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Old 04-13-2012, 09:04 PM   #11 (permalink)
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Quote:
Originally Posted by Cd View Post
Call me crazy, but I like the look of your duct tape mod.
I'm sure it looks worse in person, but from the picture ( on my smartphone - no wonder eh ? ) it is hardly noticeable since you used white tape.
The grille looks much better plugged up like that to an aero trained eye.

Looking forward to your progress !
Thanks, ya its actually not too back. You can tell, but most people dont even notice the grill, just the skirts. The fiberglass will be more obvious since that will include full skirts, but I'm not worried what people think of the looks. The thing definately coasts better, and the kick panel noise is gone. Hopefully with the bottom sealed up, I can use less deadening as well, allowing me to strengthen other parts of the build more.

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Old 04-13-2012, 09:07 PM   #12 (permalink)
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You post with lightning speed ! I just edited my previous post.
( I have a bad habit of editing post )
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Old 04-13-2012, 09:11 PM   #13 (permalink)
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And everyone on the site says in one voice " You are going to tuft test the car right ? "
We all love tuft tests on this site.
It's the ultimate nerd porn.

Seriously, if you tuft test the car please share your results !
Tuft testing on your car will show the problem areas you have to work on .
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Old 04-13-2012, 09:24 PM   #14 (permalink)
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Tuft tests will eventually be done once the weather is more up to it.

Depending on the weather this weekend, I may block more and more of the grill to see how far I can go. The upper grill can go for sure, but I'm curious about the air that goes in under the bumper.
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Old 04-14-2012, 01:18 PM   #15 (permalink)
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Quote:
Originally Posted by TOOSTUBBORN2FAIL View Post
Thanks mort, that was my thought, if ones going to the back, I didnt think it made sense to keep the drag from the radator at the front and then add another heat exchanger in the rear, even if it just breaks even. I cant help but think I'll get a little something though, using the cars wake to pull the air through.

Just curious, your saying that from the inlet to the outlet, there should be a 15 degree difference in temps? I could probably do a rough test of that pretty easily.
Hi TOOSTUBBORN2FAIL,
The 15F air temp differential is just an educated guess. If you can think of a way to measure the air temp. in the radiator outlet flow, maybe 5 different spots averaged, then you'd know.
There isn't really much vacuum behind the car. Imagine the back of the car is just the trunk lid height and width, say 7.5 sq ft, and the total aero drag force on the car is about 90 lbs (at 65 mph). If all the aero is suction in the wake on just that tail part, that's about 0.08 psi. So you build your radiator to fill the back of the trunk and the air is sucked through, that air comes from somewhere, duct work from under the car? Is that air at a high enough pressure to push 10000 cfm through the radiator? I think you need a fan.
However, this is a good idea. If you can insert air into the wake volume, using a few hp fan, and remove the radiator from the front of the car then there should be some reduction in aerodynamic drag.

You compared removing the radiator opening with the flat license plate. The license is smaller, but if it is centered it adds almost 0 to the cd. Somewhere on the front of any blunt object is a small flat area, and it can be quite a large percent of the frontal area before it makes much difference. Also the standard cd for a flat plate, considering it is on the front of a long object is 1.0. The opening for the radiator is a different problem. The radiator dumps heat by causing the air to be turbulent as it passes through. Basically radiators have the worst cd of anything on purpose. So the cd for a radiator opening maybe 2 or 3. Modern cars reduce the drag due to having to have a radiator by using slat vent like openings and setting the radiator at the back of a plenum, then suck air through with a fan when needed. It helps, but the biggest single contributor to drag at the front of the car is still the radiator.
-mort
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Old 04-14-2012, 01:32 PM   #16 (permalink)
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enough/sense

Quote:
Originally Posted by TOOSTUBBORN2FAIL View Post
I was wondering how much benefit it would actually be, considering the fact that the front bumper still needs a flat portion for the license plate to go back on. The other thing I was wondering was if the radiator in the rear would have enough cooling capacity at low speeds or idle.

Heres another question. If the radiator stayed in the front with a much smaller and ducted grill, does it make any sense to move the condensor to the rear, knowing that the HVAC box is going to be in the trunk no matter what? Or should it just stay in the front, and keep the rear of the undertray closed?
The electric fans would cover the periods of idling and low speed operation so that part is covered.
If you do the Walter Korff full-width,1/6th height opening,airtight inlet duct you'll have the drag minimum for the inlet side of the cooling system.
Obviously,if you maintain the original condenser location,then you've saved some work,except for the tubing extensions to the rear.
If you went ahead and did the trunk-mounted heat-exchanger,you could try and mimic a trick Ferrarri has done with their 599XX racer.This car has a porous belly pan diffuser in which two trunk-mounted electric fans scavenge air from,then blast out to the wake area in the locations vacated by the tailights.They claim that by pulsing the jet,that the wake can be momentarily detached from the car.
They make no drag benefit or speed claims,but the idea is tasty.It has been known for decades that a suction slot at the back of a car can beneficially alter the flow for reduced drag.
You might want to look at that Ferrarri.
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Old 04-14-2012, 11:04 PM   #17 (permalink)
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Unfortunately there isnt any room for anything in the trunk, it would need to be under the car, and vented through the rear bumper. Hence the need for a thicker but smaller rad and condensor. It would need to be custom.

I'm familiar with the ferarri, I have multiple pics of it on the computer. I'll look up Walter Korff. Anything I do, front or rear, would be fully ducted as smooth as possible with fiberglass. Gives me practice that I need, since the dash, center console, and rear seat area are being rebuilt out of fiberglass, as well as the front and rear bumpers, and wheel skirts.

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