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Old 08-30-2012, 02:57 PM   #1 (permalink)
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Hidden grill block in the back of the grill, usefull or useless?


grill blocks are very useful to get a higher mpg, but the look of these blocks lokks horrible to me.

Now i got an idea.

The german Opel Calibra was built with several different engines, but its body was always the same. The slowest engine (115hp) as a integrated upper grill block, hidden behind the grill. So it looks like normal, but ther cant get any air trough.

This smaller engined Calibra hat an cw of 0.26, all other engined Calibras had cw 0.28 to 0.29.

I´have no information if this car was sold in the usa, but you will find several pictures with google. Its upper grill goes deep in his front-bumper, so with a block at his end there is a deep hole. Does the air built a "filling" so that there are no turbulences, or is it a very bad aerodynamic idea?

Kind regards,


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Old 08-30-2012, 03:07 PM   #2 (permalink)
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Its alright, but not as good as an outer grill block.

IMO if you're that stuck on looks make a nice looking grill block yourself. There are a few examples on the forum.


It takes more time and cost more, but you're the picky one.
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Old 08-30-2012, 03:14 PM   #3 (permalink)
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it will help with warm up times and depending where your intake gets cool air it could help keep cool air away from the intake making it a bit warmer. It will not have the aerodynamic gains from an external block though

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Old 08-30-2012, 03:28 PM   #4 (permalink)
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I have tried both in front of and on the back of the grill, there was no measurable difference between the two on the 2009 Corolla. It may be dependant the properties of the grill so your results may be different. However on the 2012 Ford Focus, Fiesta and other cars, they have active grill shutters and fake grill openings etc that all use the "in the back of the grill" construction. If it made a large enough of a difference they wouldn't have bothered to make it look the way they did.

I have mine behind the grill.
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Old 08-30-2012, 04:00 PM   #5 (permalink)
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How about a piece of clear plastic in front of the grille? It's almost invisible, and has more aero advantage. In some cases the plastic may be black or in the chassis' color and still be barely visible.
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Old 08-30-2012, 04:30 PM   #6 (permalink)
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I have a plexiglass block on my upper grille. It's visible, but not in your face.

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Old 08-30-2012, 05:08 PM   #7 (permalink)
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Originally Posted by Gealii View Post
It will not have the aerodynamic gains from an external block though
It will still help.

The flow may not be quite a smooth as a well made external block, but it's still better, aerodynamically, than no block at all.
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Old 08-30-2012, 05:39 PM   #8 (permalink)
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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.
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Old 09-01-2012, 03:14 AM   #9 (permalink)
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Originally Posted by Gealii View Post
It will not have the aerodynamic gains from an external block though
I mostly disagree. "Buckets" in the front don't hurt aero much if at all.

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Old 09-02-2012, 09:18 PM   #10 (permalink)
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I had the same experience as Darcane that the behind the grill block would flex at higher speeds and open up a little, leaking air. So it wasn't quite as good as my present external grill block. But it does help.

I also used clear plexiglass for the behind the grill block, so it was really invisible.

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