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Hood vents versus hood cowl/scoop

Tryfan

NAXJA Forum User
Location
New York
I was looking to let some heat out under the hood and I wondered if anybody had any opinions on which would be better hood vents or hood cowl/scoop?
 
Vent and here is why.

In order for air to pass through the radiator, it must have somewhere to go. You cut a hole in the hood, or the fenderwells for that matter, to let the air pressure out from the engine bay. The drop in the bay pressure will allow more air to pass over the radiator tubes.

Here is the kicker, the "where do I put the hole" kicker.

There are two basic places to cut. Near the froont of the hood and past center nearer to the back of the hood. If you wish to increase flow at higher speeds, you cut at the front, lower speeds, at the back.

You can test it yourself by taping 2" pieces of yarn onto the hood of your Heep and taking it for a drive. You will see the pressure areas and air flow develop on the hood by how the yarn reacts. In a low pressure area, it will stand up. You will be able to see exactly how the air moves across the hood by the pattern the yarn makes. Use a maximum 6" grid. When you find the lowest pressure area on the hood, that would be the best functional location for a vent. Get the best scavenge effect.

Here is where I mounted mine on the 98:
P9090002.jpg


And here is where I put them on the 97 I had:
jeepn21.jpg


Scoops are for cold air intake...

Before anyone asks, the vents on the Black 97 are from a Nissan Z car. As you can see, I mounted them as far back as possible. When I did my current Red 98, I was investigating the engine cooling system. I was working with Davies-Craig (out of Australia) to get the EWP115 system installed and fully functional. Poking these vents (which total 72insq) made an immediate drop of 7F in the average engine temperature.

Which is a good drop.

So, there is my .02 on the subject!
 
Thanks O Gauge that was just the info I was looking for.
Do you get any problems if you get heavy rain direct onto electrics etc
 
I have a drip pan for the winter (it doesn't rain here much in summer) to avoid direct rain. The drip pan does defeat the purpose a bit but when it's cool it doesn't matter. I take it out in hot dry weather 4 months out of the year.

If it's going to rain alot and the Jeep is parked for an extended period I just cover the vents with plastic. When I'm driving in the rain, I don't worry about it. It's kind of a pain but it's well worth having the vents wide open when it's 100+.

I'd really rather have a cowl hood open in the back to avoid all that , but not a scoop.
 
In both cases, I bent up a set of drip pans. Used the thin aluminium you can get from any of the Home Depot type of stores.

Took some measurement with the vents on the bench, drew out the pattern, made a template (out of paper) just to be sure, drilled/cut the Al and put it together.

I have the pans open both at the front and the rear of the pans, the better to vent the heat, with a large drop in the rear to direct the water to the back.

But it is an interesting experiment to see the air flow. I went with the vents I am currently using due to the fact that they asre what I found in my local pull & pay... All you really need is to vent the Driver's side. Where the heat is. Had the vents been shaped differently, I would not have installed on both sides.

Everything stays dry.
 
I have a set of those in the shop, waiting to be installed. Any tips, tricks I should think about?

If you're worried about water just don't install them directly over the TPS/Throttle body or the distributor. The Z vents are smaller than the Le Baron vents so you'd be OK mounting them more towards the rear. Look at the supports under the hood. You wanna avoid those when cutting and if you have a under hood light remove/relocate/avoid. I had very good luck using a jig saw with a fine blade. Protect the paint with masking tape, saw right thru it.

...and a shout out...my brother lives up there...I'm only an hour away.
 
I see how vents are better. however, I wanted to do a cowl hood for some venting and style. is there anything WRONG with them?
it would be very easy for me to do one like this and I was very interested in its function/mean look
just like this (not mine). with some sort of cover for winter

8cowlhood.jpg
 
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