Your thoughts on the enormous new hole in my bumper.
#162
Supporting Vendor
iTrader: (3)
Join Date: Jul 2006
Location: San Diego
Posts: 3,303
Total Cats: 1,216
-Ryan
#164
Sure it does. PSI - pounds per square inch. So each square inch gets a given amount of pressure at a given air speed. Savington said increasing the frontal area increases the pressure on the radiator, not that it increases the pressure per square inch, basically only that a radiator with a stock sized bumper opening does not get airflow to the entire frontal surface of it. Increasing the opening size increases the net pressure on the radiator i.e. more square inches at the same psi = more net pressure.
-Ryan
-Ryan
Savington said:
Increase the frontal area and you increase the pressure against the radiator. Ducting does the same thing, just more effectively (and with more effort). Pressure deltas are the name of the game.
#167
Former Vendor
iTrader: (9)
Join Date: Jan 2008
Location: Bay Area, California
Posts: 929
Total Cats: 9
patsmx5, why don't we all cover up the oem opening on our bumpers except for a 1/4" slit? According to your theory, it will still see the same pressure right? Shouldn't change our cooling at all?
And your drawings aren't like a miata's cooling setup at all. The two green lines would need to come to about half the size of the radiator (no, I haven't done any measurements, but just from looking). If the entire radiator was exposed no matter what (at least picture b), it may be a different story.
And your drawings aren't like a miata's cooling setup at all. The two green lines would need to come to about half the size of the radiator (no, I haven't done any measurements, but just from looking). If the entire radiator was exposed no matter what (at least picture b), it may be a different story.
#168
patsmx5, why don't we all cover up the oem opening on our bumpers except for a 1/4" slit? According to your theory, it will still see the same pressure right? Shouldn't change our cooling at all?
And your drawings aren't like a miata's cooling setup at all. The two green lines would need to come to about half the size of the radiator (no, I haven't done any measurements, but just from looking). If the entire radiator was exposed no matter what (at least picture b), it may be a different story.
And your drawings aren't like a miata's cooling setup at all. The two green lines would need to come to about half the size of the radiator (no, I haven't done any measurements, but just from looking). If the entire radiator was exposed no matter what (at least picture b), it may be a different story.
Sav and others seem to think that adding a bigger opening will cause pressure to build up in front of the radiator. (bumper and shrouds compressing air). I don't buy that. Largely because the air doesn't have enough mass or velocity at the speeds we drive at to to compress significantly. Again, I'm not saying cover up your opening. I'm saying a bigger opening doesn't increase the pressure the front of the radiator sees. Several here seem to think that is the case however.
You do realize that only a certain percentage of the radiators surface is actually open to allow air to pass through, right? What, maybe 50% or so? I bet the area of the opening in the mouth is about equal to the area of the radiator that's actually open where air flows across it.
#169
Sav and others seem to think that adding a bigger opening will cause pressure to build up in front of the radiator. (bumper and shrouds compressing air). I don't buy that. Largely because the air doesn't have enough mass or velocity at the speeds we drive at to to compress significantly. Again, I'm not saying cover up your opening. I'm saying a bigger opening doesn't increase the pressure the front of the radiator sees. Several here seem to think that is the case however.
What's going to flow more air? Arbitrarily picking 2 PSI of air pressure
2 pounds per square inch of air against/through 48 square inches?
or
2 pounds per square inch of air against/through 100 square inches?
Seems to me like larger openings mean more air through the heat exchangers (assuming that all air through the opening(s) passes through the heat exchangers, anyway).
#170
Moderator
iTrader: (12)
Join Date: Nov 2008
Location: Tampa, Florida
Posts: 20,681
Total Cats: 3,019
Why is no thermostat failing? The thermostat is there to keep the car operating at a certain temperature on the street, where without one it would run too cold, especially on a cold winter night. BTW, this isn't on a Miata motor, but I'd still like an explanation of why no thermostat is so bad. I actually have one reason that I know of that it could be bad, but am not completely convinced it is true.
If they were to overheat anyway then they obviously didn't have a large enough or efficient enough radiator for the amount of HP (heat) they were creating. But with them if the problem was that they didn't have enough airflow to the radiator, they just cut the hole bigger!
If it is a race car then it isn't supposed to be pretty first and functional second. Pretty first and functional second means loser at the track everytime.
#171
Ok. Pressures is what? Force per unit of area.
What's going to flow more air? Arbitrarily picking 2 PSI of air pressure
2 pounds per square inch of air against/through 48 square inches?
or
2 pounds per square inch of air against/through 100 square inches?
Seems to me like larger openings mean more air through the heat exchangers (assuming that all air through the opening(s) passes through the heat exchangers, anyway).
What's going to flow more air? Arbitrarily picking 2 PSI of air pressure
2 pounds per square inch of air against/through 48 square inches?
or
2 pounds per square inch of air against/through 100 square inches?
Seems to me like larger openings mean more air through the heat exchangers (assuming that all air through the opening(s) passes through the heat exchangers, anyway).
#172
yeah but pat, why would we want an opening bigger than our radiator? The stock mouth is smaller than the radiator, so people chop up holes to make the mouth larger, but still it is smaller than the radiator. If we kept opening up the mouth past the size of the radiator, and had the ducting so the air would go nowhere else, then that would be larger than needed. The most efficiently designed mouth would be EXACTLY the same size as the radiator
#173
Same size or same area? Which area? If you had an opening that was "EXACTLY" the same physical size as the dimensions of the radiator, it would have a much larger area than the effective area of the radiator.
#174
Former Vendor
iTrader: (9)
Join Date: Jan 2008
Location: Bay Area, California
Posts: 929
Total Cats: 9
The drawings are indeed not to scale and are intentionally exaggerated to illustrate my point. I wouldn't cover up the OEM opening. I have never made such claims.
Sav and others seem to think that adding a bigger opening will cause pressure to build up in front of the radiator. (bumper and shrouds compressing air). I don't buy that. Largely because the air doesn't have enough mass or velocity at the speeds we drive at to to compress significantly. Again, I'm not saying cover up your opening. I'm saying a bigger opening doesn't increase the pressure the front of the radiator sees. Several here seem to think that is the case however.
You do realize that only a certain percentage of the radiators surface is actually open to allow air to pass through, right? What, maybe 50% or so? I bet the area of the opening in the mouth is about equal to the area of the radiator that's actually open where air flows across it.
Sav and others seem to think that adding a bigger opening will cause pressure to build up in front of the radiator. (bumper and shrouds compressing air). I don't buy that. Largely because the air doesn't have enough mass or velocity at the speeds we drive at to to compress significantly. Again, I'm not saying cover up your opening. I'm saying a bigger opening doesn't increase the pressure the front of the radiator sees. Several here seem to think that is the case however.
You do realize that only a certain percentage of the radiators surface is actually open to allow air to pass through, right? What, maybe 50% or so? I bet the area of the opening in the mouth is about equal to the area of the radiator that's actually open where air flows across it.
Yes, I know a radiators surface isn't completely open for air to pass through, but have no idea what the correct percentage is.
Ok. Pressures is what? Force per unit of area.
What's going to flow more air? Arbitrarily picking 2 PSI of air pressure
2 pounds per square inch of air against/through 48 square inches?
or
2 pounds per square inch of air against/through 100 square inches?
Seems to me like larger openings mean more air through the heat exchangers (assuming that all air through the opening(s) passes through the heat exchangers, anyway).
What's going to flow more air? Arbitrarily picking 2 PSI of air pressure
2 pounds per square inch of air against/through 48 square inches?
or
2 pounds per square inch of air against/through 100 square inches?
Seems to me like larger openings mean more air through the heat exchangers (assuming that all air through the opening(s) passes through the heat exchangers, anyway).
Been down that road years ago and the answer is to regulate the speed of the coolant flow through the radiator. If the coolant passes too quickly through the radiator then it doesn't cool enough before returning to the engine. In race cars (old school roundy round type), they would use a certain size restrictor in place of the thermostat if they decided not to run one. If they did not use either a thermostat or restrictor, then the engine would overheat.
If they were to overheat anyway then they obviously didn't have a large enough or efficient enough radiator for the amount of HP (heat) they were creating. But with them if the problem was that they didn't have enough airflow to the radiator, they just cut the hole bigger!
If it is a race car then it isn't supposed to be pretty first and functional second. Pretty first and functional second means loser at the track everytime.
If they were to overheat anyway then they obviously didn't have a large enough or efficient enough radiator for the amount of HP (heat) they were creating. But with them if the problem was that they didn't have enough airflow to the radiator, they just cut the hole bigger!
If it is a race car then it isn't supposed to be pretty first and functional second. Pretty first and functional second means loser at the track everytime.
The other way of looking at it is: the radiator doesn't care, or know, how fast the water is moving. It only cares what temperature the water is. The faster the water moves through, the less heat it will pick up per volume of water, but a larger volume of water is moving through.
Thinking about it though, there is probably an optimal flow rate where faster doesn't give enough time for the water to "absorb" the heat and then dissipate it in the radiator, and slower is not flowing enough volume to cool it fast enough.
How can you determine what size restrictor to use? I'm up for trying just about anything (within reason and that makes sense) to get this motor to not overheat.
And what is the pretty/functional comment about???
#175
Has anyone done any modeling? Does anyone at least have aerodynamics classes under their belt? Just curious if any of the opinions are relevant...
I haven't taken any aerodynamics classes, but my understanding from friends who have is that higher pressures can cause less air to go through from some turbulence thing. Maximizing surface area and reducing restriction on flow is what helps. And if you can make it so the flow of air over the car actually causes a suction, that increases the flow a lot. The ducting will help to force air where you want it and not lose flow.
I would think it should all be similar to the thought process behind exhaust manifolds and piping for a turbo. Direct more air into the turbine with less restriction so the turbine is the restrictive part, and make sure the back side is nice and open to reduce the back pressure. And you really don't want leaks before hitting the turbine.
If someone has access to modeling software, I'd certainly be interested in seeing the effects. I'm sure the Miata from stock configuration would benefit from extraction more than intake. If anyone has a spare MAP sensor, they should put it under the hood and see what the reading is at 60mph or so. I wonder what it'd take to get it under 100kpa.
I haven't taken any aerodynamics classes, but my understanding from friends who have is that higher pressures can cause less air to go through from some turbulence thing. Maximizing surface area and reducing restriction on flow is what helps. And if you can make it so the flow of air over the car actually causes a suction, that increases the flow a lot. The ducting will help to force air where you want it and not lose flow.
I would think it should all be similar to the thought process behind exhaust manifolds and piping for a turbo. Direct more air into the turbine with less restriction so the turbine is the restrictive part, and make sure the back side is nice and open to reduce the back pressure. And you really don't want leaks before hitting the turbine.
If someone has access to modeling software, I'd certainly be interested in seeing the effects. I'm sure the Miata from stock configuration would benefit from extraction more than intake. If anyone has a spare MAP sensor, they should put it under the hood and see what the reading is at 60mph or so. I wonder what it'd take to get it under 100kpa.
#176
Has anyone done any modeling? Does anyone at least have aerodynamics classes under their belt? Just curious if any of the opinions are relevant...
I haven't taken any aerodynamics classes, but my understanding from friends who have is that higher pressures can cause less air to go through from some turbulence thing. Maximizing surface area and reducing restriction on flow is what helps. And if you can make it so the flow of air over the car actually causes a suction, that increases the flow a lot. The ducting will help to force air where you want it and not lose flow.
I would think it should all be similar to the thought process behind exhaust manifolds and piping for a turbo. Direct more air into the turbine with less restriction so the turbine is the restrictive part, and make sure the back side is nice and open to reduce the back pressure. And you really don't want leaks before hitting the turbine.
If someone has access to modeling software, I'd certainly be interested in seeing the effects. I'm sure the Miata from stock configuration would benefit from extraction more than intake. If anyone has a spare MAP sensor, they should put it under the hood and see what the reading is at 60mph or so. I wonder what it'd take to get it under 100kpa.
I haven't taken any aerodynamics classes, but my understanding from friends who have is that higher pressures can cause less air to go through from some turbulence thing. Maximizing surface area and reducing restriction on flow is what helps. And if you can make it so the flow of air over the car actually causes a suction, that increases the flow a lot. The ducting will help to force air where you want it and not lose flow.
I would think it should all be similar to the thought process behind exhaust manifolds and piping for a turbo. Direct more air into the turbine with less restriction so the turbine is the restrictive part, and make sure the back side is nice and open to reduce the back pressure. And you really don't want leaks before hitting the turbine.
If someone has access to modeling software, I'd certainly be interested in seeing the effects. I'm sure the Miata from stock configuration would benefit from extraction more than intake. If anyone has a spare MAP sensor, they should put it under the hood and see what the reading is at 60mph or so. I wonder what it'd take to get it under 100kpa.
The modeling and data I've seen suggest that funneling air doesn't make it compress. There is not enough work done to cause substantial compression.
#177
Former Vendor
iTrader: (9)
Join Date: Jan 2008
Location: Bay Area, California
Posts: 929
Total Cats: 9
You're suggesting that power out of a turbine is the difference in enthalpy across the turbine, times its efficiency? And seeing how enthalpy is U + PdV that increasing the difference in pressure across it (high flow manifold, free flowing exhaust to reduce back pressure) or increasing the volume (engine RPM, volumetric efficiency, reducing flow losses) or the internal energy (temperature of the gases dictated by thermal efficiency of the engine) is what governs the actual work produced? Nah. It's how much area you have man. More area = more flow.
The modeling and data I've seen suggest that funneling air doesn't make it compress. There is not enough work done to cause substantial compression.
The modeling and data I've seen suggest that funneling air doesn't make it compress. There is not enough work done to cause substantial compression.
#179
Very good info in this thread. All the techincal aspects aside, my cut out that i did in both of my bumpers were good for a 20-30 degree drop in water temps. the 30 degree was with the coolant reroute. Granted, I havent tried it on a turbo car yet but levnubhin and whatmiata have both done it and its yielded significant water temps drops.
#180
I believe that this article should answer some questions about proper ducting.
The problem there is that it takes pressure, not speed, to drive the airflow. Without adequate pressure, the front face of the radiator would become a stagnation zone.
To change flow velocity into pressure in a confined space, you have to slow down the flow. Bernoulli's equation states a proportional relationship between pressure, flow area and speed. Since flow rate doesn't change much, the inverse relationship between velocity and pressure means that if flow becomes slower within an enclosed area, the pressure would rise.
The easiest way to reduce velocity is with a diverging nozzle. If the airstream enters through a small opening (small cross-sectional area) and exits a larger opening, the air velocity going out would be slower than what's going in, and the pressure would be higher at the outlet than the inlet.
A diverging nozzle or duct at the inlet of the radiator cuts the speed and increases pressure in front of the radiator. The pressure ensures that air has enough potential to push all the way through the resistance in the radiators' fins and tubing. Without that pressure, the flow would stop and all subsequent air would go around the radiator duct, making it useless.