C3 Aerodynamics: Ventilation & Induction Airflow
06-18-2006, 01:44 AM
#61
Burning Brakes
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Rich,
I was just settin' out in the garage lookin' at the car, thinkin'.... I don't know that a manometer would work under the conditions we could test with. Yes it measures pressure differential, but it would need to be a static atmosphere (I'm thinking of the liquid filled style I used to use in HVAC work). Seems to me that in the "violent" atmosphere surrounding a vehicle in motion, the readings would not have much consistancy or integrity. (And probably just blow the liqiud all over the cabin.) If the orifice was pointed into the airstream it would give a high reading, and if perpendicular or away from the airstream, a low reading due to air velocity. Also you would have to have readings from a neutral area and an area outside the "teardrop" to get any true differentials. By the time I was done imagining all this, my car looked like a porcupine with tubes sticking up and out from flush to 18" high with little breather-type air filters on them.....Even inside the engine bay the turbulance would overwhelm the readings...I think the yarn trick (or smoke bombs) gives us as much information as we can hope to get in field experiments.
That, books, and the combined brain power of the almighty Corvette Forum.
John
I was just settin' out in the garage lookin' at the car, thinkin'.... I don't know that a manometer would work under the conditions we could test with. Yes it measures pressure differential, but it would need to be a static atmosphere (I'm thinking of the liquid filled style I used to use in HVAC work). Seems to me that in the "violent" atmosphere surrounding a vehicle in motion, the readings would not have much consistancy or integrity. (And probably just blow the liqiud all over the cabin.) If the orifice was pointed into the airstream it would give a high reading, and if perpendicular or away from the airstream, a low reading due to air velocity. Also you would have to have readings from a neutral area and an area outside the "teardrop" to get any true differentials. By the time I was done imagining all this, my car looked like a porcupine with tubes sticking up and out from flush to 18" high with little breather-type air filters on them.....Even inside the engine bay the turbulance would overwhelm the readings...I think the yarn trick (or smoke bombs) gives us as much information as we can hope to get in field experiments.
That, books, and the combined brain power of the almighty Corvette Forum.
John
06-18-2006, 04:15 AM
#62
Magnehelic is the trade name for the frictionless gauge movement of Dwyer pressure gauges. They are widely used form scuba gear to indicators for air filter condition.
They are just pressure gauges, perfect for stuff like setting up carb air flow or measuring cowl induction pressure
They are just pressure gauges, perfect for stuff like setting up carb air flow or measuring cowl induction pressure
06-18-2006, 09:48 AM
#64
Originally Posted by JPhil
Rich,
I was just settin' out in the garage lookin' at the car, thinkin'.... I don't know that a manometer would work under the conditions we could test with. Yes it measures pressure differential, but it would need to be a static atmosphere (I'm thinking of the liquid filled style I used to use in HVAC work). Seems to me that in the "violent" atmosphere surrounding a vehicle in motion, the readings would not have much consistancy or integrity. (And probably just blow the liqiud all over the cabin.) If the orifice was pointed into the airstream it would give a high reading, and if perpendicular or away from the airstream, a low reading due to air velocity. Also you would have to have readings from a neutral area and an area outside the "teardrop" to get any true differentials. By the time I was done imagining all this, my car looked like a porcupine with tubes sticking up and out from flush to 18" high with little breather-type air filters on them.....Even inside the engine bay the turbulance would overwhelm the readings...I think the yarn trick (or smoke bombs) gives us as much information as we can hope to get in field experiments.
That, books, and the combined brain power of the almighty Corvette Forum.
John
I was just settin' out in the garage lookin' at the car, thinkin'.... I don't know that a manometer would work under the conditions we could test with. Yes it measures pressure differential, but it would need to be a static atmosphere (I'm thinking of the liquid filled style I used to use in HVAC work). Seems to me that in the "violent" atmosphere surrounding a vehicle in motion, the readings would not have much consistancy or integrity. (And probably just blow the liqiud all over the cabin.) If the orifice was pointed into the airstream it would give a high reading, and if perpendicular or away from the airstream, a low reading due to air velocity. Also you would have to have readings from a neutral area and an area outside the "teardrop" to get any true differentials. By the time I was done imagining all this, my car looked like a porcupine with tubes sticking up and out from flush to 18" high with little breather-type air filters on them.....Even inside the engine bay the turbulance would overwhelm the readings...I think the yarn trick (or smoke bombs) gives us as much information as we can hope to get in field experiments.
That, books, and the combined brain power of the almighty Corvette Forum.
John
When I used to own a new 69 Roadrunner,the hood would "ripple" at 110 mph...I always attributed it to the thin metal of the hood...now I'm thinking it was pressure due to speed...at least our vettes have functional side vents to relieve some of this pressure..
John..think of your knowledge of ventilation...if you have a fan supplying air,you must also exhaust the air to maintain the exchange,otherwise you create to much positive pressure...I think..
Rich
Last edited by rihwoods; 06-18-2006 at 09:52 AM.
06-18-2006, 10:21 AM
#65
Le Mans Master
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St. Jude Donor '07
Why wouldn't the side vents do the same thing as the cowl vents? Seem like the same logic applys there to. Do you think the side vents start vacuuming in air as speeds above 70 mph? Maybe the air moving past the wheel wells causes a disturbance of air flow and the vents can then exhaust air.
Here is another question. Do you think removing those rubber splash guard over the a-arms would releave pressure? Mine seem to always be pushed in.
Here is another question. Do you think removing those rubber splash guard over the a-arms would releave pressure? Mine seem to always be pushed in.
06-18-2006, 10:34 AM
#66
Originally Posted by Budman78
Why wouldn't the side vents do the same thing as the cowl vents? Seem like the same logic applys there to. Do you think the side vents start vacuuming in air as speeds above 70 mph? Maybe the air moving past the wheel wells causes a disturbance of air flow and the vents can then exhaust air.
Here is another question. Do you think removing those rubber splash guard over the a-arms would releave pressure? Mine seem to always be pushed in.
Here is another question. Do you think removing those rubber splash guard over the a-arms would releave pressure? Mine seem to always be pushed in.
All I know is those splash guards just lie there...mine are folded back..
Rich
Last edited by rihwoods; 06-20-2006 at 01:03 AM.
06-18-2006, 10:41 AM
#67
Le Mans Master
Good Discussion.
I've been thinking and experimenting on this topic for several years with my 71 SB vert.
I did the tuft test up to 80 with a BB hood and did not see the negative pressure at the base of the windshield shown above. maybe the raised portion of the L-88 hood enahnces this negative pressure? So I decided to try to pick up cold air from the front of the radiator ala C4,C5,C6.
Late C3s did this with a goofy looking combination of plastic ducts and hoses feeding a round air cleaner. So, GM thought it was a good idea.
For my tpi 383, I'm fabbing up a fiberglass air box that looks like a large dust pan. The lip extends over the top of the radiator fame and the back mounts on the throttle body with the ar cleaner inside the scoop. With a BB hood, there is plenty of room to capture enough cold air coming up over the face of the radiator to satisfy the 383. I've tried a prototype and it works great. Remember, a 10 degree drop in inlet air temp is worth 1% increase in HP. Here in Texas in August, the temp diff is easily 100 degrees so that means a 10% increase in HP. In my case that's almost 40 HP! It's even more in what we call winter.
RE: air pressures and engine bay temps. In an effort to control engine bay temps (383, coated headers), I relocated everything that was blocking the side vents and added open louvers to the top of the BB hood ala the false louvers on the 57 Vette. I verified with remote sensing thermometer that all these vents are doing their job.
I looked at opening up the false vents on the BB hood but they are in front of the radiator and, while they would release some lifting pressure at very high speed, the opening at this location would also reduce whatever ram air pressure I have forcing air into my scoop.
Up front, I am using a modifed Pace Car spoiler. I don't care for the side extensions that push air around the front tires (they just don't look right on a chrome bumper C3) so I cut them off and am using the center portion only. I think this scoops up the air and directs it up the bottom feed air inlets. Hard to verify this.
I also have removed the front license plate to get more air to the radiator front in hopes of increasing ram air pressure to the scoop.
I've been thinking and experimenting on this topic for several years with my 71 SB vert.
I did the tuft test up to 80 with a BB hood and did not see the negative pressure at the base of the windshield shown above. maybe the raised portion of the L-88 hood enahnces this negative pressure? So I decided to try to pick up cold air from the front of the radiator ala C4,C5,C6.
Late C3s did this with a goofy looking combination of plastic ducts and hoses feeding a round air cleaner. So, GM thought it was a good idea.
For my tpi 383, I'm fabbing up a fiberglass air box that looks like a large dust pan. The lip extends over the top of the radiator fame and the back mounts on the throttle body with the ar cleaner inside the scoop. With a BB hood, there is plenty of room to capture enough cold air coming up over the face of the radiator to satisfy the 383. I've tried a prototype and it works great. Remember, a 10 degree drop in inlet air temp is worth 1% increase in HP. Here in Texas in August, the temp diff is easily 100 degrees so that means a 10% increase in HP. In my case that's almost 40 HP! It's even more in what we call winter.
RE: air pressures and engine bay temps. In an effort to control engine bay temps (383, coated headers), I relocated everything that was blocking the side vents and added open louvers to the top of the BB hood ala the false louvers on the 57 Vette. I verified with remote sensing thermometer that all these vents are doing their job.
I looked at opening up the false vents on the BB hood but they are in front of the radiator and, while they would release some lifting pressure at very high speed, the opening at this location would also reduce whatever ram air pressure I have forcing air into my scoop.
Up front, I am using a modifed Pace Car spoiler. I don't care for the side extensions that push air around the front tires (they just don't look right on a chrome bumper C3) so I cut them off and am using the center portion only. I think this scoops up the air and directs it up the bottom feed air inlets. Hard to verify this.
I also have removed the front license plate to get more air to the radiator front in hopes of increasing ram air pressure to the scoop.
06-18-2006, 11:00 AM
#68
The thermometer is a good idea...(wonder if I can shoot my Raytek mini temp gun thru the windshield to get temps at cowl opening..???) hee hee..think I'll just tape a thermometer just inside to see what I get...
Last edited by rihwoods; 06-18-2006 at 11:02 AM.
06-18-2006, 12:42 PM
#69
Burning Brakes
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In typical forced air HVAC systems, you figure twice the area for return air as for supply air. If you need 100 square inches of duct for adequate supply (pressurized) air flow, then you want 200 square inches for adequate return (non- or low-pressure) air flow to keep a good balance and efficiency of the system. Our "supply" air is the pressured up engine bay, the "return" would be our vents & other openings to relieve the pressure. Obviously we'll never get 200%, but on the other hand we're not dealing with a closed recirculating system either.
The side vents, as extraction vents, suck air by the principle of the venturi. If you were to place an obstruction immediatly behind the side vents(outside,on the exterior of the car), at a certain speed the pressure differential would overcome the venturi effect and it would reverse flow, just as the cowl scoop does. If your cowl scoop is open to the engine bay, as opposed to having a sealed plenum to the carb intake, it does have to overcome engine bay pressure before it will start sucking in. With adequate exhaust vents from bay, this bay pressure is reduced sooner, thus cowl induction begins at lower speeds.
Also, it is not as critical that there be a clear unobstructed flow path inside the side vents: we are drawing random, undircted air to an orifice via suction as opposed to pressure. An obstruction in pressurized air will destroy flow, but not so much in an open suction flow. Picture your bathtub: If you hold your hand under the spout as it's filling, you are obstructing the pressurized flow and it makes a mess. If you put your hand in front of the drain (not sealing it), it doesn't make much difference to the flow down the drain, it just goes around your hand and still drains at the same rate.
But, yes, I too want to delete the dryer and canister to open up that area and further reduce underhood clutter.
(Let me interject here, I am theorizing and thinking out loud through all this. I am no engineer, I'm just trying to use experience, book learning, discussion and what seems to me to be common sense to understand and use this. If anyone thinks I'm making a mistake somewhere, please speak up!)
Hmmmm #2....Got a friend who's into scuba diving...wonder if he's got a Dwyer guage he'd let me borrow.....
John
The side vents, as extraction vents, suck air by the principle of the venturi. If you were to place an obstruction immediatly behind the side vents(outside,on the exterior of the car), at a certain speed the pressure differential would overcome the venturi effect and it would reverse flow, just as the cowl scoop does. If your cowl scoop is open to the engine bay, as opposed to having a sealed plenum to the carb intake, it does have to overcome engine bay pressure before it will start sucking in. With adequate exhaust vents from bay, this bay pressure is reduced sooner, thus cowl induction begins at lower speeds.
Also, it is not as critical that there be a clear unobstructed flow path inside the side vents: we are drawing random, undircted air to an orifice via suction as opposed to pressure. An obstruction in pressurized air will destroy flow, but not so much in an open suction flow. Picture your bathtub: If you hold your hand under the spout as it's filling, you are obstructing the pressurized flow and it makes a mess. If you put your hand in front of the drain (not sealing it), it doesn't make much difference to the flow down the drain, it just goes around your hand and still drains at the same rate.
But, yes, I too want to delete the dryer and canister to open up that area and further reduce underhood clutter.
(Let me interject here, I am theorizing and thinking out loud through all this. I am no engineer, I'm just trying to use experience, book learning, discussion and what seems to me to be common sense to understand and use this. If anyone thinks I'm making a mistake somewhere, please speak up!)
Hmmmm #2....Got a friend who's into scuba diving...wonder if he's got a Dwyer guage he'd let me borrow.....
John
Last edited by JPhil; 06-18-2006 at 10:08 PM.
06-20-2006, 03:58 PM
#71
Safety Car
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I looked at the fender liners last night. No need to remove them. I can just cut a vent in the rear of them, and then the airflow has a straight shot from the wheel wells to the side vents. If you look into the side vents from the rear of the car, you are looking directly at the back of the fender liners.
06-20-2006, 04:18 PM
#72
Originally Posted by Bee Jay
I looked at the fender liners last night. No need to remove them. I can just cut a vent in the rear of them, and then the airflow has a straight shot from the wheel wells to the side vents. If you look into the side vents from the rear of the car, you are looking directly at the back of the fender liners.
Also want to check if yarn behaves same at cowl on 78....think it will...
Last edited by rihwoods; 06-20-2006 at 04:20 PM.
06-20-2006, 05:23 PM
#73
Racer
Originally Posted by Budman78
Here is another question. Do you think removing those rubber splash guard over the a-arms would releave pressure? Mine seem to always be pushed in.
06-21-2006, 01:16 AM
#74
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Originally Posted by flynhi
Good Discussion.
I've been thinking and experimenting on this topic for several years with my 71 SB vert.
I did the tuft test up to 80 with a BB hood and did not see the negative pressure at the base of the windshield shown above. maybe the raised portion of the L-88 hood enahnces this negative pressure? So I decided to try to pick up cold air from the front of the radiator ala C4,C5,C6.
Late C3s did this with a goofy looking combination of plastic ducts and hoses feeding a round air cleaner. So, GM thought it was a good idea.
For my tpi 383, I'm fabbing up a fiberglass air box that looks like a large dust pan. The lip extends over the top of the radiator fame and the back mounts on the throttle body with the ar cleaner inside the scoop. With a BB hood, there is plenty of room to capture enough cold air coming up over the face of the radiator to satisfy the 383. I've tried a prototype and it works great. Remember, a 10 degree drop in inlet air temp is worth 1% increase in HP. Here in Texas in August, the temp diff is easily 100 degrees so that means a 10% increase in HP. In my case that's almost 40 HP! It's even more in what we call winter.
RE: air pressures and engine bay temps. In an effort to control engine bay temps (383, coated headers), I relocated everything that was blocking the side vents and added open louvers to the top of the BB hood ala the false louvers on the 57 Vette. I verified with remote sensing thermometer that all these vents are doing their job.
I looked at opening up the false vents on the BB hood but they are in front of the radiator and, while they would release some lifting pressure at very high speed, the opening at this location would also reduce whatever ram air pressure I have forcing air into my scoop.
Up front, I am using a modifed Pace Car spoiler. I don't care for the side extensions that push air around the front tires (they just don't look right on a chrome bumper C3) so I cut them off and am using the center portion only. I think this scoops up the air and directs it up the bottom feed air inlets. Hard to verify this.
I also have removed the front license plate to get more air to the radiator front in hopes of increasing ram air pressure to the scoop.
I've been thinking and experimenting on this topic for several years with my 71 SB vert.
I did the tuft test up to 80 with a BB hood and did not see the negative pressure at the base of the windshield shown above. maybe the raised portion of the L-88 hood enahnces this negative pressure? So I decided to try to pick up cold air from the front of the radiator ala C4,C5,C6.
Late C3s did this with a goofy looking combination of plastic ducts and hoses feeding a round air cleaner. So, GM thought it was a good idea.
For my tpi 383, I'm fabbing up a fiberglass air box that looks like a large dust pan. The lip extends over the top of the radiator fame and the back mounts on the throttle body with the ar cleaner inside the scoop. With a BB hood, there is plenty of room to capture enough cold air coming up over the face of the radiator to satisfy the 383. I've tried a prototype and it works great. Remember, a 10 degree drop in inlet air temp is worth 1% increase in HP. Here in Texas in August, the temp diff is easily 100 degrees so that means a 10% increase in HP. In my case that's almost 40 HP! It's even more in what we call winter.
RE: air pressures and engine bay temps. In an effort to control engine bay temps (383, coated headers), I relocated everything that was blocking the side vents and added open louvers to the top of the BB hood ala the false louvers on the 57 Vette. I verified with remote sensing thermometer that all these vents are doing their job.
I looked at opening up the false vents on the BB hood but they are in front of the radiator and, while they would release some lifting pressure at very high speed, the opening at this location would also reduce whatever ram air pressure I have forcing air into my scoop.
Up front, I am using a modifed Pace Car spoiler. I don't care for the side extensions that push air around the front tires (they just don't look right on a chrome bumper C3) so I cut them off and am using the center portion only. I think this scoops up the air and directs it up the bottom feed air inlets. Hard to verify this.
I also have removed the front license plate to get more air to the radiator front in hopes of increasing ram air pressure to the scoop.
I was wondering what type pace car spoiler you are using.Is it the one piece fiberglass,or the three piece urethane?I also don't care much for the side tire sections.
06-21-2006, 06:34 AM
#75
Team Owner
Originally Posted by flynhi
Good Discussion.
I've been thinking and experimenting on this topic for several years with my 71 SB vert.
I did the tuft test up to 80 with a BB hood and did not see the negative pressure at the base of the windshield shown above. maybe the raised portion of the L-88 hood enahnces this negative pressure? So I decided to try to pick up cold air from the front of the radiator ala C4,C5,C6.
Late C3s did this with a goofy looking combination of plastic ducts and hoses feeding a round air cleaner. So, GM thought it was a good idea.
For my tpi 383, I'm fabbing up a fiberglass air box that looks like a large dust pan. The lip extends over the top of the radiator fame and the back mounts on the throttle body with the ar cleaner inside the scoop. With a BB hood, there is plenty of room to capture enough cold air coming up over the face of the radiator to satisfy the 383. I've tried a prototype and it works great. Remember, a 10 degree drop in inlet air temp is worth 1% increase in HP. Here in Texas in August, the temp diff is easily 100 degrees so that means a 10% increase in HP. In my case that's almost 40 HP! It's even more in what we call winter.
RE: air pressures and engine bay temps. In an effort to control engine bay temps (383, coated headers), I relocated everything that was blocking the side vents and added open louvers to the top of the BB hood ala the false louvers on the 57 Vette. I verified with remote sensing thermometer that all these vents are doing their job.
I looked at opening up the false vents on the BB hood but they are in front of the radiator and, while they would release some lifting pressure at very high speed, the opening at this location would also reduce whatever ram air pressure I have forcing air into my scoop.
Up front, I am using a modifed Pace Car spoiler. I don't care for the side extensions that push air around the front tires (they just don't look right on a chrome bumper C3) so I cut them off and am using the center portion only. I think this scoops up the air and directs it up the bottom feed air inlets. Hard to verify this.
I also have removed the front license plate to get more air to the radiator front in hopes of increasing ram air pressure to the scoop.
I've been thinking and experimenting on this topic for several years with my 71 SB vert.
I did the tuft test up to 80 with a BB hood and did not see the negative pressure at the base of the windshield shown above. maybe the raised portion of the L-88 hood enahnces this negative pressure? So I decided to try to pick up cold air from the front of the radiator ala C4,C5,C6.
Late C3s did this with a goofy looking combination of plastic ducts and hoses feeding a round air cleaner. So, GM thought it was a good idea.
For my tpi 383, I'm fabbing up a fiberglass air box that looks like a large dust pan. The lip extends over the top of the radiator fame and the back mounts on the throttle body with the ar cleaner inside the scoop. With a BB hood, there is plenty of room to capture enough cold air coming up over the face of the radiator to satisfy the 383. I've tried a prototype and it works great. Remember, a 10 degree drop in inlet air temp is worth 1% increase in HP. Here in Texas in August, the temp diff is easily 100 degrees so that means a 10% increase in HP. In my case that's almost 40 HP! It's even more in what we call winter.
RE: air pressures and engine bay temps. In an effort to control engine bay temps (383, coated headers), I relocated everything that was blocking the side vents and added open louvers to the top of the BB hood ala the false louvers on the 57 Vette. I verified with remote sensing thermometer that all these vents are doing their job.
I looked at opening up the false vents on the BB hood but they are in front of the radiator and, while they would release some lifting pressure at very high speed, the opening at this location would also reduce whatever ram air pressure I have forcing air into my scoop.
Up front, I am using a modifed Pace Car spoiler. I don't care for the side extensions that push air around the front tires (they just don't look right on a chrome bumper C3) so I cut them off and am using the center portion only. I think this scoops up the air and directs it up the bottom feed air inlets. Hard to verify this.
I also have removed the front license plate to get more air to the radiator front in hopes of increasing ram air pressure to the scoop.
06-21-2006, 10:00 AM
#76
Le Mans Master
BlackHorse:
I'm using a single piece Pace Car spoiler set just above curb height.
Comp,
I'm working on several AC related things right now. I'll try to post some pics in a couple of weeks when I finish.
W.
I'm using a single piece Pace Car spoiler set just above curb height.
Comp,
I'm working on several AC related things right now. I'll try to post some pics in a couple of weeks when I finish.
W.
06-21-2006, 09:11 PM
#77
Burning Brakes
This is all getting very interesting to me. I'm especially interested in the results of the A-arm flap tests. Mine are bad and in need of replacing, but if it turns out that the pros of having them missing outweigh the cons, I'll just remove mine and leave them out. I imagine they're there more for keeping rain/sleet/water/et cetera out of greased areas; though I could be wrong about that.
06-21-2006, 10:28 PM
#78
Racer
Who runs a stock lower baffle? The sheetmetal that fills in between the radiator support and front crossmember at the bottom of the car. It was missing on my 69 and I have never actualy seen one on a vette. Other than making it harder to work on does it have a positive or negative affect on front end lift or cooling? Any one have actual experience running with and without a lower baffle?
06-21-2006, 10:45 PM
#79
Originally Posted by MCMLXIX
Who runs a stock lower baffle? The sheetmetal that fills in between the radiator support and front crossmember at the bottom of the car. It was missing on my 69 and I have never actualy seen one on a vette. Other than making it harder to work on does it have a positive or negative affect on front end lift or cooling? Any one have actual experience running with and without a lower baffle?
The main issue with C3's is the fact that hoods have less free area over engines compared to other Chevorlet's so this means hotter air under the hoods of the C3 Corvettes...
06-21-2006, 10:53 PM
#80
Drifting
If someone can give me a 3d solid model or even 2d slices of the Corvette body I can run simulations in FIDAP (A Computational Fluid Dynamics Program) and get some nice contour plots of pressure and vector plots of flow at whatever speed and angle of incidence to the body you like...
Where it would get a bit sticky is the underside of the car to the ground.
I Just finished building a 256 processor Simulation System...
Just a thought
Where it would get a bit sticky is the underside of the car to the ground.
I Just finished building a 256 processor Simulation System...
Just a thought