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I was thinking. I have had this hood vent idea for a good while now. I'll get right to the sketch..

Just look at the front end. Don't mind the huge BRE at the back.

 

m58545010.jpg

 

So say we close up the front end even more than it is there. Maybe half that size.

Would completely blocking off the engine bay and diverting air over the hood be a good idea?

What about useing the same hood vents but extend the front end out like the janspeed Z's hood with the Gnose buckets.

w91292650.jpg

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I think that would help to grab more of the air and force it over the hood rather then under the car.

 

I had of an idea of getting a cowl and instead of having the opeing right in front of the window where itll suck in air, have it further down the hood so air from the engine bay exits out the back.

 

Mabey both of our ideas would help if used together?

 

By the way thats a crazy looking Z.

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I have been playing with the front end treatment and underhood ideas.

I have completely sealed the front opening to the radiator.

I have ventilated the sides of the engine compartment(battery and clutch master areas).

I plan on ventilating the inspection lids.

I have the stock front radiator support to hood sealing frame the came on the 1973 model 240Zs(and the sealing rubber strip). I also copied this shape for my early 240Z.

I plan on placing "gill-vents" in the fenders.

 

 

The area I am puttiing some thought into is the hood it's self.

 

1. Nissan put a sealing lip on the rear edge of the hood opening.

 

2. We saw a surprising benefit to aerodynamics when the hood popped up during the tests.

 

My questions are...

1. How is the stock rear sealing lip of any benefit?

2. Is the airflow significantly different when the hood is up 1/2", 1", or 4"?... much higher than 4" will get into the view(with a race seat position).

3. Is the benefit to the hood popping up only present when it can come wayyyy up?

4. Would pinning the hood at the first opening stop get any real effect or would it actually prove detrimental unless it was opened too much to see out past?

5. If this is effective and drivers can still see out the windshield at it's effective height... would there be any need for 280Z hood vents?... or inspection lid vents? or gill vents? or any kind of vent ather than the hood sitting open at the back.

6. How shoud the sides of the hood be treated?

7 If this is tested in the tunnel... We might try entirely different hood shapes. I would like to see the effects of at least 2 different types of wiper-cowl fairings.

A. Concave(like a fillet)

B. another that is more of a hood-bulge that widens and transitions into the windshield in a more convex manner.

 

 

I remember seeing people setting the hoods to stay open at the safety stop point at auto-Xs 15 years ago. I remember someone stating that they had problems with radiator cooling with a cowl induction hood that was open to the engine compartment.

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Just came up with mabey a good idea. If you were to cut the hood around the middle and keep the back in the normal position and the lift up the front like your opening the hood but only like 3 inches. Then weld it all up so at the middle of the hood you have 3 to 4 inch gap that air can escape.

 

Not sure if its a good idea or if it would look good but it might help.?.

 

I have to wait till my cars all finished up and painted to do any kind of test fabing etc. Cant wait till I can.

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My thinking is that it transitions the hood into the winshield. This is similar to modern cars with steep hoods and laid-back windshields.

cutting the hood and raising it up further forward might just make things worse.

 

How about popping the hood and creating a fillet to transition the winshield over the wiper tray grill.

240Zsideviewwithhoodupfairing.jpg

 

...

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That sounds like a good idea. Im thinking that youd have a problem if the flip was to far forward on your idea. Ive seen some trucks with something like this at the base of the windshield.

 

I was thinking something like this but you probably know alot more about what would help and what wouldnt.

240Zsideviewwithhoodupfairingn_thumb.JPG

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I remember seeing people setting the hoods to stay open at the safety stop point at auto-Xs 15 years ago. I remember someone stating that they had problems with radiator cooling with a cowl induction hood that was open to the engine compartment.

 

I've heard / seen this also. Is this not conflicting data? How is popping the hood different from having the rear of the cowl open?

 

At present I'm about to close off the center rear of my cowl hood - I need the cowl for intake clearance but want to improve cooling and aero.

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This may be more seat of the pants type experience, but here is my .02 cents.

 

I had to take the car to have the exhaust put on. (headers only) I took the car out, but forgot that I did not have my hood latch installed. The hood lifted up quite a bit while I was on city streets. Enough to seriously worry me about blocking too much vision...as well as the cops seeing the car in a less than road worthy condition.

 

I can't recall how much it came up, but is was more than a few inches.

 

Anyone want to take off their latch and go for a quick drive and see how much it pops up.

 

PS. The hood would sit back down most of the way whenever the car was stopped at a light.

 

PPS. My car was much more stock in those days. re no aero other than the airdam.

 

Scott.

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I have seen a valence on a Z just like y'all are talking about that covers the wiper arms. Very slick looking. I can't believe that I didn't get a pic of it. It was on a red roadster Z that had a dash that looked like a ferrari and has round tail lights.. It has been on the internet before so maybe I'll find some pics.

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I've heard / seen this also. Is this not conflicting data? How is popping the hood different from having the rear of the cowl open?

It's open all the way down the side of the hood, not just at the back like a cowl.

 

When they did the aero testing the hood popped open and opened up about 6 or 8 inches and stayed there, and the overall effect was beneficial I think. It's in the aero thread if you guys are interested.

 

Limiting strap is a good idea. Otherwise when you hit the brakes your visibility may become "less than ideal". :lmao:

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I'm still kinda confused, and I'm sure i need to look over the data again and again to fully grasp some things, but didn't we discover the the cowl will let IN air? Then why did popping the hood help? Is it because there's more air trying to get out than in?

 

If this is the case then opening it too much will relieve too much pressure and air will just go IN and then DOWN causing more air under the car, and more lift.

 

And if we add more venting without sealing off the air coming into the bay then we decrease air pressure in front of the radiator, and thus lesson it's cooling ability.

 

But if we close up the front end, and limit the air getting in to JUST the radiator we don't need as much hood venting yes? And if we increase the air openings in the hood this could create a slight vacuum pulling air through the radiator right? How can be balance this or even guess where the balance is? Cars like the Ford GT have HUGE openings in the hood, but I think the reason why that works is that the hood is shaped in such a way that air can still come over the hood and if anything push down where the opening is, while the air coming out creates pressure pushing the air up, helping the windshield (at least this is what I've heard ford claim).

 

One thing that worries me is that if we vent air too far forward in the engine bay we could loose some air cooling abilities on the engine. How much do you guys think this even matters? Possibly not at all? Keep the oil and coolant cool and it should be fine right?

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I have a carbon fiber hood (fiberglass bottom/carbon top) which is still very light..

 

when its hot outside.. to prevent heat soak I open the hood which allows all that hot air to escape...

 

yes i've driven it unlatched at 100mph plus and I did not see it rise that much.. only 2-3 inches.

 

maybe its the airdam I have

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I'm still kinda confused, and I'm sure i need to look over the data again and again to fully grasp some things, but didn't we discover the the cowl will let IN air? Then why did popping the hood help? Is it because there's more air trying to get out than in?

 

If this is the case then opening it too much will relieve too much pressure and air will just go IN and then DOWN causing more air under the car, and more lift.

There's a lot going on here. When you just pop the hood, you open up a long slit all the way down both sides of the hood in addition to the area at the cowl. Tests would need to be done to determine what exactly happens in this situation. It could be as you said that more air gets evacuated by the air streaming over the hood than gets pushed into the cowl area at the back. The air doesn't have to just go out or just go in.

 

But raising the hood farther eliminates the high pressure area at the windshield, because the air isn't hitting the windshield as directly anymore. I think it's probably fairly safe to say that the hood opens until the pressure on top and bottom is relatively neutral. How the air flows through the radiator when the hood is open 6" is another thing that would need to be tested.

 

And if we add more venting without sealing off the air coming into the bay then we decrease air pressure in front of the radiator, and thus lesson it's cooling ability.

I would venture a guess here to say that you can't vent enough out the top of the hood to cause a lack of air flow through the front of the car. It's possible that you could divert the air up and over the rad core support and out the top of the hood, but I don't think it's likely with anything close to the stock front end. Maybe if you closed off the grill way too much and didn't seal the front of the car to the core support... don't know.

 

But if we close up the front end, and limit the air getting in to JUST the radiator we don't need as much hood venting yes? And if we increase the air openings in the hood this could create a slight vacuum pulling air through the radiator right? How can be balance this or even guess where the balance is? Cars like the Ford GT have HUGE openings in the hood, but I think the reason why that works is that the hood is shaped in such a way that air can still come over the hood and if anything push down where the opening is, while the air coming out creates pressure pushing the air up, helping the windshield (at least this is what I've heard ford claim).

That's what I'm thinking...

 

One thing that worries me is that if we vent air too far forward in the engine bay we could loose some air cooling abilities on the engine. How much do you guys think this even matters? Possibly not at all? Keep the oil and coolant cool and it should be fine right?

If the air that comes in the front opening HAS to go through the radiator, then I don't think this is possible.

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Venting the sides of the hood to simulate the patially open hood without actually opening it might look something like this.

hoodventing.jpg

 

The green is the engine air inlet.

 

 

 

This would be the same as the louvered hoods from MSA. This might help more than anyone ever thought. I think it warrants testing a louvered hood in the future.

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Guest TeamNissan

I actually suggested this 3 weeks ago in my aero thread.

My thinking is that it transitions the hood into the winshield. This is similar to modern cars with steep hoods and laid-back windshields.

cutting the hood and raising it up further forward might just make things worse.

 

How about popping the hood and creating a fillet to transition the winshield over the wiper tray grill.

240Zsideviewwithhoodupfairing.jpg

 

...

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I don't claim to know anything about aerodynamics but I see a lot of pieces here that fit together but no one is seeing what I'm seeing. Taking bits anf pieces from what everyone here has said, I come up with the following.

 

If you want to vent the hood with hood vents, the vents have to be way forward of the trailing edge of the hood to stay out of the high pressure area created by the angle of the windshield in relation to the hood. Opening the hood and leaving it on the safty latch doesn't do much to vent the underhood air but it does do something to releave underhood temps. How does this happen if there is a high air pressure system at the base of the windshield? The answer is in the side openings of the hood. I can to this conclusion because a cowl induction hood causes temperature issues. The additional air that comes in caused by the high air pressure system at the base of the windshield hits the air that is coming through the radiator in effect slowing it down, and all of this air competes to exit under the car. With the hood popped, the radiator air has a way to escape out the sides of the hood and around the car.

What I would like to try, and will do so on my car, is to try to vent the underhood air to the sides of the car with someting like TitaniumZ has done at the TC cups. Also, once the front of the car is has been sealed and air can only enter the radiator or go over the hood, I'd like to try to help the air go around the windshield. Areas of concern would be the A posts at the drip rails and the windshield gasket.

 

I'm interested in what everyone thinks. Am I off my rocker? Not getting this at all?

 

Joe

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IM guessing the reason you open the sides of the hood is so you dont have the high pressure of in front of the windshield like with a cowl. The air would be moving faster along the edges of the hood then at the back of the hood creating lower pressure.

 

 

I'm interested in what everyone thinks. Am I off my rocker? Not getting this at all?

 

 

I give the same disclaimer.

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I think to know where to vent a stock hood properly we should know where pressure starts building in front of the windshield. I think the middle of the hood where it is relatively flat would be the best place to suck air out through the hood.

That just seems logical...

The front of the hood has a good angle on it so it hits relatively clean air. The rear has pressure built up from the windshield.

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I don't claim to know anything about aerodynamics but I see a lot of pieces here that fit together but no one is seeing what I'm seeing. Taking bits anf pieces from what everyone here has said, I come up with the following.

 

If you want to vent the hood with hood vents, the vents have to be way forward of the trailing edge of the hood to stay out of the high pressure area created by the angle of the windshield in relation to the hood. Opening the hood and leaving it on the safty latch doesn't do much to vent the underhood air but it does do something to releave underhood temps. How does this happen if there is a high air pressure system at the base of the windshield? The answer is in the side openings of the hood. I can to this conclusion because a cowl induction hood causes temperature issues. The additional air that comes in caused by the high air pressure system at the base of the windshield hits the air that is coming through the radiator in effect slowing it down, and all of this air competes to exit under the car. With the hood popped, the radiator air has a way to escape out the sides of the hood and around the car.

What I would like to try, and will do so on my car, is to try to vent the underhood air to the sides of the car with someting like TitaniumZ has done at the TC cups. Also, once the front of the car is has been sealed and air can only enter the radiator or go over the hood, I'd like to try to help the air go around the windshield. Areas of concern would be the A posts at the drip rails and the windshield gasket.

 

I'm interested in what everyone thinks. Am I off my rocker? Not getting this at all?

I thought that the first part of this sounded pretty similar to what I said in post #14, so I didn't feel a real need to respond. The rest is all conjecture. But if that's what you're looking for, here is some for you... :wink:

 

I'm not sure about the effectiveness of the TC area modifications when done alone, and I think their usefulness would be greatly affected by the shape of the airdam and the front fenders. Again looking to the NASCAR model which I believe is overlooked too much in general, if the front of the fenders protrude past the wheel openings by a fair amount this should create a vacuum in the wheel wells which would assist in drawing air out from under the hood and make the TC mods and fender vent mods more effective. If someone was using the MSA IMSA flares which are basically aerodynamically backwards in my opinion (because they expose the front of the tire and have a large protruding mud flap type shape in back) then I think the TC mods would be much less effective, if they were able to do anything at all.

 

I'm also not sure about the drip rails and windshield gasket. My hunch is that it would be better to have the windshield mounted flush with no gasket protruding into the airflow, and have it fastened with clips like a real race car. I have no idea where one gets the clips from though. I've done some quick searches on the net and haven't been able to find anything. On my car I've already cut off the drip rails in the process of fixing rust, so I think my goal is going to be to get the windshield net and quarter window flush with the outside of the car. I will also use the small mesh type window nets as opposed to the 1" thick nylon strap type, as my gut tells me that the small mesh type strung tightly will be better in terms of aero. I think a flush surface is better on the side of the car than having a bunch of different layers like the stock Z does, with the drip rails sticking out into the airflow and the quarter windows recessed back from the body line.

 

By contrast I bj seems to think that the drip rails have a beneficial effect, tending to force more air out and around the window openings, but I'm not sure that I agree with that. I think it would take more testing to know who is correct on that point, but I'm basing my opinion on the majority of new car designs where the drip rails are integrated into the roof instead of hanging out on the side of the car. But when you're racing with the windows open I can't say for sure who would be right.

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