That's one of the stupidest things I've ever read. The entire engine compartment is open on the bottom. A cowl does draw air in from the rear of the hood, but it is certainly not going to do any "counteracting the air being pushed through the radiator". If the engine compartment was completely sealed other than the radiator opening and the cowl, then yeah, there would be a problem. If anything, a cowl hood will increase convective cooling by pushing air over the engine block.

 

wythors,

Do you have a cowl hood? It would be interesting to tape a string on the cowl and see if it acts as a vent when stopped or in slow traffic and then as an intake at higher speeds. It would seem either case might give a lower pressure area to improve airflow through the radiator,

I'm looking for ways to lower engine temp and I believe airflow is going to be the answer.

 

I'm going to try this just to say I did it.

 

I like how they say that, but have no proof of it being a fact.

 

Weren't the original Camaro cowls used on the TransAm cars open at the rear for the high pressure but sealed to the air cleaner to provide not only "cold air" but a highpressure "ram" effect? Seems I remember these working pretty well, but as far as engine-bay pressure the cowl was not creating any negative pressure.

 

That is exactly correct. Leaving any hood open near the cowl will result in less airflow through the radiator.

There is high pressure at the base of the windshield and therefore the back of the hood. There is also high pressure at the front of the radiator. The pressure differential across the radiator is what determines the airflow through it. High pressure in front of and behind the radiator means that there is no pressure differential across the radiator and therefore no airflow.

 

have ya'll found engines to run cooler in competition with no cowl?

 

I run a cowl hood on my 86 GT. While normal driving, I use an air cleaner ( 14" round style) and when at the track, I use an air pan less air cleaner.

When I shut the car off, under normal conditions, the opening for the cowl does let heat out.
When I'm at the track, I open the hood to let the heat out, unlees it's during True Street ( closed hood policy)
Even during this time ( hood closed) the air pan does not seal up completely and does still allow some heat to escape, more than a stock flat hood.

To help cool the car, I put a piece of sheet metal between the front bumper cover and core support. This directs the air coming in through the front (remember it's an 86 with the single opening in the front) to go through the radiator and not up over the core suppoort.

Do I have any scienctific studies for any of this working? NO, I don'tnothing other than watching how my car cools down by the guage. When it had the C4 in it, I was trying alot of different things to keep the car cool. This things just seemed to help my car.

 

To help cool the car, I put a piece of sheet metal between the front bumper cover and core support. This directs the air coming in through the front (remember it's an 86 with the single opening in the front) to go through the radiator and not up over the core suppoort.

.

Do you have any pics of the placement of the sheet metal that you installed. I am curious as I am running a 94-95 style radiator in my Coupe and interested in airflow for highway/interstate speed with more rear gear.

Thanks
Jeff

 

Great! Let us know what you find out.

 

wrb752,

I'm not saying that a cowl hood with an opening at the back is going to result in zero airflow through the radiator, just less.

Airflow through the radiator is a function of pressure across it. If the pressure differential is zero (the pressure on the front and back is equal) there will be no airflow. If the pressure behind the radiator was greater than in front, there would be cooling because there would be airflow, even though the air is flowing "backwards".

Yes, we've done testing at road race tracks on this very thing. Run the car several laps on a test day while monitoring the engine coolant and oil temperatures. Then raise the back of the hood a small amount and repeat the test. We did this several times with the hood raised different heights at the back. The higher the hood, the higher the coolant temperature became. In the 3 lap tests we ran, the oil temperature didn't change a significant amount. If we had run the tests for a longer period of time, I think it would have gone up some.

 

How does raising the entire hood equate to a cowl hood. When you rasie the entire hood you change the way the air flows over the entire hood and the top of the fenders. I would have to think that with the entire hood raised in the rear, you now have uncontrolled air coming from where ever the gap allows it to enter.

I know that for a fact that when my brother put a cervinis 2.5 cowl hood on his super charged 90 GT his temps dropped when cruising on the high way. That was the only difference he mentioned.

 

On my Coupe and on another person Vert with cowl hoods both with AOD's, I actually noticed one full mark on the heat gauge lower with the cowl. I guess maybe it depends on How Fast and for How Long.

 

I'm going to guess that Jack is talking about an SN-95 or newer, while most of us are talking about fox body. If so, there may actual be a difference between the design of the front noses.

 

I will agree also with the above the storm'n norm hood on my car cooled better on the interstate but back to norm when traffic

 

heat rises, so dont you think and opening in the hood, would help extract heat more...... plus i have a stalker front nose , the lower part of the bumper is more open than stock plus it has an opening in the grill, plus 3 core alum rad with 2 slim fans staggered, it runs around 170 degrees all day long, guess this thread doesnt apply to me

 

Did you read anything in this thread? Just like to inject some random nonsense once in awhile to get your post count up?

 

We did our testing on a Fox body car (1987). It had a stock hood. The rear of the hood was raised up by installing spacers between the hinges and the hood. This made it easy to adjust the height of the hood at the back. After the hood was closed, the sides of the hood were taped shut all along the edge. This is a standard thing to do on most road race cars. I think the resulting behavior translates directly to a cowl induction hood with an opening at the back of it.

There are three major scenarios going on here, which I don't think is clear yet. In each scenario different mechanisms are dominating the cooling behavior.

An internal combustion engine generates mechanical energy by first generating heat energy. The more mechanical energy you want out of it, the more heat it generates. To keep the engine temperature constant, the cooling system needs to remove just as much heat from the engine as the engine is making (not exactly true, but close enough for this explanation).

When you have a car on a road course, the engine is typically at full throttle at least 60% of the time and the average speeds are high. As a result, the engine generates a lot of heat and the cooling system can transfer all of that heat into the air due to the large volume of air going through the radiator from the high average air speed. In this case, you are relying on the high air pressure differential across the radiator from the high air speed, to force a large volume of air through the radiator and keep the engine cool. If you do something to reduce the pressure differential across the radiator, you will reduce the volume of air going through it and the engine temperature will go up.

Driving on the street, the average throttle percentage is very low, maybe 8%. Take the case where the average speed is medium (45mph). The engine is making very little heat and the average air speed is high enough to keep the plenty of air volume flowing through the radiator. As a result, the cooling system has a very easy time keeping the engine temperature constant and the thermostat is probably only open 20% of the time. In this case, it won't make much difference at all what type of hood you have, since there is plenty of airflow through the radiator. Even if you reduce the airflow through the radiator by 20%, the thermostat will then only be open 30-40% of the time. This is still plenty of cooling system capacity for the engine to be kept at the thermostat temperature.

Now take the case of driving on the street in stop and go traffic. Very low throttle percentage (3%) and essentially zero air speed. The engine makes very little heat. The only airflow through the radiator is going to come from whatever fan you have on it. Without the fan, the engine will overheat, despite that fact that is barely making any heat. In the situation with the fan providing all of the airflow, anything you can do to help the fan create more airflow through the radiator will help a lot. Using a cowl induction hood will help this. It will be easier for the fan to push the air out of the engine compartment and as someone else pointed out above, the heat in the engine compartment rises, actually creating its own airflow that pulls air through the radiator.

 

Heat? Heat ? I would think that the problem with heat is when you are stopped in traffic or parked, Or when you shut the car off for the first few minutes the heat goes up and then back down that's when a cowl is nice it lets the heat out. And the fan blowing it back out the cowl when not moving has got to help am I right?

 

Did you bother to read post 22?

 

As jack allready stated it comes down to pressure differential the radiator being the restriction. Add more pressure to the backside of the radiator and it WILL NOT get the same ammount of flow through it. Seems pretty cut and dry to me :shrugs:

 

Thanks Eric

 

No problem man.

 

from what i gather (and i do understand this is not highly accurate at all) but think of ur house and u have the window open on one side. ull notice you only get so much air through it, but when u open one on the opposite end you get a draft. but even still no matter how hard the air is blowing in only so much can pass through and exit at one time. (the was what came to mind real quick)