I am curious about what are the highest and lowest pressure
areas on the surface of a rolling F-body.

I would like to put the air inlet tube at the highest and dump the
cutout at the lowest.

I have never seen any real info on this.

 

Well if I remember and apply Bernoulli’s equation correctly then the movement of air around your car is constantly changing in both magnitude and direction. Free fluids move in the direction of the lowest pressure area. So an increase in velocity means that the fluid is moving from a high pressure region to a low pressure region and a decrease in velocity means that the fluid is moving from a lower pressure region to a higher pressure region. Now we have to look at the shape of the car and figure out how the air is moving around it. Check out the diagram of the Third Gen Camaro and notice the airflow pattern. The vorticies (curly lines) indicate areas where the laminar flow (smooth straight lines) break down. Ok, the air in front of the car hits the nose and since we are at subsonic speeds it won't compress in volume so it has to move over and around the car's surface. Since the car's cross-sectional area is changing the air is forced to accelerate as it moves over the nose and windshield of the car and then decelerates down the rear deck lid and over the bumper. This indicates that the roof of the car has a lower pressure than the front bumper or the rear bumper. (velocity = distance * time)-(for two particles to travel different distances in the same amount of time the velocities must be different so the faster particle is being accelerated towards the low pressure area). So here would would say that the highest pressure is at the nose or tail and lowest above the roof but there is phenomena to consider and that is the flow separation that occurs at the back decklid area (notice the swirly lines in the diagram) Here the the flow around the car went through a massive acceleration because of the void that was left by the car moving out of that space. Something has to fill this vacuum and Bernuouli says the air will fill it but it can't fill it fast enough so you get a negative pressure gradient moving into this region. This lower pressure region is sucking the car backwards. The faster you go the more powerful this suction becomes. As you move from the decklid down to the pavement the the pressure goes from higher to lower to higher at the street due to the air moving under the car.

Best place for an intake: at the base of your windshield (Ever wonder why the climate control systems intake is located here?) I'm not an aerodynamic guru but I don't think the pointed noses on these cars allow enough pressure to build up in font of the bumper to be useful. It has to do with the small distance the air has to travel to get "around" this region. But then at the base of the window you are now moving a lot more air out of the way and this region is still far enough away from the roof for the pressure to be greatest (once you get to the roof the air slows its acceleration.

Best place for exhaust: on the top side of the bumper. You'll want to find the "sweet-spot" here. The good thing is that the faster you drive the bigger and more powerful this sweet spot becomes.

Last thing to consider: What kind of head losses or gains are you going to get by routing extra plumbing to these optimum areas?

 

Hell, well this explains "cowl induction", thanks.

forgive my igonorace but does this apply to the 4th gen body?
the pic shows the 3rd gen.

 

Squealing, you're kinda right.
But a lot wrong too.

Simply put, if you have an intake there, there is no possible way for it to be the same spot as there is maximum pressure.

Maximum pressure occurs only at what's called a Stagnation point. which is the point at which the flow across two areas of a car separates. think of it as the point of a knife that's cutting through the air. the very edge of the blade has the most pressure on it.

to get the most out of an intake, you would place it in front of a high-drag area, to eliminate the drag at that point, and use it effectively.

The base of the window generates a vortex that spins air forward along part of the hood and creates lots of drag. that's why cowled induction helps so much. but to get maximum performance from an intake, put it at the base of the bumper and put a solid or mostly solid grille on the nose.

exhaust pipes are in the correct location to provide a negative pressure from the slipstream behind the car from the air below it.
the area above the trunk lid is extremely turbulent and has no positive flow characteristics, so that is a bad choice for anything, including exhaust.

honestly, an SS-style hood is very effective, because it scoops air from the hood all the way up to the ram intake, which is also pulling it in, so it doesn't create any drag either.

just an Aerospace Engineering student's .02

 

??base of bumper would be where the air dam is??

would the solid grille on the front be to gain front downforce, and help the car turn?

 

I've been in the Aerodyn 2 tunnel for testing and you'll want to put the air intake in the bumper...right around the level the licence plate would be. The Cowl isn't bad, but you only want the engine breathing from there. The hood and the base of the windshield need to be sealed from each other to keep positive pressure from building up under the front of the car. Do a search for " CFD racing car" in Google images, you're going to want to put the intake in an area that looks "red". The exhaust in places that are blue. You can also find some neat stuff in youtube that will help you visualize what's going on. Hitting windtunnel, aerodyn2, etc... in your searches leads to you more

I agree with the slipstream assessment of the exhaust. The area that the air that moves the fastest has the lowest pressure. It would need to be below floor level...which is possibly going to cause clearance issues.

 

 

Your right. How about a prostock hood scoop. Acts as a diffuser to slow the oncoming air and increase the pressure. Wonder if that the pressure inside the scoop is higher than in front of the bumper.

 

[QUOTE=briannutter;9579636]I've been in the Aerodyn 2 tunnel for testing and you'll want to put the air intake in the bumper...right around the level the licence plate would be. [QUOTE]

like this


http://i2.photobucket.com/albums/y11...n/IMG_0056.jpg
http://i2.photobucket.com/albums/y11...n/IMG_0057.jpg

 

how did u do that mod do you have any other pics iv never seen that before

 

W.J. won't be moving his air intake any time soon just due to the height of the intake manifold. If he could miraculously do the bumper thing...he would. The front plate area has a much larger "sweet spot". The opening can be moved a couple feet left or right, but the leading edge of the car stalls the air the most. Where velocity is the highest, the pressure is the lowest.

 

[QUOTE=studderin;9614587][QUOTE=briannutter;9579636]I've been in the Aerodyn 2 tunnel for testing and you'll want to put the air intake in the bumper...right around the level the licence plate would be.
You should rig up a pressure transducer inside your airbox then record the data as you slow from about 140mph in neutral or turn the engine off (that could be dangerous though)

 

Hmmm, so say on a pontiac f-body would the ideal sweet spot for the intake be exactly where the front license plate cover is? If this were to be cut out like alot of the turbo guys do, and sealed to a intake the ran straight up and over the cowl into the location of the stock intake ducting would this be ideal? Or even possibly cutting the cowl to give the air a more direct approach?

I see the sawzall coming out!

I don't see any better way to do it as long as you kept the bend over the cowl sufficient enough that it would'nt become a restriction.

Thoughts?

 

 

 

I think you're talking about the core support. yep, you're right about the radiator being right in the way. some companies make "airbridges" where the flat oval area over the core and radiator matches that of some 3" ducting. The LT1 pontiacs were more pointy and they had the openings in the front bumper to the left or right of the plate. Those aren't bad, but not quite as effective as the plate area (as that would have the highest stall). The nostrils on the hood aren't so great at all...even compared to a cowl induction...once the air makes it over licence plate area (say a few inches above it) a smoke stream would RAPIDLY become apparent because of the velocity....and this means lower pressure. the same smoke stream hitting the licence plate will be seem as balooning out and dissapating in equal directions. I cut a hole behind my licence plate for track days on my LT1 Vette. I just pull the plate on those days for a bit more fresh air. I don't think I'm getting a lot more power or anything, but it seems like every little bit should help.

 

LOL yea, I meant the cowl. I was thinking a long time ago of make a box to match the area of the cut out license plate hole and then running that straight up to the direction of the core support (I just tried to type cowl again!).

Mind you, I have no bumper support or ac system or anything, so cutting my core (for a straighter shot to the intake), removing my factory lower air box, and zip tieing the radiator forward would be alot easier than working with all the factory systems in there.

 

jimmy, the under body is a huge trap for air. you would have to do a lot of covering/smoothing to get it to do anything.

 

The stock SS hood air inlet is too far back to be in a high pressure area. Actually, it's in a low pressure area. The WS6 hood is closer to being in a high pressure area. In testing at 150+ mph speeds between my Trans Am and my buddy's Z28, we found by logging manifold pressure that a sealed Fast Toys Ram air (that grabs high pressure air from the front spoiler) made 2 KPa more than my sealed WS6 hood. Both made positive KPa above 150mph (in standing mile competitions). The sealed WS6 hood made 3 KPa of boost and the Fast Toys ram air system made 5 KPa of boost. Plus, the "Catfish" was much more aerodynamic with a flat hood than the WS6. The WS6 hood is pretty dirty aerodynamically and the airbrake it creates is not worth the boost it makes at high speed when you can make more with a cleaner setup.

 

Patrick, by boost do you actually mean positive pressure beyond BARO? Most intakes i've tested have drops of MAP on high rpm, so i'm very interested to see if the boost was purely speed related, or a result of a good design.