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Old 02-27-2010, 11:20 PM   #21 (permalink)
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Oh, i don't doubt its strength at all..... it felt very strong when i saw it in lowes. And i could probably bend it with some pipe benders my dad has (hes a plumber).

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Old 02-28-2010, 01:40 AM   #22 (permalink)
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gascort -

I haven't even noticed this thread until today!

I'm impressed with your work, albeit quick, fast, and somewhat clean.

I do have a suggestion about your cooling issue, though - Even though your (several) round ducts had the same surface area as your square duct, they would not have had:
1 - the same volume
2 - the same inlet/outlet velocity.

You changed two key features by adding several round ducts instead of a single square duct, in that the surface area remained similar, but you added much more non-flow area because of the increased number of surfaces the flow has to contend with.

In fluid dynamics, the fluid moving through an object nearly (with caveats) matches the fluid movement around an object. That is to say - there is still a turbulent boundary layer, and skin associated drag, etc.

More tubes of a smaller type would increase skin drag of the fluid movement through them, which explains why (even though the surface area was the same) you overheated with the duct work you used.

Second effect - the length of the ductwork creates an increasingly thick boundary layer up to a given point. A cylinder which is open to airflow at one end, and restricted at the other, is actually more like a directed nozzle, although less dramatic.

IOW - You weren't getting the flow you needed.

Adding back the square unit you had of the same dimensions may be the best idea, as well as sealing your radiator to the core support and ensuring that your flow through the radiator isn't disrupted by something in the flow path, such as grille elements.

If there needs to be a grille screen, it should normally be at the absolute surface of the extension you're working on, with tapered ductwork of increasing area per depth.

The overheating you were experiencing was also most likely accompanied by hot and cold spots in the radiator. If you had a surface temperature thermometer (IR touchless type) you could quickly see that there would be pinpointed spots where your duct work opened to the radiator that were cooler than the rest of the surface. Those points clearly were not enough to cool the flow sufficiently.
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Old 02-28-2010, 12:23 PM   #23 (permalink)
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Christ, thanks for the fluid dynamics insight and background; I was worried about lower flow in the pipes from the start; longer than my old duct was to start with, plus smaller area for each, slightly curved, and to top it all off, it's bumpy on the inside! Likely what the air saw at 70 mph was four 1 inch pipes.
Luckily my commute isn't enough to get the car hot with our cold temps lately. Will have to fix before driving a longer distance or before outdoor temps increase, and I think the square duct will be just fine. Just need to engineer a door to open/close.
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Old 03-01-2010, 12:05 AM   #24 (permalink)
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So I'm getting really inspired by this. Is there a reason to make it angled to push all the air over the car, as opposed to merely around the sides of the car?
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Old 03-02-2010, 10:00 PM   #25 (permalink)
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My thinking is that the top of my car is probably the cleanest shape and cleanest at the back end with my Kammback. The front wheels don't have skirts on them so that is an aero. rough area. If I had wheel skirts on all wheels, I think it would be better to push to the sides than the top; less distance to push the air. Just my thinking, not sure if it's right.
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Old 03-04-2010, 01:11 AM   #26 (permalink)
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nice fab work!
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Old 05-26-2010, 01:48 AM   #27 (permalink)
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Nice post...

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