josh green
06-26-2006, 11:28 AM
YOU THINK YOU KNOW ABOUT COOLING SYSTEMS, well this guy does. Sorry the pictures were no longer up for some of his explanations. This is also a good example as to why the "JDM hood prop" is worthless and can only make your car run warmer NOT cooler.
While I do not have a lot of direct experience with this I have researched cooling a ton (I love this kind of stuff) and will soon get my feet very wet with this very topic. Let me first say that running 2 minutes at WOT is a serious challenge on a number of levels. Even on the longest road racing circuits the most you will see is 70% WOT per lap. The closest thing you will find to this length of sustained WOT will be in NASCAR, the salt flats and in Silver State type open road racing. With that said, the fundamentals of cooling apply to all forms of racing so let’s jump in.
Obviously radiator and oil cooling capacity are essential (as are diff. and trany cooling but we will leave that out of this discussion) and can be quantified with a somewhat linear relationship to power output. What is more difficult quantify and is of even greater importance to the cooling equation is airflow across the coolers.
The essential consideration in airflow (that is 99.99% of time ignored) is sealing of radiator, oil cooler and intercooler to the airflow. Simply put, air would rather go around a radiator than through it. Lack of ducting and sealing from the leading edge openings to the radiator is the single biggest mistake made in cooling systems.
The next biggest mistake is the underutilization of the low pressure area over the hood. More specifically the front half of the hood. The airflow capacity available out the hood is way more that from out the bottom of the car! Automakers are obviously aware of this but seem reluctant (except on the 03-04 Cobras) to tap it.
I love to reference this air pressure schematic. Yes, I know it isn't a Mustang but a Mustang's pressure zones will be very similar.
The yellow sections with outward pointing arrows represent low pressure and the white areas high pressure. A couple points,
1) You can see why NASCAR teams pull air from the HIGH pressure area at the back of the hood into their carbs.
2) You can also see why you don't want this to be vented to anything but an air intake. If this pressure enters the engine compartment it will reduce the pressure behind the radiator and thus reduce flow.
3) You want as low a pressure area as possible BEHIND the radiator and as High a pressure as possible in front. To accomplish this you MUST duct and seal the front openings of the car to the front of the radiator/oil cooler/intercooler. You must also seal of the high pressure at the rear of the hood. And last, to maximize efficiency you must vent to hood behind the radiator.
Just like my three year old daughter, I like pictures. I have learned more from looking at elite race cars than I ever would in school. I have literally THOUSANDS (>10 GB) of pictures of professionally engineered race cars. While the drag racer guys do some things very well you must look to the highest levels of road racing for the solutions to these problems.
So lets take a look:
Ahhhhh. This car is pure sex to me. The Prodrive group in England built and races this car for Aston-Martin in ALMS GT1. This, in my opinion, is the pinnacle of 'Production Based' race cars. The reason I have shown it here is that can and does make 650 horsepower for 24 hours in 100 deg. heat. The other reason is that it's hood represents exactly what I am talking about with venting. Notice that the leading edge of the vents have a raised lip to venturi the laminar airflow which creates even greater negative pressure behind the radiator. Nice! The last thing I want you to see is that the main upper opening in the nose isn't. That is right, the center of that opening is covered with a carbon fiber panel. Why? Two reasons, 1) Downforce 2) Reduced cooling efficiency - See RX7 above.
I want to apologize in advance for putting a Chevy on this forum. Take comfort in knowing that it is as much a Chevy as Jeff Gordon's NASCAR.
Ahhhhhh again. This, BTW, is the Pratt & Miller C6R Corvette. Let this be Exhibit A in how to vent AND DUCT a hood to a radiator. (Yes, I know, it has no fan. More on that later.) Of note here is that 100% of the air entering the radiator comes out of the hood. Smart? Indeed. Also take a look at how much air enters at the back of the hood - None! Again 650 horsepower, 100 deg., 24 hours. Just as an FYI, the hood I am building for my car is a 100% direct copy of this, just on a Mustang and just 5 lbs. at that.
This is a shot of a Japanese Touring Car Supra to show that this can work with turbo cars as well.
BTW, If you want more pictures of this kind of stuff let me know. I have hundreds on just this topic.
Now a word on radiators. I hit this second to airflow because in my opinion airflow is more important and much more often screwed up. Conventional wisdom would say thicker is better but this isn't necessarily the case. The thicker the radiator the greater the air pressure drop and therefore the lower the airflow across the core. The increased capacity and surface area can often make up for this however. My philosophy is that just like an intercooler, you are better off with a tall and wide radiator than a thick one, especially at low speed. Obviously there are constraints with height and width so thickness often must be increased. Where a thick radiator becomes a problem is in stop and go traffic. With a fan supplying all of the airflow, a four inch thick radiator will often not cool as well as a two inch thick one.
With respect to fans, you will notice that the cars pictures above don't have them. Why Not? Because they hinder airflow at speed and these cars spend very little time sitting still. I have read that on a Mustang anything over 45 mph you are better off with the fan OFF than on as the spinning blades restrict flow. This is with a largely unsealed (to airflow) radiator. I would guess that this speed is much lower with a completely sealed and ducted radiator. I won't go into fan size, style and shroud here as that would be a whole other thread but keep in mind that sealing the fan shroud to the radiator is essential to creating flow across the core.
While I do not have a lot of direct experience with this I have researched cooling a ton (I love this kind of stuff) and will soon get my feet very wet with this very topic. Let me first say that running 2 minutes at WOT is a serious challenge on a number of levels. Even on the longest road racing circuits the most you will see is 70% WOT per lap. The closest thing you will find to this length of sustained WOT will be in NASCAR, the salt flats and in Silver State type open road racing. With that said, the fundamentals of cooling apply to all forms of racing so let’s jump in.
Obviously radiator and oil cooling capacity are essential (as are diff. and trany cooling but we will leave that out of this discussion) and can be quantified with a somewhat linear relationship to power output. What is more difficult quantify and is of even greater importance to the cooling equation is airflow across the coolers.
The essential consideration in airflow (that is 99.99% of time ignored) is sealing of radiator, oil cooler and intercooler to the airflow. Simply put, air would rather go around a radiator than through it. Lack of ducting and sealing from the leading edge openings to the radiator is the single biggest mistake made in cooling systems.
The next biggest mistake is the underutilization of the low pressure area over the hood. More specifically the front half of the hood. The airflow capacity available out the hood is way more that from out the bottom of the car! Automakers are obviously aware of this but seem reluctant (except on the 03-04 Cobras) to tap it.
I love to reference this air pressure schematic. Yes, I know it isn't a Mustang but a Mustang's pressure zones will be very similar.
The yellow sections with outward pointing arrows represent low pressure and the white areas high pressure. A couple points,
1) You can see why NASCAR teams pull air from the HIGH pressure area at the back of the hood into their carbs.
2) You can also see why you don't want this to be vented to anything but an air intake. If this pressure enters the engine compartment it will reduce the pressure behind the radiator and thus reduce flow.
3) You want as low a pressure area as possible BEHIND the radiator and as High a pressure as possible in front. To accomplish this you MUST duct and seal the front openings of the car to the front of the radiator/oil cooler/intercooler. You must also seal of the high pressure at the rear of the hood. And last, to maximize efficiency you must vent to hood behind the radiator.
Just like my three year old daughter, I like pictures. I have learned more from looking at elite race cars than I ever would in school. I have literally THOUSANDS (>10 GB) of pictures of professionally engineered race cars. While the drag racer guys do some things very well you must look to the highest levels of road racing for the solutions to these problems.
So lets take a look:
Ahhhhh. This car is pure sex to me. The Prodrive group in England built and races this car for Aston-Martin in ALMS GT1. This, in my opinion, is the pinnacle of 'Production Based' race cars. The reason I have shown it here is that can and does make 650 horsepower for 24 hours in 100 deg. heat. The other reason is that it's hood represents exactly what I am talking about with venting. Notice that the leading edge of the vents have a raised lip to venturi the laminar airflow which creates even greater negative pressure behind the radiator. Nice! The last thing I want you to see is that the main upper opening in the nose isn't. That is right, the center of that opening is covered with a carbon fiber panel. Why? Two reasons, 1) Downforce 2) Reduced cooling efficiency - See RX7 above.
I want to apologize in advance for putting a Chevy on this forum. Take comfort in knowing that it is as much a Chevy as Jeff Gordon's NASCAR.
Ahhhhhh again. This, BTW, is the Pratt & Miller C6R Corvette. Let this be Exhibit A in how to vent AND DUCT a hood to a radiator. (Yes, I know, it has no fan. More on that later.) Of note here is that 100% of the air entering the radiator comes out of the hood. Smart? Indeed. Also take a look at how much air enters at the back of the hood - None! Again 650 horsepower, 100 deg., 24 hours. Just as an FYI, the hood I am building for my car is a 100% direct copy of this, just on a Mustang and just 5 lbs. at that.
This is a shot of a Japanese Touring Car Supra to show that this can work with turbo cars as well.
BTW, If you want more pictures of this kind of stuff let me know. I have hundreds on just this topic.
Now a word on radiators. I hit this second to airflow because in my opinion airflow is more important and much more often screwed up. Conventional wisdom would say thicker is better but this isn't necessarily the case. The thicker the radiator the greater the air pressure drop and therefore the lower the airflow across the core. The increased capacity and surface area can often make up for this however. My philosophy is that just like an intercooler, you are better off with a tall and wide radiator than a thick one, especially at low speed. Obviously there are constraints with height and width so thickness often must be increased. Where a thick radiator becomes a problem is in stop and go traffic. With a fan supplying all of the airflow, a four inch thick radiator will often not cool as well as a two inch thick one.
With respect to fans, you will notice that the cars pictures above don't have them. Why Not? Because they hinder airflow at speed and these cars spend very little time sitting still. I have read that on a Mustang anything over 45 mph you are better off with the fan OFF than on as the spinning blades restrict flow. This is with a largely unsealed (to airflow) radiator. I would guess that this speed is much lower with a completely sealed and ducted radiator. I won't go into fan size, style and shroud here as that would be a whole other thread but keep in mind that sealing the fan shroud to the radiator is essential to creating flow across the core.