240_to_miata

iTrader: (2)

that looks slightly fabricated to say the least!

ThePass

iTrader: (3)

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

hustler

iTrader: (6)

patsmx5 is pissed, lol.

patsmx5

iTrader: (16)

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:

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.

patsmx5

iTrader: (16)

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!

mazda/nissan

iTrader: (2)

pat, I believe you have been bested...

crashnscar

iTrader: (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.

patsmx5

iTrader: (16)

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.

deliverator

iTrader: (14)

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).

sixshooter

iTrader: (12)

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.

patsmx5

iTrader: (16)

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?

mazda/nissan

iTrader: (2)

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

patsmx5

iTrader: (16)

That's a good question. Sav and others believe a bigger opening will compress the air, creating a larger delta P.

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?


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?

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.

crashnscar

iTrader: (9)

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.

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.

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???

TrickerZ

iTrader: (6)

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.

patsmx5

iTrader: (16)

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.

crashnscar

iTrader: (9)

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).

mazda/nissan

iTrader: (2)

I believe that this article should answer some questions about proper ducting.

leatherface24

iTrader: (10)

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.

patsmx5

iTrader: (16)

Quotes from your article.

Hmm.....


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