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Old 05-26-2008, 09:13 AM   #1 (permalink)
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Nose job for 1999 Honda CRV



When I was installing the skidplate a while back, I took a close look at the bumper.
There is pretty good air-intake in the grill above the bumper, so I'm thinking that I could close up the lower bumper holes without being hit with over-heating. (Boston area never really gets hot like Texas).
I have the SG2, so I can watch the engine coolant temperature.

I'm also thinking the plate holder might have less drag if it was lower.
(Bottom edge even with the bottom edge of bumper).?.

Since the holes in the lower bumper are shaped funny, I was thinking that a Car Bra could be used.
Since mesh screening tends to look like a solid at higher air speeds.
If the holes in the mesh were too large, it should be easy to mod them..

Here's what the mesh covering should look (somewhat) like with a full bra installed.


I'm not sure I would install the hood cover, since it would likely add drag.
Some hood covers have two small drag 'flaps' that are pushed back by the air flow, to keep the hood cover from flapping. So I would likely ditch a hood cover with the drag flaps.

I think the plus side of using mesh is, when sitting in traffic, the cooling fans would be able to suck air inside easily, since there would be almost zero surface turbulence on the mesh.. The air resistance would be small.
(and it would keep bugs out of the heat exchanger parts).


Looking for comments and ideas.

Thanks,
Rich

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Old 05-26-2008, 09:19 AM   #2 (permalink)
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I suggest going to a paint store and picking up some 3" blue painters tape. It will not damage the finish of your car and you can mask off the entire front end, temporarily to see how your temperature is affected. That way you can cut away pieces until everything is ok, leaving you with a pretty good idea of what the final mod will have to look like.
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Old 05-26-2008, 11:31 AM   #3 (permalink)
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I wasn't planing on doing any testing before hand, since I had used a full coverage bra on my old car (1991 Laser RS) for years and never saw any temperature spikes. Car bras of this type are a pretty well tested product.

I think the experimental testing part will be to determine if the surface turbulence on the mesh will make it work like a solid block at higher speeds (40 mph & up).
If there is a low pressure area behind the radiator,(due to the new skid-plate or other factors), that might negate the mesh's surface turbulence that I'm counting on..

So, I was planing on looking at the engine coolant temperatures at varying speeds. I was also thinking about placing some kind of air speed monitor inside to test the before-and-after air flow at varying speeds.

Once I had some benchmarks, I could easily insert solid blocks (sheet plastic) behind the mesh. (Making it the same as a blue tape block).
Comparing the solid block numbers to the mesh only numbers should tell me if the mesh is doing the job.
Which is, to allow air in when in stop-n-go and be aerodynamically smooth at higher speeds.
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Old 05-26-2008, 11:52 AM   #4 (permalink)
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Quote:
Originally Posted by Xringer View Post
I wasn't planing on doing any testing before hand, since I had used a full coverage bra on my old car (1991 Laser RS) for years and never saw any temperature spikes. Car bras of this type are a pretty well tested product.

I think the experimental testing part will be to determine if the surface turbulence on the mesh will make it work like a solid block at higher speeds (40 mph & up).
If there is a low pressure area behind the radiator,(due to the new skid-plate or other factors), that might negate the mesh's surface turbulence that I'm counting on..

So, I was planing on looking at the engine coolant temperatures at varying speeds. I was also thinking about placing some kind of air speed monitor inside to test the before-and-after air flow at varying speeds.

Once I had some benchmarks, I could easily insert solid blocks (sheet plastic) behind the mesh. (Making it the same as a blue tape block).
Comparing the solid block numbers to the mesh only numbers should tell me if the mesh is doing the job.
Which is, to allow air in when in stop-n-go and be aerodynamically smooth at higher speeds.
Interesting idea concerning the bra... I will be very curious to hear your results. I may go that route if indeed the numbers are favorable.

A note on radiators... I have been doing a lot of reading of late on the subject of cooling and it is my understanding that a radiator cools because of the variance between the high pressure zone in front of the radiator to the low pressure behind the radiator. If I am right (and I am sure that someone will politely correct me if I am wrong) then the real concern would be having the air pressure behind the radiator increase due to a modification, because that would increase your engine temp.
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Old 05-26-2008, 12:12 PM   #5 (permalink)
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Quote:
Originally Posted by worldskycat View Post
high pressure zone in front of the radiator to the low pressure behind the radiator
I'm trying to think of the role of the radiator fan(s) at high speeds. Wouldn't they be fighting the air pressure in this scenario? Just brainstorming, would it be beneficial to disable or (if possible) reverse the fan over certain speeds?

Blocked or not, my FWTs register upwards of 210-230F with a 192-degree thermostat. I don't have much confidence in that reading, and I haven't "boiled-over" yet...

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Old 05-26-2008, 12:34 PM   #6 (permalink)
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Since the radiator fan sits in the low pressure zone behind the radiator, when it engages it is artificially increasing the flow rate from high pressure zone to low pressure zone. Disabling the fan would work if you had a way to control the pressure values behind the radiator by some sort of mechanical channeling of air. Find a way to lower the pressure at will behind the radiator (other than a fan) and you can ditch the fan.
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Old 05-26-2008, 04:21 PM   #7 (permalink)
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I'm not 100% sure, but at higher speeds, the fans normally won't kick in because the heat sensor isn't detecting high temperatures.

But, if the grill blocking was too effective, and the temperature got too high,
the fan would be turned on. (Which is what happens when I'm stuck in slow traffic).

I think the trick is, to get the engine good and warmed up, but not extra hot.


So, if the venturi effect of air passing under the skid-plate area creates
a little low pressure around the engine, that might suck enough air through the radiator.?.

Maybe I will tape up the nose before I spent $89.95 for the Car Bra.
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Old 05-28-2008, 04:28 PM   #8 (permalink)
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CRV grille-block

When the second-generation CRX came out,Honda had abandoned the upper grille entirely and relied solely on the bumper/fascia inlet for all internal flow needs.Looking at the photo of your CRV,I'm thinking that because of the layed-back rake of the upper grille,that it probably resides in an area of lower pressure than the lower grille(which should be at the forward stagnation point for the car),and that if anything,you would want to close off the upper opening.According to rocket-scientists,a diverging, air-tight inlet duct,one radiator-height long,and one-quarter radiator-height tall,at it's opening,will provide all the air at the minimum drag.With respect to the skid-plate,the "windward" face will be at near the stagnation pressure,and once behind the "turn",under the car,the pressure will drop as a consequence of being converted from static-pressure, into velocity.
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Old 05-28-2008, 05:07 PM   #9 (permalink)
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Thanks for the input..

After taking a closer look at the upper grill, I have to agree 100%.
It's actually too high above the radiators to allow the air flow do much good.
Now I've got to figure out a way to make that protrusion smooth...


On the bottom, the two outboard holes do nothing (but add drag).
The other two small inputs (middle ones) should also be sealed over.

As you can see, there is a horizontal bar across the center of the main input.
So, I could block up the top half or the bottom half and be pretty near the recommended intake size.

I like the lower being open, since I leave the plate alone (or move it down ~2 inches).
If the upper half was open, I would want to drop the plate down about 8"..

What do you think would be better for the cd? upper or lower blocked?
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Old 05-28-2008, 06:10 PM   #10 (permalink)
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Quote:
Originally Posted by Xringer View Post
After taking a closer look at the upper grill, I have to agree 100%.
It's actually too high above the radiators to allow the air flow do much good.
Now I've got to figure out a way to make that protrusion smooth...


On the bottom, the two outboard holes do nothing (but add drag).
The other two small inputs (middle ones) should also be sealed over.

As you can see, there is a horizontal bar across the center of the main input.
So, I could block up the top half or the bottom half and be pretty near the recommended intake size.

I like the lower being open, since I leave the plate alone (or move it down ~2 inches).
If the upper half was open, I would want to drop the plate down about 8"..

What do you think would be better for the cd? upper or lower blocked?
GM,on Corvettes,Trans Ams,and some Camaros,pulled off a complete grille-block by going to a "bottom-breather" arrangement,where a chin spoiler scooped up air,and channeled it into an inlet duct to the radiator.It's an exquisite design but requires a long duct (read long nose which scrapes everything if you're not careful).You've got gobs of ground clearance and might be able to do that(which is at the cutting-edge).Without knowing how deep your radiator is,I don't know how much of the lower opening you could block without introducing cooling problems.Getting to your question about which is best,it may be a draw,as the drag reduction comes from the reduced internal flow,regardless of where the restriction occurs.With respect to form-drag,I'd favor blocking the upper portion,since the license plate is already there if it didn't curtain off the cooling air so much as to be a problem.The other thought though is that from your photo,it looks like a front airdam could do you some good,in that it would block air from under the CRV,and in that case,blocking the upper portion would make sense and the lowered license plate could be integrated into the airdam itself below the cooling inlet.Flow would separate at the lower edge of the plate,as its flat,and that sucks,however,maybe you could cheat the plate up a bit,and provide just a little radius under it for attached flow.Many thoughts! Am I thinking this thing to death! Sorry.

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