago, JMortensen said:

Can't really see what you're doing on the bottom, but also blocking off the entire area between the front valance and the rad support helps to minimize air that goes through the grill and then down under the car. I expect you're aware of this already.

I’m only half done . The front grill area will be completely blocked off except a small opening in the radiator box . 

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Just a tip from the Z-cars that race competitively: you want to block air from going anywhere other than the rad, oil cooler, fresh-air ducts (if you are still using them), and either an engine-air intake or allow cool air to blow through to the engine bay on the drivers side. 
 

From a weight management perspective, this means forcing the cladding you are proposing to the extremes. As in, take the concept of creating a front-facing shroud as you proposed but block ALL air from moving over  (between the hood and the rad support), under (between lower rad support and your air dam/valance) and sides. 
 

the front orifice on an S30 is bigger than necessary so a lightweight bumper actually aids in aero by blocking and directing some air away from the orifice. 
 

attached is an example of Greg Ira’s car as an example.

 

all this to say, your idea is not bad but not optimal (if you care). If you do insist on keeping it narrow, I would put a slight angle inward on the sides. Sounds counterintuitive, but this creates a Venturi effect at slower speeds which will actually increase velocity into your rad. Angling outward will cause an eddy current on the sides of the rad support creating drag. Keeping a neutral angle (as you drew) will cause a thin surface to “flap” due to turbulent air flow at speed. 
 

just some thoughts! 

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Not sure I understand what you are saying. The grill opening will be completely blocked off except a small opening for the radiator . I will shooting to keep air from escaping anywhere around the fascia . 
 

 

 

all this to say, your idea is not bad but not optimal (if you care). If you do insist on keeping it narrow, I would put a slight angle inward on the sides. Sounds counterintuitive, but this creates a Venturi effect at slower speeds which will actually increase velocity into your rad. Angling outward will cause an eddy current on the sides of the rad support creating drag. Keeping a neutral angle (as you drew) will cause a thin surface to “flap” due to turbulent air flow at speed. 

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@madkaw oh I see! So the opening to the radiator is the only place air is going past the front fascia. Understood. Now I get what you are doing. You will be reducing the total size of the front-end orifice. If you do want to optimize for drag, you can still make the front-end opening narrower than the surface area of the radiator. It looks like the way you have it now has the orifice size matching the rad surface area which isn’t bad, you just don’t need it that big if you are trying to reduce drag. 
 

@calZ yes, going from a smaller opening expanding to a slightly larger surface area for the rad is a common strategy for minimizing drag but still getting good flow through the radiator. You see this on race cars, but also modern performance cars. Few that I have first hand experience on is a Z31 and Z32. The large opening we have on the front of an S30 creates more drag than the amount of opening we need for air to get to the rad etc. G-nose is one example of the front-end optimized. Any loss in airflow at lower speeds/stopped is made-up for with a fan on the back-side of the rad. 
 

these are all just generalizations, so I can share some photos and a pic from a book as examples if it helps.

 

 

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9 hours ago, AydinZ71 said:

yes, going from a smaller opening expanding to a slightly larger surface area for the rad is a common strategy for minimizing drag but still getting good flow through the radiator. You see this on race cars, but also modern performance cars. Few that I have first hand experience on is a Z31 and Z32. The large opening we have on the front of an S30 creates more drag than the amount of opening we need for air to get to the rad etc. G-nose is one example of the front-end optimized. Any loss in airflow at lower speeds/stopped is made-up for with a fan on the back-side of the rad. 

 

Now that I will agree with. You don't need all the capture area, and angling the ducting to act as a diffuser and increase pressure at the expense of velocity is good for the radiator.

 

It doesn't match your statement that the angling would create a venturi effect and increase airflow at low speeds, though.

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20 hours ago, calZ said:

 

Now that I will agree with. You don't need all the capture area, and angling the ducting to act as a diffuser and increase pressure at the expense of velocity is good for the radiator.

 

It doesn't match your statement that the angling would create a venturi effect and increase airflow at low speeds, though.

 

You know, I could be completely wrong on the venturi effect. Its just my opinion, but I don't have any data to support this. I have experienced this in mechanical lab, but never put any sensors etc. on a car. 

 

You said it, diffuser :) . I think the effect may be more complicated than I am giving it credit for. It actually is REDUCING the velocity by expanding the surface area with a consistent flowrate. If the velocity drops down to linear flow vs. turbulent flow, maybe that is the ticket? Anyhooo, I gladly concede :)

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Made more progress on the fascia . I think my templates will help me think this out as far as sealing edges and the getting the best look . More than likely the grill won’t go back on. I think I want to bring the top of the fascia out a little , but not much . I need to cut a hole for my breather pipe . Need to find a place for the horns . I don’t plan on having any real framework since I will be using .125 sheet to fab everything . 

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