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Old 06-24-2008, 10:52 AM
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How to exhaust engine compartment heat?

I have a very tight engine compartment, and am looking for ways to exhaust some of the hot air at hwy speed. Car seems to be ok during city driving, but can begin to climb temp wise on the hwy. I figure it is an airflow problem.
I remember reading about “draft tubes” somewhere (not the PCV type) and was wondering if there is any information on them. I have Googled, but come up with engine crankcase breather type tubes.
These are more along the lines of 3” tubes that hang down below the engine compartment and sit in the airflow below the car. The air flowing over the tube cause negative pressure inside the tube, and that helps to suck the air out of the engine compartment. I'm wondering if there is an optimum reverse angle to cut them at to get the maximum effect ? It's kinda like the airfoil leading edge thing.

BTW. I'm running a Ford Taurus 2 spd fan and I have made my hood lovers fully functional, and am sitting on the fence on whether removing the cowl weather strip is helping or hindering. (helps in city traffic, hwy ???)




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Paul

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Old 06-24-2008, 11:13 AM
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engine heat.......

HI,why not use the same thing that pontiac and camaros have used for years, its a piece of rubber(bumper material type) that hangs straight down just forward of the radiator. my elec fan went out 1oo miles from home,and i drove my 87 firebird home (on the freeway) without overheating.
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Old 06-24-2008, 11:13 AM
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cowl hood would help
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Old 06-24-2008, 11:43 AM
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Quote:
Originally Posted by boatbob2
HI,why not use the same thing that pontiac and camaros have used for years, its a piece of rubber(bumper material type) that hangs straight down just forward of the radiator. my elec fan went out 1oo miles from home,and i drove my 87 firebird home (on the freeway) without overheating.
I would like to but my intercooler scoop sits there :-(

dawg
Want to keep the car sleeper looking. Cowl hood would be letting the cat out of the bag. ;-)
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Old 06-24-2008, 12:29 PM
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Wrap the exhaust... might help some
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Old 06-24-2008, 02:03 PM
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Since your hood hinges at the front, just lay the hood down without latching it so that the trailing edge sits up above the cowl. Make a highway run with it and see what happens. That will be an easy and no cost way to tell if expelling some of the underhood air in this manner will help.
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Old 06-24-2008, 03:26 PM
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Quote:
Originally Posted by techinspector1
Since your hood hinges at the front, just lay the hood down without latching it so that the trailing edge sits up above the cowl. Make a highway run with it and see what happens. That will be an easy and no cost way to tell if expelling some of the underhood air in this manner will help.
I have tried that by accident, and the hood starts to lift up. I don't know if it is being pulled up by the low psi area neat the cowl, or if it is the exhaust air being forced out of the engine compartment. I don't know if I would want to drive like that unless I had some sort of safety latch.
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Old 06-24-2008, 07:41 PM
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Use some good strong wire to limit the lift and go for it.
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Old 06-24-2008, 08:15 PM
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Quote:
Originally Posted by quick72toy
I have a very tight engine compartment, and am looking for ways to exhaust some of the hot air at hwy speed. Car seems to be ok during city driving, but can begin to climb temp wise on the hwy. I figure it is an airflow problem.
I remember reading about ?draft tubes? somewhere (not the PCV type) and was wondering if there is any information on them. I have Googled, but come up with engine crankcase breather type tubes.
These are more along the lines of 3? tubes that hang down below the engine compartment and sit in the airflow below the car. The air flowing over the tube cause negative pressure inside the tube, and that helps to suck the air out of the engine compartment. I'm wondering if there is an optimum reverse angle to cut them at to get the maximum effect ? It's kinda like the airfoil leading edge thing.

BTW. I'm running a Ford Taurus 2 spd fan and I have made my hood lovers fully functional, and am sitting on the fence on whether removing the cowl weather strip is helping or hindering. (helps in city traffic, hwy ???)




Thanks
Paul
Every time I look at the picture of the engine compartment, I feel like I just ate a double cheeseburger and super sized fries. How did you get all that in there anyway?

For popping the hood partially open this is a cut and try thing. There is considerable air pressure at the base of the windshield which might actually stall anything from coming out of the gap. This will be a situation that changes with speed probably better function at low speeds than high.

Another trick is to place an air dam under the radiator frame, this will create a low pressure area behind it, which is essentially the engine compartment. This will pull harder on the incoming flow thru the radiator and will tend to create a low pressure area under the hood. This could actually pull some back flow from the high pressure area at the base of the windshield into a gap between the hood and cowl.

Totally crazy would be to plug all passenger compartment connections with the cowl vent. Then put some holes from it's plenum behind the firewall into the engine compartment. At low speed the engine room would vent out the cowl while at high speed the high pressure area would force air in. However, keep in mind that at 100 plus miles an hour the last thing you want is high pressure under the hood, unless you're at V2 and rotating to take off.

I have no idea where you're finding space for 3 inch down tubes, which would work but where are they going?
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Old 06-25-2008, 05:11 PM
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LOL Yeah, she's pretty tight in there. The funny thing is, I have more room to change my plugs than the factory Buick does.

Thanks for the ideas.
Can't do the air dam because the intercooler scoop sits there.
I guess i could pop the hood and put in some sort of safety latch, but I'd like to find another way to get the air out.
The 3" tubes would fit from below. They would go up between the block and frame rails and end just below the headers.
I'm just trying to figure out what angle I should cut the bottom end at.
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Old 06-25-2008, 05:35 PM
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Not sure about the pipe angle. Try using some clear tubing with 1 end in a container of water. Hold the other end at different angles while blowing air across the end with an air blower on air hose. See if it will draw/siphon the water up the tube. May work, may not.
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Old 06-25-2008, 06:47 PM
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I'm going to mention another possible cause for your overheating at speed.
*
About 25 years ago I put a Ford 302 in my '80 Datsun 200SX.
I had the same problem you've described, overheating at highway speed, but OK at city traffic speeds. I tried adding fender vents, from an early 80's Trans Am, tired taking the hood off, put a smaller radiator in series with the main radiator. (I had an electric fan blowing through the smaller radiator exiting the left front fenderwell.)
What finally cured the overheating was removing the front bumper. It all boiled down to not enough airflow at highway speeds, and the bumper was blocking enough air to cause it. I ended up removing a section of the front bumper and all was well.
Just a thought.
JA
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Old 06-25-2008, 07:22 PM
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Quote:
Originally Posted by quick72toy
LOL Yeah, she's pretty tight in there. The funny thing is, I have more room to change my plugs than the factory Buick does.

Thanks for the ideas.
Can't do the air dam because the intercooler scoop sits there.
I guess i could pop the hood and put in some sort of safety latch, but I'd like to find another way to get the air out.
The 3" tubes would fit from below. They would go up between the block and frame rails and end just below the headers.
I'm just trying to figure out what angle I should cut the bottom end at.
I would think that someting from about 30 to a 60 degree angle (long side faoward) would pull a pretty good vacuum with the surrounding air passing by them.

Bogie
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Old 06-25-2008, 11:54 PM
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It looks like I'm going to have to experiment a bit with the angle. Might look up some race car wing designs, and see what info I can find there about optimum angles, negative pressure, and hope I don't get too side tracked. LOL

JA
I hear you about the bumper, but The car would look really funny if I chopped it.
I am making a small scoop/shroud for the front of the rad to try and direct more air into it. I guess every bit helps.


Thanks all.
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Old 06-26-2008, 01:05 AM
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Higher temps on the highway are rarely from underhood heat. They are either from not enough airflow or not enough radiator. I know you're trying to vent underhood air, but rarely is that an issue. The entire bottom of the car is in a pretty low pressure state. Chances are its sucking air out as fast (if not faster) than it can get through the radiator.

Just my 2 pennies.
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