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Old 02-25-2009, 04:47 PM   #161
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that looks slightly fabricated to say the least!
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Old 02-25-2009, 05:18 PM   #162
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Originally Posted by patsmx5 View Post
Here's a chart I found that relates pressure to speed. Funny it doesn't mention frontal area... You know, since more area = more pressure....
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
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Old 02-25-2009, 05:28 PM   #163
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patsmx5 is pissed, lol.
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Old 02-25-2009, 05:33 PM   #164
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Quote:
Originally Posted by ThePass View Post
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
What? How can you increase the pressure... without increasing the pressure? Your argument makes no sense. The idea is to increase the delta P across the heat exchangers.

Savington said:

Quote:
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.
If you increase the pressure, you increase the pressure. I'm just not buying that adding more area to the front causes compression. You're not gonna compress it significantly with any type of shroud/ changing area of the opening.
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Old 02-25-2009, 05:35 PM   #165
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patsmx5 is pissed, lol.
I am? I want to know more about these bumpers that compress air. Might can build a fancy one that supplies boost to my engine and ditch this turbo ****. Sounds like we're on to something!
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Old 02-25-2009, 05:35 PM   #166
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pat, I believe you have been bested...
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Old 02-25-2009, 08:52 PM   #167
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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.
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Old 02-25-2009, 09:59 PM   #168
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Quote:
Originally Posted by crashnscar View Post
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.
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.
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Old 02-25-2009, 10:13 PM   #169
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Quote:
Originally Posted by patsmx5 View Post
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.
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).
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Old 02-25-2009, 10:21 PM   #170
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Quote:
Originally Posted by crashnscar View Post
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.
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.
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Old 02-25-2009, 10:34 PM   #171
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Quote:
Originally Posted by deliverator View Post
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).
Consider the following. Say we stand the car up on its end, bumper pointing straight up. We hook a gauge up to measure pressure right at the surface of the radiator (red x). We first install the stock shrouding and fill the front end up with water till it's at the top of the bumper and measure the pressure at the radiator. Then we add this custom bumper we built that has a huge opening to feed the radiator, much more area, etc. The opening at the bumper is very large in comparison to the radiator. Which will have a higher pressure at the radiator?

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Old 02-25-2009, 11:06 PM   #172
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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
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Old 02-25-2009, 11:40 PM   #173
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Quote:
Originally Posted by mazda/nissan View Post
yeah but pat, why would we want an opening bigger than our radiator?
That's a good question. Sav and others believe a bigger opening will compress the air, creating a larger delta P.

Quote:
Originally Posted by mazda/nissan View Post
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.
You'll note that the opening in the front has some area. And while the radiator also has some area which appears larger dimensionally, the radiator is not 100% open like the mouth is. It has tubes and fins because water has to pass through it. So really the area of the radiator for which air actually passes through is not as big as you think. Maybe 50% of the radiator is actually "open" to let air flow. Call this the effective area. Kinda closer to the area of the mouth, no?


Quote:
Originally Posted by mazda/nissan View Post
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.
So which area matters, the dimensional area or the effective area? Is there any benefit of trying to move more air in than you can move out?

Quote:
Originally Posted by mazda/nissan View Post
The most efficiently designed mouth would be EXACTLY the same size as the radiator
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.
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Old 02-26-2009, 12:35 AM   #174
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Quote:
Originally Posted by patsmx5 View Post
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.
I know you aren't saying to cover it up, but I am using that to illustrate my point. By your theory, if opening up the front bumper doesn't increase pressure the radiator sees, and pressure is what is important for cooling, then closing up the front bumper wouldn't decrease pressure the radiator sees.
Yes, I know a radiators surface isn't completely open for air to pass through, but have no idea what the correct percentage is.

Quote:
Originally Posted by deliverator View Post
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).
Agreed... it's not necessarily that more psi is building up, but that more air is moving through the radiator by letting that same pressure act on a larger surface.

Quote:
Originally Posted by sixshooter View Post
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.
This is the one theory that I mentioned I had thought about before. Do you have any knowledge/facts to back up the theory other than old school race cars using them?

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???
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Old 02-26-2009, 12:39 AM   #175
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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.
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Old 02-26-2009, 01:01 AM   #176
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Originally Posted by TrickerZ View Post
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.
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.
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Old 02-26-2009, 03:20 AM   #177
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Originally Posted by patsmx5 View Post
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.
I'm not sure about everyone else, but I'm not talking about compressing air. I'm talking about taking the same air, but actually give it the entire surface area to take its same pressure over (or at least the "effective area" as you defined it).
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Old 02-26-2009, 10:48 AM   #178
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I believe that this article should answer some questions about proper ducting.
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Old 02-26-2009, 11:18 AM   #179
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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.
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Old 02-26-2009, 04:23 PM   #180
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Quote:
Originally Posted by mazda/nissan View Post
I believe that this article should answer some questions about proper ducting.
Quotes from your article.

Quote:
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.
Hmm.....


Quote:
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.
Ahh......



Quote:
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.
Ohh......



Quote:

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.
Ahh.....
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