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Old 09-04-2012, 02:49 PM   #11 (permalink)
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I doubt that putting the block behind the grillwork would make a big aero difference, for the following:

The front grill on an auto is at--or very near to--the stagnation point on the nose. Thus, the flow velocity near the vehicle is zero, or very close to that.

What happens is that the air upstream of the car "senses" the blockage...and the vast majority of the air flows AROUND the obstruction. This is true of all sub-mach flow. (Sometime look at the "grease streaks" you see on aircraft rivets...the airflow on the fuselage just ahead of the wing has a pronounced upward flow component, as the air tries to fill the low-pressure are on the top of the wing.)

So, keep it under 720 MPH, and it makes little difference. Above that, you want knife-edge leading edges anyways.

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Old 09-05-2012, 08:57 AM   #12 (permalink)
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I'm not sure your cause and effect follow each other.

Correct that the grille is near the stagnation point. (more on some cars than others) A rear block will cause air to "pile up" in the blocked cavities. The rest of the air will flow mostly smoothly over those pockets of air. A rear block should work nearly as well as a smooth outer block.

You do have to get past that pesky problem of the air pushing it in and then leaking around the block. A front block doesn't have the problem.

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Old 09-17-2012, 07:10 PM   #13 (permalink)
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Originally Posted by darcane View Post
I had one on my truck inside the grill. The way I had it mounted, it would flex and allow air to flow past it and wasn't very effective. I noticed an improvement by moving to the front of my grill.

I think if you mount behind the grill, you need to make sure it will still prevent air from flowing around the block once the vehicle is moving.

Mounting in front of the grill makes this easy, since air pressure will keep the block in place.
Cool just fabricate it so you get just enough air,, thanks
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Old 09-17-2012, 10:42 PM   #14 (permalink)
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see the grill block thread in my signature on a plexiglass front block
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Old 09-18-2012, 01:29 PM   #15 (permalink)
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It depends on the vehicle if air can go around a behind the grill block. On my grandprix I used plexy for picture fraims and cut it to the grill insert installed and the air presses it tighter. The same is true for my Golf as the grill sits against a support and the air tightens the seal.
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Old 09-24-2012, 08:52 PM   #16 (permalink)
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I have an inner block behind my grill which is only about 1/2in deep but I took the grill off used coroplast, black just like the grill. Then used Gorilla duct tape on the edges and it seals perfectly.

Now it's getting time for the lower block soon!


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