lov-2-rev

iTrader: (87)

I would like to know about high and low pressure points on the front of our FC's. Now, I know that the nose is a high pressure point(obviously), and I assume that the area around the scoop of a TII is also a high point.

What about the cowl and windshield areas though?

I am looking to install some small heat extractors in my hood up by the cowl.
Will this be a lower pressure zone then the front bumper?
And if so, is it enough of a difference to move some decent air volume from the engine bay?

DoriFCto

Here you go...

https://www.rx7club.com/showthread.p...light=pressure

hope that helps!!!!!

jgrewe

iTrader: (1)

The base of the windshield is usually a high pressure area but how high depends on the angle of the windshield. Remember cowl induction hoods on the old Chevys. Without getting out my magnahelic guage I would guess the middle of the hood or close around the edge of the IC scoop would be a low pressure area. Something just behind the radiator and in front of the IC scoop would be best but then you would be venting right in front of the IC.
It looks like you need to go with a FMIC! So if you've been looking for an excuse for that upgrade, there you go.

Edit: cool picture, gonna bookmark that one!

lov-2-rev

iTrader: (87)

Thanks for the info guys. That diagram is very informative.
However, I should explain my situation fully. I have a FMIC with a large front bumper opening and an N/A hood. Also, I have a rad panel and am fabricating a bumper undertray. All in the name of air flow through the rad and IC. I was using the TII scoop as a reference point.

If I were to make an assumption based on the diagram alone, I would say that the air at the stock IC would be flowing outward. But this isn't right. The air moves inward, correct? This adds another element into the equation. Air flow.
I guess what I'm getting at is this; Will the high pressure point at the front bumper, combined with the air flow across the hood, allow for the heat in the engine compartment to vent out near the cowl?

jgrewe-- I agree with your conclusion that a vent in the front to middle of the hood is ideal. I personally dislike the large vented V-mount style hoods on the market. I am looking to make something functional and much more discreet.

jgrewe

iTrader: (1)

I think you're getting into some experimenting at this point. The diagram gives you the best info to start with. The reason you have low pressure at the front end of the hood is from the air bouncing off the nose and from the velocity of the air going over the hood compared what is going on under the hood. Bernouli's principle at work, velocity increase=pressure decrease.

I wonder if the wheel wells are high or low pressure? Maybe vent out there above the frame in front of the strut towers.

If you are serious about making this functional and not for show I'd recommend buying a magnehelic guage and some rubber hose and start testing areas for pressure. A good one that goes + or - 15 inches of water is about $75. I got mine from Graingers. Put one end of the hose where you think will neg pressure and drive around. Keep the end of the tube at a right angle to suspected air flow so you don't just get 'ram air effect' showing up.

91verty

YOu guys have way too much time on your hands! LOL

Rotary Noob

Yeah, but when their car looks awesome, is functional, and doesnt look like someone drove through a "rice" field with it, youll be saying that its cool. Not to try and bag on you or flame you, but thats what will happen.

As for what youre doing, I would like to do the same thing, look forward to hearing about what you figure out!

drago86

Just make a water manometer and start testing.

RETed

No, it will not vent near the cowl.

In fact, old-school V8's used to use a "cowl induction" hood which caused the airflow to go in at the base of the hood and enter the engine bay from the rear.


-Ted

Black91n/a

From seeing a pressure plot of a NASCAR in CFD, the wheel wells are probably at higher pressure, so that'd be a less than ideal place to vent. You could vent from behind the opening with a hole in the fender.

jgrewe

iTrader: (1)

Been reading Racecar Engineering again havn't you...

BLUE TII

iTrader: (9)

I wonder if the wheel wells are high or low pressure? Maybe vent out there above the frame in front of the strut towers.

The front wheel wells are a low pressure area due to the blister fender shape and the careful shaping at the trailing edge of the wheel well.

You can observe this by watching an FC in the rain- waterspray exits the front wheel wells.

Mazda used this low pressure area as well as the TII wheels integral turbine to cool the brakes along with introducing airflow to the wheel well via the brake duct.

Much attention was paid to aerodynamic details on the FC- even the strut tower sheetmetal was shaped to increase airflow out of the engine bay.

If I were to make an assumption based on the diagram alone, I would say that the air at the stock IC would be flowing outward. But this isn't right. The air moves inward, correct? This adds another element into the equation. Air flow.

Right, because the airflow in the low pressure area of the hoodscoop has such high velocity and under the car is also low pressure air flows through the IC the correct direction at speed.


jgrewe-- I agree with your conclusion that a vent in the front to middle of the hood is ideal. I personally dislike the large vented V-mount style hoods on the market. I am looking to make something functional and much more discreet.

I believe venting as far forward as possible on the hood is best to take advantage of the "bow wave". I agree it doesn't look as good to the untrained eye. Putting the vent at the front of the hood also lets water entering the vent exit without getting on electrical components though.


If you want to see if a vent in the cowl area will help cooling you can put spacers on your hood hinges so the rear is canted up and creates a gap.

Black91n/a

Yep. I buy it whenever I can, but not a lot of places carry it and I move around too much for school and co-op work that subscribing isn't an option really.

Free articles:

http://www.advantage-cfd.co.uk/News/...-Releases.html

EDIT: Air/water flowing out indicates HIGH pressure in the wheel well, not low. Agreed on the hoodscoop thing, you can get flow inwards at a low pressure spot with the use of a scoop, and it depends on the pressure on the other side, not just the relation to ambiant.

Most race cars and OEM fender vents are behind the wheel opening, not in it.

Kyrasis6

A very simple and easy method is to tape a crap load of little streamers in places then drive the car. Places where the streamers lay down flat will be high velocity areas, places where the streamers fly around will be turbulent areas.

You also don't want to vent into a place with low pressure under the car as it will decrease downforce. My chassis book says venting to the wheel wells is a good place because it is a fairly neutral spot which shouldn't effect downforce. I find it hard to believe that the wheel wells would have a high pressure, air from below the car doesn't really get up in there and any air from the sides is directed around by the wheels and tires. If you don't believe it watch the next NASCAR short track race like at Martinsville or Bristol, I garantee if you watch close enough you will see crap loads of brake dust fall off and when the tire changers hit the lug nuts crap will go flying everywhere.

I don't trust much information in magazines, even a race oriented one, they are still written by editors who often have little or no experience and are simply translating information given to them. I've seen tech articles in magazines where the information came from our shop and was translated in a way which gave wrong or decieving information. Furthermore a compedative team is not going to disclose confidential information and may just give the interviewer some results from some random test which worked out horrible and then they hype it up to make it sound good.

Edit: The last 3 or 4 posts where written while I was writing this post.

Black91n/a

This is from the Racecar Engineering site about the author of the articles:

Simon Mcbeath

Simon entered motorsport journalism in 1993, writing for the late "CCC" magazine. Previously a technical manager in the manufacturing sector, he began writing for Racecar Engineering in 1997.
He graduated from Southampton University with a scientific background and, as well as being the author of several technical motorsport books, Simon also set up his own company, The Wing Shop Ltd, in 2003, specialising in the manufacture of carbon composite racecar wings.

He has been an amateur competitor in motorsport for over 25 years and has scored wins on every UK mainland hill as a competitive speed hill climb driver. He has driven a number of cars in various speed events and magazine tests including ex-F1 engined single seaters. He has also taken part in preparing and developing a number of single seaters over the years, with a special interest in aerodynamics.

Simon is currently also working as an instructor at the Gurston Down Hillclimb Drivers school as well as being their press officer during motorsport season.



I'd say he'd know what he's talking about, or they wouldn't publish it, and Advantage CFD wouldn't put it up on their site. I do beleive he does all the analysis himself. That said, CFD isn't perfect, it's a suppliment to the wind tunnel, not a substitute.

The wheel only partially blocks the opening, there's a big scoop in effect there, catching the air in the back of the fender, causing a high pressure area. Ever wonder why the Insight has covered rear fenders? It's to reduce the pressure drag associated with the wheel opening and to keep smoother airflow over that area of the car.

RETed

Did someone just dis RCE mag?



-Ted

lov-2-rev

iTrader: (87)

LOL. I know all about "old-school V8's" I have 3 cowl induction vehicles. However, the most aerodynamic of them has a windshield angle of approx 48 deg. I was hoping the much more reclined windshield on a FC would aid in reducing turbulance at the cowl. I guess not enough.
I believe you are mistaken. The front wheel wells are high pressure points. This is an area where air is being forcefully induced via brake ducts and undercar turbulance. The area BEHIND the wheel wells are low pressure points. It is a common area for engine-bay venting used on many vehicles from the factory.

Regardless, I have no intention of doing vented fenders.
I believe this is the easiest way to run this experement. Short of straping six feet of hose to my hood. In all actuality, I don't need a precise reading as in a magnahelic gauge or other device, I simply need to have a positive or negative result.

Besides, my wife is a 7th grade science teacher. I can probably earn some brownie-points if I get the sience club kids involved. hehe
I think so Ted. Let the virtual bitch-slapping begin.
By the way, I love your ever changing avitar!

Kyrasis6

My post said nothing aimed at RCE, neither did it say all magazines, just making a generalization that there are a lot of magazines out there that are full of crap and that just because it is written in a magazine doesn't mean it is nessesarily true.

I would definatly say Black91n/a post proves the editor's credability in this case.

Black91n/a

Yea, I'd trust just about anything that Racecar Engineering publishes. Race Tech is also pretty good.

BLUE TII

iTrader: (9)

I believe you are mistaken. The front wheel wells are high pressure points. This is an area where air is being forcefully induced via brake ducts and undercar turbulance. The area BEHIND the wheel wells are low pressure points. It is a common area for engine-bay venting used on many vehicles from the factory.

Yeah, I was thinking of a surface model like the linked FC aerodynamic profile where the surface of the wheel well opening is a relative low pressure area venting the wheel wells.

In a 3d model of the volume of the wheel well that volume would indeed be a higher pressure area as it has a high pressure brake duct and the air is increased in volume by brake heat.

If you wanted to vent the engine bay through the wheel well I guess the best way would be to run a duct (hose) from the engine bay to behind the front wheel flush w/ the fender surface (like the Boneville FC exhaust). Otherwise you would have to depend on the wheel well area being lower pressure than the engine bay.

Still, the front of the hood is probably best from an aerodynamic drag perspective as well as adding air mass to the flow over the high pressure areas at the cowl and tail adding downforce.

Also, you have the high pressure of the hot air exiting the radiator right there at the low pressure area in the hood so ducting efficiency is not as critical.

I know the front hood vent doesn't look subtle or OEM (that is why my H-mount IC set up doesn't have the vent), but you could check out pics of cars that did have the vent here OEM to find ways to make it look better. The 4 rotor Mercedes C-111 and Mazda's own
MX-03 3 rotor concept cars spring to mind.