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FIENDISHLY SIMPLE AIR PRESSURES OVER AN EF FAIRMONT HOOD 

 

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 Post subject: Re: FIENDISHLY SIMPLE AIR PRESSURES OVER AN EF FAIRMONT HOOD
Posted: Tue Jun 16, 2009 12:30 am 
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good stuff - but one thing you said I thought was obvious - (apologies if this has been addressed in a reply - I only skimmed thru it..) you seemed surprised that there is a pressure zone at the windscreen - but this is why A9X and cobra scoops as well as aftermarket ram air type hoods by Harwood etc (as seen on US drag racing camaros etc) all face backward to the windscreen base

again, apologies if I've misunderstood you or not picked up on someone elses comments/replies

 

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 Post subject: Re: FIENDISHLY SIMPLE AIR PRESSURES OVER AN EF FAIRMONT HOOD
Posted: Tue Jun 16, 2009 12:36 am 
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I was a little surprised as I knew NOTHING about this before starting.

The BIG surprise was that the top of the windscreen is a low pressure zone before the top of the car. Like - from half way up the windscreen there is more air pressure inside the cabin at the mirror than there is on the outside of the windscreen at the same point! This would mean that if you put a small hole in the window at that area that air should be move forwards through the hole and out the car.

Uhm. As I repeat regularly, I am purely a car novice so anything I try may have been proven elsewhere or I may be barking up the wrong tree.

However, it is worth a crack! The few people who bought one of my phenolic spacers all seem happy enough... If I spent as much time trying to make a million dollars out of dodgy internet sites as I invest in the car..........................
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 Post subject: Re: FIENDISHLY SIMPLE AIR PRESSURES OVER AN EF FAIRMONT HOOD
Posted: Tue Jun 16, 2009 11:43 am 
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yeh, the whole thing of boundary layers of air over cars does weird things to airflow...we used to all love the pro stock `letterbox' style hoodscoops because they lifted the scoop out of the dead air layer - I think what you are experiencing here is a similar effect - the air against the upper part of the windscreen in a layer about 2 - 3 inches thick is effectively dead, with laminar flow over that (so the real `pressure ' we are all looking for is actually a couple of inches in some cases above the body...) maybe try the pressure reading experiment again but put your probe a few inches away from the body/glass surface - but I don't want to make you attract the police attention again!

This thing with pressure at the windscreen base can be a real good thing tho - years ago I saw a picture of a nascar engine bay and the aircleaner was sealed with a rubber diafraghm to the cowl under the windscreen (so, level with the air cleaner inside the engine bay) - I copied this in an XW falcon and it worked great - air is picked up from the cowl vents in front of the windscreen which pressurises the plenum chamber underneath it (which makes sense as this is what ford designed it to do in the first place, only to provide air for the cars heater/vent system...)

 

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 Post subject: Re: FIENDISHLY SIMPLE AIR PRESSURES OVER AN EF FAIRMONT HOOD
Posted: Tue Jun 16, 2009 1:07 pm 
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Yes --- I was giving a bit of helpful advice to one of the dirt track oval boys who is sticking a roll cage and working up an EF MONTY for doing the NZ series this coming season. They actually end up with no windscreen at all, but by putting a four inch pipe where the passengers face should be.... Well... Seems like an okay idea to me!

That pipe is going a big box with a pod filter in the middle of it which is then going to the original EF pipes turned upside down so they go through the firewall rather than forwards.

Interesting way of doing things, should work a treat. Pity the circuit racing only really gets to 100km/h in that class... With a setup like that at 200km/h you may find a little positive boost!
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 Post subject: Re: FIENDISHLY SIMPLE AIR PRESSURES OVER AN EF FAIRMONT HOOD
Posted: Tue Jun 16, 2009 1:32 pm 
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Wicked, I always thought those backward facing scoops were to drag air out of the engine bay, ie through the radiator and out over the car, learn something new every day!

 

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 Post subject: Re: FIENDISHLY SIMPLE AIR PRESSURES OVER AN EF FAIRMONT HOOD
Posted: Tue Jun 16, 2009 1:45 pm 
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with rearward facing scoops they do let hot air out below I dunno maybe 20 kp/h but after that its all pressure going inward... if you have an older ford put your vents on fresh air and go for a drive, you'll feel air pressure above about 15 k's

Oh, and also, Fiend, your idea with picking up air in the interior works because there are two advantages we're looking for - pressure is great if you can get it obviously, but cooler air is also a huge benefit - the interior air's gotta be cooler than the engine bay...

 

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 Post subject: Re: FIENDISHLY SIMPLE AIR PRESSURES OVER AN EF FAIRMONT HOOD
Posted: Tue Jun 16, 2009 1:59 pm 
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I feel that very pressure in my EA! it bloody hisses in!

 

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 Post subject: Re: FIENDISHLY SIMPLE AIR PRESSURES OVER AN EF FAIRMONT HOOD
Posted: Tue Jun 16, 2009 2:02 pm 
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there you go - if you can feel/hear it at road speeds, imagine how much free air pressure there is at nascar speeds !! bottom line is, its cold, and its under pressure...

 

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 Post subject: Re: FIENDISHLY SIMPLE AIR PRESSURES OVER AN EF FAIRMONT HOOD
Posted: Tue Jun 16, 2009 2:13 pm 
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This reminds me of an article done a while back at autospeed. They plumbed the intake of a Mazda MX5 to the cowl below the windscreen.
It gave me ideas ever since I read it.

http://autospeed.com/cms/title_FreeFlow ... ticle.html

 

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 Post subject: Re: FIENDISHLY SIMPLE AIR PRESSURES OVER AN EF FAIRMONT HOOD
Posted: Tue Jun 16, 2009 2:25 pm 
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yep, well I can confirm, it definately works...I'm a big believer in cold air intakes - when you've fitted one, go for a drive on a cold rainy night....the denser moisture laden air does amazing things power and torque wise, very noticeable...It always amazes me how many cars you see in magazines and shows etc that have had huge dollars spent chasing hp, then have a smallish open element air cleaner sucking hot underhood air....when there's free horsepower literally flowing all over the car!!! I've even tried using 3 or 4 inch flexy hose from under the front bumper, worked well...

 

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 Post subject: Re: FIENDISHLY SIMPLE AIR PRESSURES OVER AN EF FAIRMONT HOOD
Posted: Tue Jun 16, 2009 5:15 pm 
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NZEA wrote:
Wicked, I always thought those backward facing scoops were to drag air out of the engine bay, ie through the radiator and out over the car, learn something new every day!


MATE - How many times have I talked to you about this stuff?

No one listens, sigh....


And I repeat - I was doing all this to find VENT positions originally, so INTAKE was slightly outside the scope.

Once again, I show you what I invented for the intake...

Image

Anyways, all good. Intake works well for providing ample cold air with no restriction to the "suck" of the engine. There is no positive boost provided tho, but this system could possibly be boxed in entirely around pod if I felt that way inclined.


In the dirt trackers there is no glass in any of the windows, so you get kind of a tunnel of air flow through the front of the car and out the back... I think putting a four inch pipe right where the passengers face would have been is a pretty good idea... Either that or put it a few inches above the roof - but that would start to look real odd for a "production car".
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 Post subject: Re: FIENDISHLY SIMPLE AIR PRESSURES OVER AN EF FAIRMONT HOOD
Posted: Tue Jun 16, 2009 5:28 pm 
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Hi Fiend, I reckon you are on a good thing there but with one change - by all means, the intake side is good - the `exit' though, I reckon, will happen through the rear lower end of the engine bay along with the radiator air - as discussed, you'll actually have air coming IN at windscreen base at speed...

 

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 Post subject: Re: FIENDISHLY SIMPLE AIR PRESSURES OVER AN EF FAIRMONT HOOD
Posted: Tue Jun 16, 2009 5:35 pm 
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Yeahp. You're right. I have actually chopped bloody great holes in my bonnet about as third of the way from the front to the rear... They work real good for helping out the radiator and work in conjunction with the phenolic spacer I designed and installed between the head and the BBM.

Stops all the hot air from the radiator going the whole way down the BBM and out the back of the engine bay you see....

Image

They appear higher in the photos, but they do let air out well... No positive pressure anywhere near the outside of these puppies...

Image
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 Post subject: Re: FIENDISHLY SIMPLE AIR PRESSURES OVER AN EF FAIRMONT HOOD
Posted: Tue Jun 16, 2009 5:46 pm 
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Excellent - way to go...I've often (during summer at least ) thought about an exit in the bonnet behind the radiator line to help air flow... mines a 351 in an XB coupe and I don't want to chop up its current bonnet as it has GT scoops but I do have the original `non scooped' bonnet in the shed, was thinking about going crazy on that... the other thing I was thinking was, as my aircleaner sits right at the rear passenger side of the engine bay (cos of LPG setup) is doing a NACA style duct (as on XAGT's) but about 2/3rds of the way back on passenger side of the bonnet, so it literally dumps right into the air cleaner (similar I suppose to how some 260 - 280 Z datsuns were set up, I think for turbo models - other alternative is to do a shaker but with underbonnet ducting to aim its air into this offset air cleaner setup..

 

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 Post subject: Re: FIENDISHLY SIMPLE AIR PRESSURES OVER AN EF FAIRMONT HOOD
Posted: Wed Jun 17, 2009 2:52 pm 
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I bloody listen...most of the time...

Now I looked at the rain on my bonnet on way home yesterday and you know what? It was barely moving at 100! There ya go!

 

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