[firefish]

When fiddling with the airbox mod and removing the rubber grommet to let a little bit more cool air in I started thinking about the temperature under the hood. Even after a normal drive, normal as in for normal cars, I feel that the temperature under the hood is quite high and everything is rather warm, almost hot, to the touch indicating that the temperture under the hood is high even when driving (as in not much air flowing through the engine compartment). I cannot help wondering if there isn't a cure for this...

I have ordered the heat shield from RS Barn and that should help keeping it a bit cooler.

Has anyone tried wrapping the headers with "whatever it's called in english"?
I don't know how the air flows under the hood but what about opening up air outlets on top of the hood forward of the seal dividing the engine bay from the compartment holding the wiper mechanism, fan et.c (kinda like the ic outlet on the turbo but aft of the engine)?
I was also thinking about letting more air in in front of the airbox by opening up the sheet metal around the hood lock. Doing this in combination with above mentioned mods should get more and cooler air to the engine, allow excess cool air to sweep over the engine and evacuate through the hood vents, allow the air flowing through the radiatior to evacuate below the engine (assuming that that is how it is intended to work, but where else could it go?).

These mods should, if they work and my thinking is correct, reduce temperature under the hood substantially and as a result free a couple of extra ponies and also increase the life span of a few of the components under the hood. I am not about to cut my stock hood open but when I make my carbon hood I might as well add some vents to the design. I don't mind gutting the metal on the inside of the engine compartment though, not as long as it is classy done.

What do you think? Are there any traps here or am I missing something obvious (most likely)?

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[flash]

yes to wrapping - very effective - no long term reports yet on degradation of tubing - mine is ceramic coated though, which should help slow down the inevitable break down of wrapped tubes

i've done quite a bit of work on reducing under hood temps - what i have actually found most effective is adding the 3rd belly pan from the early cars to the other two, and closing up a lot of the places where extraneous air gets in

the idea was to create a negative pressure zone under the hood - it has worked very nicely

more air in bad - less air in good

adding more air under the hood is a very common mistake though that many make

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[firefish]

<!--quoteo(post=75632:date=Jul 15 2009, 10:23 PM:name=flash)-->QUOTE (flash @ Jul 15 2009, 10:23 PM) <{POST_SNAPBACK}><!--quotec-->yes to wrapping - very effective - no long term reports yet on degradation of tubing - mine is ceramic coated though, which should help slow down the inevitable break down of wrapped tubes

i've done quite a bit of work on reducing under hood temps - what i have actually found most effective is adding the 3rd belly pan from the early cars to the other two, and closing up a lot of the places where extraneous air gets in

the idea was to create a negative pressure zone under the hood - it has worked very nicely

more air in bad - less air in good

adding more air under the hood is a very common mistake though that many make<!--QuoteEnd--><!--QuoteEEnd-->
Omg, you are insanely fast when it comes to replying!?!

When you did your testing, did you also evacuate air at the back of the hood?

I assume that the idea by adding the 3rd pan is to let the moving air under the car pull the hot air from the engine compartment, kinda like an ejector pump, through the opening in the lower aft part of the engine bay?

I agree that it can be bad to let more air in if you screw up the way the air is supposed to flow. It is better to pull more air out that pushing it in and causing a positive pressure and thus effectively blocking more flow. This is why I was thinking about adding ducts at the back of the hood. There are some neat designs that create a lot of suction when air flows over them and I suspect that by putting said vents forward of the seal they will be located in a position where the air flows laminar and close to the hood. To much aft and the airflow rises to follow the windshield and you lose the suction effect (might even be a rotor there that creates an overpressure).

My idea is, in combination with the 3rd pan that I haven't heard of before, to add one more exit point for the air and thus even further reduce the pressure. And in addition to this redirect some of the air entering the engine bay through the nose to the airbox but still maintaining the negative pressure.

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[xrad]

I am not disagreeing with the above, but if you place pressure transducers on the hood, you will see high pressure just in front of the windshield and lower pressure (respectively) over the center/front of the hood. The air traveling over the car should be in general(not including wings and things) of lower pressure than the air forced through the radiator, but may be higher than air under car. Similarily, side vents appropriately designed, can do the same thing

If you can design a properly lipped vent placed just in front of or on top of the cam gears(you want to catch the most linear flow region to induce the Bernoulli effect)), much of the radiator forced hot air will travel to this low pressure region and exit from under hood.

BUT, it has to be designed properly in conjunction with the under pans.

Porsche designed a vent for the turbo intercooler for the same effect: more flow, better cooling. But if you don;t have the intercooler, you have to watch your design.

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[flash]

i did not add any venting - all i did was work with the engine bay, limit extraneous air from entering, force the air to all come from the radiator area, and then direct the air to the rear and out - the result has been good, and roughly 40 degrees dropped, and a lot more even temperatures

the biggest changes though came from the heat shield and wrapping the header

i just did another mod a few weeks ago, but have not yet taken the measurements - i can tell it's working, but i can't quantify how much yet - i'll get to it soon though

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[firefish]

<!--quoteo(post=75636:date=Jul 15 2009, 11:03 PM:name=xrad)-->QUOTE (xrad @ Jul 15 2009, 11:03 PM) <{POST_SNAPBACK}><!--quotec-->I am not disagreeing with the above, but if you place pressure transducers on the hood, you will see high pressure just in front of the windshield and lower pressure (respectively) over the center/front of the hood. The air traveling over the car should be in general(not including wings and things) of lower pressure than the air forced through the radiator, but may be higher than air under car. Similarily, side vents appropriately designed, can do the same thing

If you can design a properly lipped vent placed just in front of or on top of the cam gears(you want to catch the most linear flow region to induce the Bernoulli effect)), much of the radiator forced hot air will travel to this low pressure region and exit from under hood.

BUT, it has to be designed properly in conjunction with the under pans.

Porsche designed a vent for the turbo intercooler for the same effect: more flow, better cooling. But if you don;t have the intercooler, you have to watch your design.<!--QuoteEnd--><!--QuoteEEnd-->

I have not seen any pictuers of how the air flows over the 968 but seeing as the windshield is quite steep I would assume that you are about correct of how the air flows.

But how much design did the engineers actually put into this? Is it really that there is no room for more improvement here? To be honest, the belly of the 968 doesn't seem that perfected in the aspect of airflow. And maybe that is the area to focus on - reducing pressure below the car. Perhaps the task of reducing underhood temperature starts with the rear bumper?

40 degrees, that's alot. Did that result in a measureable temperature drop in the intake air?

I'll start with the shield and with wrapping the manifold.

Perhaps the best solution is to start driving in the winter instead [img]style_emoticons/<#EMO_DIR#>/smile.gif[/img]

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[xrad]

Definately wrapping the headers will decrese heat. I use DEI wrap 1 inch with 1/2 width overlap... held in place with their stainless ball lock clamps (not the best, though). You can touch the header after a hard run and not get burned.

Trick is to soak the wrap first so that it stretches, and then wrap tightly. When heated, it shrinks just enough to make a real tight wrap. With practice, you can do a real nice job.

Not Porsche header, but one I wrapped.

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[flash]

i had no easy way of determining the temp change of the intake charge - i have to assume that since the intake manifold was cooler, so was the air inside it

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[Cloud9...68]

I've been reading through these recent (and not so recent) theads on underhood temperatures, so I have to ask the obvious question - what's the benefit of lowering the underhood temperature? Is it mainly to facilitate the lowering of the intake air temp? Thanks.

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[flash]

that, and increasing plastic component life span (heater control valve, hall sensor, etc)

some things don't want to be cooled down though, like the cat - you want that good and hot - another reason the heat shield works well - it directs all that heat down to the cat

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[Cloud9...68]

Ah, thanks for the explanation.

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