intercooling size ? for Mike P
Posted: Sat Nov 10, 2001 4:47 am
In a message dated 11/09/01 12:28:46 AM Pacific Standard Time, Mike P writes:
Subject: intercooling size?
i need some input on an intercooler size and the flow of it. the
size would be approx. 35"x5"x3" and would be front mounted and
air/air. would that get me any cooler air? or would it do more harm
than good?
Hey Mike,
You've already had some good feedback, but maybe I can add a couple of nickels. Intercooling is one of my fave subjects. So if you don't mind, I'd like to answer your question by starting out with a question for you. What do you want to do? You might lean towards one style cooler or another depending. There's advantages and disadvantages to both, and it seems like you're still kind of searching for that happy medium. Seems like you're dialed into a front mounted air-to-air, and that's cool, they have their place in line too. By what do you want to do, what I mean is, what will be the primary job for your chiller? Are you going to be boosting for extended periods of time, like the Paris to Dakar Rally? Do you want to be at the top of the food chain at Pikes Peak? Extended boost periods at high speed like air-! to-air intercoolers. There is an almost infinite amount of air in the air, so that no matter how fast and furious you go, there will always be enough, and the faster you go, the better the flow thru a front mount will work for you. That is, assuming whoever puts your system together knows what the heck they were doing and gets the sizing correct, and the plumbing in right, so your pressure drop is acceptable.
There is a catch 22 with intercooling. Generally, the bigger the better and the biggest fit best in front. But in front is where you have to have the most plumbing back to the turbo. The catch is the bigger your cooler and the more plumbing your turbo has to pump through, the greater will be the pressure drop. So you have to increase the boost to offset the pressure drop, and that heats the air to offset the advantages of the intercooler. It is a balancing act, but it is easier to balance if you are intending to run big boost thru a big turbo, which will flow lots of air without heating so much over an extended period. This is what the serious guys do. But they have engines which support big horsepower and don't always care about what the car would drive like on the street, if they ever put it on the street. They need the most efficient charge air cooling available, and the big front mount air-to-air is just that for those extend! ed operation type of applications. And it is why most people will argue that air-to-air is more efficient than air-to-water. And they are partially correct. However, if you don't have a bigtime engine, you might find yourself tiring of those Yugos that jump away from you at the green unless you dump the clutch at five and a half to get above your turbo lag rpm.
But what you say? Partially correct? Let's go back. An air-to-water, unlike an air-to-air, is a closed system. There is not an almost infinite amount of water available for cooling, unless your car is also a boat, which all use air-to-water. In an automotive air-to-water intercooler system, there is only so much extended boost you can operate before the water starts to heat up just like engine coolant does, and the efficiency is lost or even reversed, so that what you then have is what intercooler freaks call an interheater. There are also those who will argue that since the water is cooled by air, it can never be cooler than the air, and so can never be as efficient as an air-to-air cooler. And again, they are partially correct. The reason I say partially correct is because there are other modes of operation where air-to-water beats air-to-air.
That theoretical efficiency business is fine for a steady state run up Pike's Peak, but under intermittent short duration boost conditions, like at a dragstrip, or in my case, away from a stoplight or up a freeway onramp for a few seconds, air-to-water exhibits greater effective efficiency. Who do I think I am to claim that? OK hang with me. In a short duration boost event, the heat sink that is your intercooler, doesn't have a chance to stabilize at the steady state heat transfer condition that an extended run allows. A boost which is only a half a minute or quarter of a minute long depends on the temperature inertia of the intercooler heat sink to cool the air charge. An air-to-air heat exchanger will be heated to that steady state temperature much more quickly than one which has a volume of water soaking up the heat without changing temperature much. Prove it to yourself with the tongue test. Take one car with an A/A and another wit! h an A/W and right after they finish a quarter mile blast, run over and hold your tongue against each intercooler. Don't pay any attention to spectators comments. The deal is, with driving on the street, and other events with typically short boost duration, it's all over before that steady state efficiency ever comes into play. During that transition from rest, to boost induced temperature rise, and back to rest, the air-to-water hardly moves on the temp scale while the air-to-air can experience a rapid rise in temperature. The air-to-water is more effective at cooling during these short events...its' effective efficiency is greater.
Air-to-air has fewer components, just the heat exchanger and the plumbing. Air-to-water needs, besides the heat exchanger and plumbing, a separate radiator to cool the water, and a pump and plumbing to circulate the water from the radiator to the heat exchanger. Usually there is a separate additional water reservoir to increase the water volume and inertia of the system. The upside is because of the superior heat absorption characteristics of the water, a smaller heat exchanger may be used, which may allow placement closer to the turbo, thus minimizing plumbing and pressure loss.
Another question we need to explore is how much boost you plan to run? For "normal" Subaru levels of boost, there are Subaru air-to-air intercoolers designed to mount right in back of the intake manifold, in front of the firewall real close to the turbo. They work surprisingly well for normal Subaru boost levels, considering they sit over the engine. Standard on all WRX and overseas Turbo Legacy. The hood scoop ducts cooling air right thru the heat exchanger. The earlier overseas Turbo Legacy like ours used air-to-water, which is my preference for street use as explained above. If you're dead set on the front mount, those are available too, and sounds like you've even got one picked out. If you plan to maintain your stock boost it would do more harm than good since our pitiful 8.7 pounds doesn't even need an intercooler, which was a cost savings for the factory.
The 35" x 5" x 3" size you have chosen might require some bodywork modification. I suggest you cut a piece of cardboard to 5" x 3" and try to slide it along the 35" length you plan on. If you don't plan to cut any of your front end away, I think you'll find a 4" x 2" piece is about as big as the space can handle.
That's about it from me, hope I was able to give you some stuff you didn't already know. If not check out these intercooler specific links below.
Here's links from my intercooler file
http://www.autospeed.com/A_0090/page1.html complete A/W cooling guide
http://www.autospeed.com/A_0754/page1.html intercooler airflow page 1 only
http://www.autospeed.com/A_0868/P_2/article.html WRX coolers
http://www.netcomuk.co.uk/~gavinp/airwater.htm
Larry too cool to drool Witherspoon
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BC-BFLegacyWorks-unsubscribe@egroups.com
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Subject: intercooling size?
i need some input on an intercooler size and the flow of it. the
size would be approx. 35"x5"x3" and would be front mounted and
air/air. would that get me any cooler air? or would it do more harm
than good?
Hey Mike,
You've already had some good feedback, but maybe I can add a couple of nickels. Intercooling is one of my fave subjects. So if you don't mind, I'd like to answer your question by starting out with a question for you. What do you want to do? You might lean towards one style cooler or another depending. There's advantages and disadvantages to both, and it seems like you're still kind of searching for that happy medium. Seems like you're dialed into a front mounted air-to-air, and that's cool, they have their place in line too. By what do you want to do, what I mean is, what will be the primary job for your chiller? Are you going to be boosting for extended periods of time, like the Paris to Dakar Rally? Do you want to be at the top of the food chain at Pikes Peak? Extended boost periods at high speed like air-! to-air intercoolers. There is an almost infinite amount of air in the air, so that no matter how fast and furious you go, there will always be enough, and the faster you go, the better the flow thru a front mount will work for you. That is, assuming whoever puts your system together knows what the heck they were doing and gets the sizing correct, and the plumbing in right, so your pressure drop is acceptable.
There is a catch 22 with intercooling. Generally, the bigger the better and the biggest fit best in front. But in front is where you have to have the most plumbing back to the turbo. The catch is the bigger your cooler and the more plumbing your turbo has to pump through, the greater will be the pressure drop. So you have to increase the boost to offset the pressure drop, and that heats the air to offset the advantages of the intercooler. It is a balancing act, but it is easier to balance if you are intending to run big boost thru a big turbo, which will flow lots of air without heating so much over an extended period. This is what the serious guys do. But they have engines which support big horsepower and don't always care about what the car would drive like on the street, if they ever put it on the street. They need the most efficient charge air cooling available, and the big front mount air-to-air is just that for those extend! ed operation type of applications. And it is why most people will argue that air-to-air is more efficient than air-to-water. And they are partially correct. However, if you don't have a bigtime engine, you might find yourself tiring of those Yugos that jump away from you at the green unless you dump the clutch at five and a half to get above your turbo lag rpm.
But what you say? Partially correct? Let's go back. An air-to-water, unlike an air-to-air, is a closed system. There is not an almost infinite amount of water available for cooling, unless your car is also a boat, which all use air-to-water. In an automotive air-to-water intercooler system, there is only so much extended boost you can operate before the water starts to heat up just like engine coolant does, and the efficiency is lost or even reversed, so that what you then have is what intercooler freaks call an interheater. There are also those who will argue that since the water is cooled by air, it can never be cooler than the air, and so can never be as efficient as an air-to-air cooler. And again, they are partially correct. The reason I say partially correct is because there are other modes of operation where air-to-water beats air-to-air.
That theoretical efficiency business is fine for a steady state run up Pike's Peak, but under intermittent short duration boost conditions, like at a dragstrip, or in my case, away from a stoplight or up a freeway onramp for a few seconds, air-to-water exhibits greater effective efficiency. Who do I think I am to claim that? OK hang with me. In a short duration boost event, the heat sink that is your intercooler, doesn't have a chance to stabilize at the steady state heat transfer condition that an extended run allows. A boost which is only a half a minute or quarter of a minute long depends on the temperature inertia of the intercooler heat sink to cool the air charge. An air-to-air heat exchanger will be heated to that steady state temperature much more quickly than one which has a volume of water soaking up the heat without changing temperature much. Prove it to yourself with the tongue test. Take one car with an A/A and another wit! h an A/W and right after they finish a quarter mile blast, run over and hold your tongue against each intercooler. Don't pay any attention to spectators comments. The deal is, with driving on the street, and other events with typically short boost duration, it's all over before that steady state efficiency ever comes into play. During that transition from rest, to boost induced temperature rise, and back to rest, the air-to-water hardly moves on the temp scale while the air-to-air can experience a rapid rise in temperature. The air-to-water is more effective at cooling during these short events...its' effective efficiency is greater.
Air-to-air has fewer components, just the heat exchanger and the plumbing. Air-to-water needs, besides the heat exchanger and plumbing, a separate radiator to cool the water, and a pump and plumbing to circulate the water from the radiator to the heat exchanger. Usually there is a separate additional water reservoir to increase the water volume and inertia of the system. The upside is because of the superior heat absorption characteristics of the water, a smaller heat exchanger may be used, which may allow placement closer to the turbo, thus minimizing plumbing and pressure loss.
Another question we need to explore is how much boost you plan to run? For "normal" Subaru levels of boost, there are Subaru air-to-air intercoolers designed to mount right in back of the intake manifold, in front of the firewall real close to the turbo. They work surprisingly well for normal Subaru boost levels, considering they sit over the engine. Standard on all WRX and overseas Turbo Legacy. The hood scoop ducts cooling air right thru the heat exchanger. The earlier overseas Turbo Legacy like ours used air-to-water, which is my preference for street use as explained above. If you're dead set on the front mount, those are available too, and sounds like you've even got one picked out. If you plan to maintain your stock boost it would do more harm than good since our pitiful 8.7 pounds doesn't even need an intercooler, which was a cost savings for the factory.
The 35" x 5" x 3" size you have chosen might require some bodywork modification. I suggest you cut a piece of cardboard to 5" x 3" and try to slide it along the 35" length you plan on. If you don't plan to cut any of your front end away, I think you'll find a 4" x 2" piece is about as big as the space can handle.
That's about it from me, hope I was able to give you some stuff you didn't already know. If not check out these intercooler specific links below.
Here's links from my intercooler file
http://www.autospeed.com/A_0090/page1.html complete A/W cooling guide
http://www.autospeed.com/A_0754/page1.html intercooler airflow page 1 only
http://www.autospeed.com/A_0868/P_2/article.html WRX coolers
http://www.netcomuk.co.uk/~gavinp/airwater.htm
Larry too cool to drool Witherspoon
To unsubscribe from this group, please send an email to:
BC-BFLegacyWorks-unsubscribe@egroups.com
zZz <http://docs.yahoo.com/info/terms/> .