Guess this in an engineering question as well as style and production cost question. If you look at any Model T, A, or '32-34 Ford hood you know how the louvers look, and allow hot air to exit the engine compartment. If they were reversed, with the slit facing forward and the bend facing the inside would the same amount of air flow or more? The time and cost of making the paint look good is the main reason this wasn't done IMO. The boss told me I was nuts for thinking about this,...........I'm not, am I?
The louvers work because the airflow over the vent creates a low pressure area. That effectively ****s the hot air out of the engine bay. I'm pretty sure facing them forward wound negatively change the effectiveness of the louvers. If you look at any cars that had vents, they face backwards (like the Shelby Cobra for example)
No, a louver is made to vent the hot air from an engine compartment. Hot air trapped inside has the same tendancy to rise as it does out side. But with a solid hood, it gets trapped on top of the engine and can't vent. This builds a high pressure area above the engine that forces incoming air to go down to vent out. In many cases this high pressure area above the motor can get so big that it literally blocks incoming air from geting through the radiator. Alieviating this is how a louvered hood helps more completely vent that compartment thereby letting cooling air flow more readily through the radiator. Now, flip those louvers around and scoop air into the compartment and you right back to creating a high pressure zone right above the engine. Granted this time it is "cool" air, but it still is going to hamper the flow of air through the radiator itself, just as it did in the first example. I proved this to myself years ago when a "dwarf car" client came to me to get his hood louvered. I did a nice traditional pattern with the louvers venting as usual, and upon his picking it up, he promptly freaked out! He had always been told that the louvers should face forward and scoop the air. I offered to redo the pattern his way if he remade the hood (very simple with these cars) and I did. I also told him to keep the other, as his would overheat things... Guess which one he ended up painting and running?
Here is a Packard Twin Six race car with what I call reverced louvers, Ferrari GP cars in the '50's and early '60's used this style as well. Looks like they scoop air out.
You know . . . , Barri is said to tell the story about how they used to give the night watchman a dollar a night to let them into some sort of military or contractor facility to punch louvers in the panels for his customs back in the day. They did not have one in their shop. Only deal is . . . , the louver press was for locker doors and it produced huge punched louvers. Look at some of the early Barris cars and see if this is not evident!!
To me, The top row, Forward facing. bottom two rows - punched on the opposite side, so air flows to the back side. Forward facing lourvers would collect such things as Rain WATER and bugs.
You want a positive air pressure in front of the radiator and as much negative behind it to remove as much heat as possible.
Gents, he is asking how it would work if the raised portion of the louver was to the "inside" and facing forward, not just reversed to act as scoops. 37Kid, I don't think it would make that much difference as it will still let the air flow though the radiator flow out easily enough and the air flow past the slots will create a bit of a low pressure effect drawing air out.
Wow, I read that three times and I didn't pick up on that untill now! And Mr48chev is correct, doesn't make any noticable difference. I have done several reversed over the years, they seem to be just as effective.
Thanks Mr48Chevy! I think posting that Alfa photo is worth the 1,000 words I needed to explain the question.
Sanding louvers ****s, both sides **** the same as I've sanded both. I don't think that was a consideration as to which way they face.
Ooooohhhh! It`d be a little hard to pinstripe them. Might create more wind drag if shootin for a record at Bonniville. Would collect more water in the engine compartment in a rainstorm. But it was taboo to have an outie belly ****on when you were a kid. Might have to be careful opening a hood with a piano hinge in some instances.
The effect is described as the Bernoulli Principle. See http://library.thinkquest.org/2819/bernoull.htm for a more in depth discussion and a good diagram. Normal or reversed it matters not, the high speed air rushing over the panel creates a difference in pressure between the inside and outside of the panel causing the hot air to be drawn from the engine compartment. Simple and effective ventilation.
I brought this up a couple years ago since most european cars ran them inward. I think they would look cool and I was thinking about using them on my '34 after seeing them on a Starbucks expresso machine of all places. You would have to reverse them inside out and flip them up side down so no water could creep right in.
It's not the same as your louver question but,while we're thinkin' air flow.... http://en.wikipedia.org/wiki/NACA_duct Smokey
Bob, i know this isn't exactly what your question entails but i've always liked the louvers on my favorite Hotrod, the Pestana & George track roadster. One particular feature of this car was the cooling system consisting of air and water. The water flowed through one of the round tube frame rails into a very thick radiator that sat very low, almost touching the ground. Water capacity was 10 gallons. The air cooling is very trick. Entering through the louvers on the nose into the engine compartment it then flows through firewall mounted airducts on each side of the car and exits through the louvers punched into each door. Would the same principal work if the door louvers were punched 'in'? I don't think so as the exiting air would've re-entered through the next louver and so on. Just my 2c.
Sorry but I goota call BS on this one, or at least half of it...the hot air in the engine compartment has nothing to do with a high presure area over the motor. Yes, warm air rises when in a environment of cooler air. Heat cannot create any pressure differential unless it is a closed system(constant volume). Unless you have a constant volume you are working with, the temp cannot make the pressure go up. Wind speed can give a pressure differential on a given surface, which is what happens to the front of your radiator when driving. yes, louvers theoretically can give better cooling to any car as your inlet is the surface area of your radiator and your exhaust is the underside of your motor and any leak path out of the engine compartment, which louvers would increase. Louvers are really only needed if you have a full belly pan where your exhaust path from the incoming hot air form the radiator and radiant air coming off your motor has no place to escape. this is why you traditionally only saw them on race cars back in the day. And yes they will help cool any engine quicker once you have stopped and turned off your motor, as the rising hot air coming from your heat soaking motor can escape through the louvers, especially if they are in the hood, generally the highest point on the engine compartment. On a related but different note, regarding forward facing and reversed(inward facing) , as stated above its all about Bernoulli. With either the traditionally faced or forward facing , both of these will create lots of turbulance along your nice flat surface hindering the effect they are intended for as teh air is detached from the surface. With an inward facing louver or we can call it an innefficient reversed NACA duct, your boundary layer of air stays more attached to the surface of the flat panel in question...this attachment and higher velocity of airflow increases your extrusion of warm air. See, louvers are cool......but the real question, is it louvers or louvres? I guess it's louvers on our hotrods and louvres on Brit cars huh?? JK...Hans
Boy Hans' Rod and Cycle, I'll have to take it that you don't spend too much time trying to cool high performance stuff in AZ type extreme heat! Sorry, but I have to stand by what I wrote earlier. It's principal that I was taught as a kid in science cl*** and in the "old time" radiator shop I worked in, and judging by the amount of stuff I manage to help cool with undersize engine bays, It works. I do agree to some small extent that the only cars that "need" louvers are those with full belly pans... Kinda. In the summers around here, my main clients cease to be the hot rod crowd, and about May first switch to my Jeep and rock crawler crowd. Ever see a late Cj engine compartment? Very constricted, and not a lot of room for air to flow past the engine, toe boards and inner fender panels. Now combine that with very slow speeds and only semi efficient fans, and a recipe for overheating is made. Still no full belly pan to completely shut off airflow, but enough to restrict it heavily.
Now you see that paragraph is much more correct. I'm not saying they dont help, they do! Especially in the cir***stances you just wrote, like the rock crawlers and high temps sitting in traffic...Yes louvers helps here as the hot air can escape by rising through the extra openings in the hood and side panels. I spent the first 35 years of my life in Texas, I am well aware of the task at hand of trying to keep a car cool in 100+ degree heat be it at the race track or in traffic. My big disagreement was stating that the hot air causes a high pressure area above the motor, it simply does not.This was a principle I was taught in getting my engineering degree. I'm not at all trying to start a louver war here, I just wanted to make your statement a little more true. Simply put, the Combined gas law states that the ratio between Pressure/Volume/Temp remains constant...PV=T so P=T/V...in order for P or pressure to increase either you Temp has to rise or you rVolume has to Decrease.....but you always have to have a Volume...in the open environment Volume is infinite so Temp can in no way increase your pressure..
You dont even need a belly pan to run into a situation where you dont have enough airflow. My wife's '63 Falcon has a V8 in it and there is very little space between the shock towers and the engine. Aftermaket intake , Holley and the tallest K&N I could get away with pretty much filled the space going up, too. It ran cooler without a hood than it did with the stock/ unlouvered hood. And it runs cooler with the louvered hood than it did without a hood. If there is a bottleneck anywhere in your cooling system, you'll find it if you are driving in Arizona...
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