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Old 09-23-2010, 09:03 PM   #11 (permalink)
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Which is kinda along my train of thought. Block the grill off completely, leave an opening under the bumper for the air draw as needed by the radiator fan, and enjoy the MPG savings, intead of worrying about controlling the variable air flow from the front of the car.

The Honda CRX Del Sol had a very small grille opening under the bumper. What if it had no grille opening and just pulled in air as needed with the rad fan?

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I think you missed the point I was trying to make, which is that it's not rational to do either speed or fuel economy mods for economic reasons. You do it as a form of recreation, for the fun and for the challenge.
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Old 09-23-2010, 09:04 PM   #12 (permalink)
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Originally Posted by talldudenumber5 View Post
we will have to compare grill blocks once we both finish. same car, similar driving environment. let the testing begin lol
Don't forget to put your numbers in, hard to compare when there are so few entries in your log
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I think you missed the point I was trying to make, which is that it's not rational to do either speed or fuel economy mods for economic reasons. You do it as a form of recreation, for the fun and for the challenge.
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Old 09-23-2010, 10:27 PM   #13 (permalink)
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I like your questions

I did a full upper grill block, and have a lower one that can open and close as I want it . This is the best of both worlds, I can block the grill at start up or when ever I do not need the cooling. Just before the fan comes on I open the lower grill and take the aero drop instead of using the fan.
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Old 09-23-2010, 10:32 PM   #14 (permalink)
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ShadeTreeMech: An alternator is about 50% efficient, so if your fan draws 20A (275W), that's a 550W accessory load. You can use the calculator to turn it into a percentage if you like.

You definitely don't want the fan running ALL the time, because it is a pretty big draw.
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Old 09-23-2010, 10:53 PM   #15 (permalink)
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Well the aero drag for any of these solutions is the "sinking drag" which is equal to d(mV)/dt

mass (m in slugs) is the mass of air you're bringing up to speed of car (V - ft/sec) either passively or using the fan .... so you have the area (of your grill or opening) you have your speed (mph) and you have the density of the air P/RT (slug / ft^3) ... do the calc and you get in units slugs ft/sec^2 which is lbf ... that's your sinking drag required to cool engine.

So you block off the grill and let the fan suck it in (not too efficient at sucking these fans not designed for that) but it still wants the same heat transfer (mass flow) to cool the engine... but now instead of doing it passively you want to use electricity (juice) to get the job done. Not much sense in my opinion... I agree... take the aero hit instead.

The problem is not when you're cruising down the highway letting the good times roll though... the problem is when you're stuck in traffic in 100 deg heat going nowhere fast and the fan can't suck/push enough mass through the heat exchanger.

A variable area grill block seems like a good idea albeit an engineering problem... Personally I've got a permanent full upper grill block on (those are just for style mostly anyway) No discernible negative effect so far... and this winter I hope to see what a partial lower block can do...

This is one aspect the EV's definitely have going for them.
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Old 09-23-2010, 11:07 PM   #16 (permalink)
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Originally Posted by Weather Spotter View Post
I like your questions

I did a full upper grill block, and have a lower one that can open and close as I want it . This is the best of both worlds, I can block the grill at start up or when ever I do not need the cooling. Just before the fan comes on I open the lower grill and take the aero drop instead of using the fan.

Nice... is that thermostat controlled? or do you need to remember to open it... the latter not something I'd trust the wife with.
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Old 09-24-2010, 12:19 AM   #17 (permalink)
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Originally Posted by ShadeTreeMech View Post
Which is kinda along my train of thought. Block the grill off completely, leave an opening under the bumper for the air draw as needed by the radiator fan, and enjoy the MPG savings, intead of worrying about controlling the variable air flow from the front of the car.

The Honda CRX Del Sol had a very small grille opening under the bumper. What if it had no grille opening and just pulled in air as needed with the rad fan?
Well it needs some opening to pull air in. The smaller the opening, the less efficient the fan is, and you can increase fan power without pulling in much more air.
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Old 09-24-2010, 12:44 PM   #18 (permalink)
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I blocked about 75% of my grill. Also ran an LED light on the dash to see when the fan cut on. On an 80 degree day, cruising at 55, the fan will cut on for a minute every 4-5 minutes. That seems reasonable to me. Not too many days over 80 here in San Jose CA. Then last night (around 60 outside) it only came on near home when I EOC'd into a light and then restarted when light turned green. Fan came on for 30 seconds on engine restart.
I also took the snorkle off the air intake so I am pulling air from about a foot behind the radiator fan. When the radiator fan is running I can get air temps of 90-100. When the fan is off then the air temps are only 5 or 10 degrees above the outside temp. This data is making me think about at better belly pan/more sealing around hood/lights. I would like to get the air intake temps up a little more before we head into those "brutal" winters here in the bay.
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Old 09-24-2010, 12:53 PM   #19 (permalink)
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Nice... is that thermostat controlled? or do you need to remember to open it... the latter not something I'd trust the wife with.
No it is not automatic. If you want to make it wife proof, then you would need to automate it. Doax did that with his, check his thread out for how he did it.
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Old 09-24-2010, 12:57 PM   #20 (permalink)
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Quote:
Originally Posted by ShadeTreeMech View Post
Which is kinda along my train of thought. Block the grill off completely, leave an opening under the bumper for the air draw as needed by the radiator fan, and enjoy the MPG savings, intead of worrying about controlling the variable air flow from the front of the car.

The Honda CRX Del Sol had a very small grille opening under the bumper. What if it had no grille opening and just pulled in air as needed with the rad fan?
in my max i have no opening under the radiator ( under belly pan) so that would not work for me i plan to block half of both the lower openings and go from there. lol i was thinking another advantage to an upper grill block is you could paint on a grill from another company( ie BMW split grill) thought it would be funny now to convince my wife to paint it on

i really did not like the log on here to track mpg so i use a program on my wife's ipod
here are my results from may till now these are full tanks
may 13 20.8
may 24 23.8
jun 11 20.1
jun 27 21.9
jul 7 22.6
jul 29 21.8
aug 13 23.3 ( started hypermiling practice again)
aug 23 30.4 (upper grill block and mud flap deletes, mostly highway)
aug 25 24.9 (back to the city)
sep9 27.1 (461 miles ,half tank in branson, half tank highway)

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