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That's the Bernoulli principle you're talking about with the bottle example. The problem is that there is a stagnant high pressure area right at the cowl, hence the invention of the cowl induction hood. The cowl induction hood takes the pressure that normally exists at the base of the windshield and forces it into the engine compartment where there is usually a big 4 barrel waiting. It wouldn't make sense to suck air away from your carburetor.


There are some things about the Z that make cowl exduction more likely, for instance the cowl itself is relatively deep and the windshield is pretty curved. One guy on here tried the yarn test and found the yarn alternately going into and coming out of the hood. In my mind a vent at the back of the hood is far from the best way to get air out. Bernoulli's Principle would work much better in the middle of the hood, since the cleaner and higher velocity airflow you have the stronger the suction created, and the farther you are away from the windshield and the front of the car the more airflow there is going to be.

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There was some talk about using a manometer to test the pressure on the hood, can't remember if anyone did it.   The black car has "alligator teeth" louvers which will extract more air tha

Welcome to the forums, I will say this is dangerously close to skirting the rules there. If you would like to sell your product please feel free to make a thread in the vendor forum.   I do

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Thank's for the response.

If you dont mind I would like youre opinion on my situation and thought.


I am installing a turbo fuelinjected inline 6 in my '73 240z. The cowl induction theory wont be a performance robing issue in my eyes.

Now I believe that the induction could only ocur at lower speeds but even then the known positive pressure (high pressure area) in the engine compartment wouldent allow this. Most cars with cowl induction hoods have a small or almost no grill, unlike the Z.

The reasoning I am left with is, if the cowl isn't so great (large) to cause to mutch turbulence at the windshild the added volume to the engine compartment (from the raised center portion of the hood ie. cowl). And with the aid of the Bernoulli principle and posiably some reduction in the front grill. Then it will creat lower pressure in the engine compartment and give down force as the air is pulled out and over the car. As well as limit air from traveling under the car. The air under the car has more pressure than the air going over the car, making the air take the path of least resistance up and out. After all it is known that if you leave the hood unlached on a Z the hood will rise. This can't happen if youre induction theory is correct. In the case of a 240 Z I think there is somthing else going on.

Looking forward to youre response, Thanks.


It is all for the greater good of the Z.

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  • 1 month later...

i did it. took the dremel to the hood.








i made the area of the vents a little larger than what i had taped out before. i have yet to hit the fenders with the vents. not sure weither to cut out a rectangle of the fenders, add the vents, then put them back in. or try patching a new piece of metal in with the vents. i am thinking to use the old metal because the fenders are contoured and im afraid it will not match back up if i do not.



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I have a different impression of what the cowl induction openings will do. This depends on a lot of unknowns, but...


The air at the base of the windshield is pretty high pressure. The rear cowl-opening will almost certainly take in a lot of air.


The front opening is pretty small in area, but it is also in a place that will have a lot of air flow, NACA inlet, etc...


I am willing to bet that BOTH the front and rear openings will see a lot of airflow if the opening can dump it under the hood.


I'll bet that a true COWL-induction airbox will see fairly high pressure. With a limited amount of airflow consumed by the engine, I think that the front opening will be overcome by the air entering the rear opening. Flow into the front will stall and possibly even allow airflow BACKWARDS, out of the front opening.



Here is what I have come up with so far....
















If the front opening was larger, perhaps by dropping the NACA inlet floor and enlarging the entry opening, You would begine to see flow through the cowl box from front to rear.

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Basically making a sort of pressure box right?


There's a guy my dad knows with a notchback VW that runs I THINK in the 9's (it does at least 140 in the 1/4) anyways, he has both his carbs fully sealed in a pressure box, with naca ducts running to them. He said that it gets up to around 3lbs of pressure on his runs, so I suppose even that would help the car get a little more power. Especially on a really high compression N/A car.

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  • 4 weeks later...

I'm 98% certain that Owen fabbed those vents. He was quite good w/ fiberglass. Just for shits & giggles, I'll share some pics from the racetrack today that might inspire. I've already made my one-off hood that will be unveiled in due time using directional louvering & NACA duct. The guy that did the louvering was one of THE old school Rat Rodders that essentially invented the technique. He is about 80 yrs. old and still does kickass work! Pics from the track, an '09 Evo Pace Car hood:





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Been meaning to post these pictures in this thread for awhile now. I'm hoping that my louvered vents will help evacuate hot air thats directly above the intake manifold and turbo as well as giving the pressurized air thats under the hood a place to escape. I don't have and hard evidence or data beyond my own observations, but it seems that the underhood temperatures are not as severe as the used to be. Eventually this summer I plan on sticking a temperature probe under there and finding out, as well as a string test at mid-highspeeds.






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WTF??!! Has anyone else had their photobucket pics spontaneously disappear?! Let's try this again...








"Sparky", I'm almost disappointed to see the public posting of those inverted louvers. I thought that I was the only one...hadn't seen them on ANYONE else's. Got inspired by an old 60's Jag. Oh, well, brilliant minds think alike ;~)

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I agree wholeheartedly! Absolutely LESS functional inverted; however, I was going for a certain 'undisturbed' aesthetic. You are spot-on regarding the idea of function over 'form'.


Yes, I'm under no delusion that my car is a "race" car. I wanted a way to vent underhood conditions with minimal aesthetic unpleasantness...I'm commanded by subtlety.


Sorry to steal your thunder 240Z2NV, great minds do indeed track similarly ;)

I was actually robbing parts off of a 280Z in a junk yard when I saw a Honda CVCC covered in vines. I was reminiscing while thinking of ways to waste money on a CVCC project when I spotted the louvers on the hood...I immediately thought of my Z and where to put the louver...alla Z31 turbo. It's a bit of a homage to the Z31T my dad used to have.

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They are pretty much as aesthetically perfect as one could hope.... Did you have them done the traditional way, or graft a section on with them completed 'off-hood'?


I went back to the junkyard the next day with my jigsaw and 200ft of extension cord and cut the corner off of the CVCC's hood. I figured they were already there and just about perfect as far as I could tell...why reinvent the wheel eh! My painter/body man was quite skilled so I had him weld and blend my new louvered panel in place.


Traditional methods are cool but can be prohibitively expensive, especially on the shoe string budget I had on this Z.

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