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Old 07-04-2010, 08:39 PM   #1 (permalink)
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Grill Block Summary

Have read alot of the threads on Grill Blocks. Does the following Summary of Grill Block Priorities sound right? (I'm going on memory here.)

1. If you have 2 grills, Block the upper first. This will generally cause you to induct slightly hotter air in the summer as it is closer to the road. However it will keep the blocked air rising over the vehicle undisturbed. For the same reason, if you have a single grill, block from the top, not the bottom.

2. Block from the sides inward instead of from the center outward so that blocked air flowing around the sides of the vehicle is undisturbed.

3. Duct the air from the remaining opening to the radiator. (Should this duct be wider at the radiator than at the grill, narrower, or the same size???) If you don't duct the air from the grill, at least seal the opening between the grill and the radiatior so that you get the best bang for the buck from the air you do allow to enter by not letting it escape before it goes thru the radiator.

4. If you are able to, duct the air from the back of the radiator out of the engine compartment via shallow openings in the hood not far from the front of the hood. Failing that, duct it out the wheel wells or sides of the vehicle.

5. Some cars may not need any opening in cool climates.

6. To determine the size of the opening, attach a wire to the fan or fan relay and route it back to a light in you can see. Determine how often your fan comes on w/o the grill block and with the grill block under similar conditions. The idea is to not have your fan cycling on much more than with no grill block. A 12 volt bulb or an led with about a 550 Ohm resistor wired in series with it will both work - but the 12 volt bulb will be of higher wattage and will get hot.

7. In the process of creating your grill block, you may also be able to, with little extra effort, create a more streamlined front end that better directs air over and/or around the sides of your vehicle. For example on my Subie, the front bumper protrudes out further than the upper grill. So I plan to slope the grill block from the top of the front bumper to the top of the upper grill opening.


Last edited by 4536; 07-04-2010 at 08:46 PM.. Reason: spelling, clarification
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Old 07-07-2010, 02:56 AM   #2 (permalink)
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I can't say how accurate any of this is, being that I'm a total n00b, but my MINI has a functional hood scoop, which tells me I can probably block both the upper and lower grilles without messing with the car's cooling too much. I have makeshift grille blocks in place right now, and I took the car for a spirited drive today to see if the temp. indicator threw me any red flags, but I saw no problems. Any thoughts on whether or not to expect problems later?
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Old 07-07-2010, 01:36 PM   #3 (permalink)
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Do you have a real temperature gauge? The factory one in the dash is useless.

With my Scangauge, I can see exactly what the water temperature is. Knowing that the cooling fan comes on at 206F, I try to keep max temp somewhere around 200. If it starts hitting the fan regularly, I open up the radiator a bit more. For a temporary fix, run the heater for a bit, as a secondary radiator.
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Old 07-07-2010, 01:38 PM   #4 (permalink)
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To the first post - Good summary.

Point 3 - You want the grille opening to be smaller than the radiator. The radiator is a restriction, so less air can flow through it. A smaller grille opening will still flow as much air as the radiator can handle.
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Old 07-07-2010, 03:27 PM   #5 (permalink)
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Quote:
1. If you have 2 grills, Block the upper first. This will generally cause you to induct slightly hotter air in the summer as it is closer to the road. However it will keep the blocked air rising over the vehicle undisturbed. For the same reason, if you have a single grill, block from the top, not the bottom.
How is the upper grille closer to the ground?

Quote:
I can't say how accurate any of this is, being that I'm a total n00b, but my MINI has a functional hood scoop, which tells me I can probably block both the upper and lower grilles without messing with the car's cooling too much. I have makeshift grille blocks in place right now, and I took the car for a spirited drive today to see if the temp. indicator threw me any red flags, but I saw no problems. Any thoughts on whether or not to expect problems later?
I can't speak for the supercharged Mini, but the Turbo used the hood scoop for the intercooler, if I recall right. I'd be leary about blocking it.
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Old 07-07-2010, 04:10 PM   #6 (permalink)
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Quote:
Originally Posted by texanidiot25 View Post
How is the upper grille closer to the ground?
The way I understood it was that you'd be intaking warmer air because the air was closer to the hot pavement - not the opening.

That's my guess.

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Old 07-07-2010, 05:17 PM   #7 (permalink)
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i'm not 100% sure of this but from my experience so far i'd say if you have to leave an opening, make a slim horizontal one. or several with a bigger distance in between than the height of the opening.

this is good, because at low speed one can have the required opening, but at speed the slim opening will "plug up" and the grill will appear as a solid form to the air
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Old 07-07-2010, 06:31 PM   #8 (permalink)
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stickys

You might want to re-visit Sticky#4,mod-data #9.It dedicated to internal drag,with many contributions from members.
Personally,I would be reluctant to make any general claims or recommendations and I would look at every vehicle on a case-specific basis,especially Dodge trucks,with their parallel vs serial cooling/AC heat exchangers.
I think Korff is the one to follow,all NASCAR teams use his stuff,at least on the inlet side.

Last edited by aerohead; 07-07-2010 at 06:33 PM.. Reason: missed word addition
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Old 07-07-2010, 06:35 PM   #9 (permalink)
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Unfortunately, this is one mod I could never try safely with my Jeep. It would get way too hot with the 360 under the hood. They had to change the grille design and add heat extractor vents just to keep it cool with the bigger engine.

In the 102* weather yesterday, it was running about 205* on the highway at 60mph, and just under 210* around town (e-fan on low due to A/C system pressure). It hit 210* a couple times driving up hills in town. I wouldn't want to reduce airflow in this thing, at least not in the summer.
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Old 07-08-2010, 04:41 AM   #10 (permalink)
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some carmakers like bmw are using automatic grillblocks that open/close depending on cooling requirements.

for cars where a full or even partly grillblock can cause overheating can be a problem with the grillblock a manual or automatic variable grillblock might be interesting.

using the electric fan signal as a trigger should give you a fairly good indication when things need to open.

cooling can also be improved by using hood vents abouth halfway the length of the hood just ahead of the windshield stagnation bubble. as hot air rises these will even aid cooling when the car is stationary.

than again if a grillblock is not an option, it means the designers did a good job of giving it the right size for the engine and it's as efficient as they could make it.

manually installing a grillblock in winter is also a good practice, cars like the old citroŽn 2cv used to have a factory supplied, grille sleeve with just a few tiny openings to block the grille in winter, but even a piece of carboard in the coldest days is something.

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