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I have a 12" e fan to go on my 83,. BAsically because I don't have the factory fan or shroud.
I'm trying to figure out if I should do a fan shroud or not. I have a sheet of aluminum big enoigh to cover the whole rad, going to put a sheet across the entire rad with a 12" hole in it for the fan. Or just mount the fan to the rad. What would provide the best cooling?
When the car is underway you have a HUGE amount of air pressure at the front of the car being forced through the radiator with no fan required. Don't obstruct the back of the radiator with a close fitting shroud that restricts airflow. Even with the factory shroud, Mazda saw fit to include an air pressure flap at the lower left corner to prevent the fan blades while freewheeling on the fan clutch from restricting hot air coming out from the back of the radiator.
Your electric fan is best positioned to push air through from the front, as it will be working with cooler, more dense air vs. trying to suck air through the restriction of the radiator. From a thermodynamic standpoint, either will work well, but the pusher fan in front design doesn't require any shroud behind the radiator where it would restrict the free flow of air, as long as the fan blades are designed to push.
It's not going to make me any friends but a vote for no shroud here. Unless it is an oem style one with swoopy contours there's probably no point other than aesthetics and is even possibly a hindrance to natural highway airflow.
No shroud works fine. Tested and proven.
Whats the CFM on that fan? Rotaries require about 2500 cfm to cool well. That why everyone grabs the taurus efans. I have a twin setup from and MR2, each is about 12 inches. Cools great.
When the car is underway you have a HUGE amount of air pressure at the front of the car being forced through the radiator with no fan required. Don't obstruct the back of the radiator with a close fitting shroud that restricts airflow. Even with the factory shroud, Mazda saw fit to include an air pressure flap at the lower left corner to prevent the fan blades while freewheeling on the fan clutch from restricting hot air coming out from the back of the radiator.
Your electric fan is best positioned to push air through from the front, as it will be working with cooler, more dense air vs. trying to suck air through the restriction of the radiator. From a thermodynamic standpoint, either will work well, but the pusher fan in front design doesn't require any shroud behind the radiator where it would restrict the free flow of air, as long as the fan blades are designed to push.
Is the fan on the back not supposed to push air forward through the radiator? rather then suck air through the rad and back into the engine bay?
All other things being equal at low speeds, any car with a proper radiator shroud will always stay cooler than one without. This is because the shroud forces the fan to draw nearly all of its air through the radiator instead of drawing it from around the fan.
At high speeds, having no shroud will likely cool better, but high speeds are generally when additional cooling is needed the least.
Is the fan on the back not supposed to push air forward through the radiator? rather then suck air through the rad and back into the engine bay?
The idea was that having a fan on the front of the rad, pushing air into the engine bay through the rad, would be more efficient at cooling than one pulling air through from the back. Like LongDuck said, this is due to the air pre-rad being cooler and therefore more dense, meaning that the same fan could move more cold air than hot air (in terms of volume if both were brought to the same temp after the fact). While I doubt it makes much of a difference in practice, it's still something to consider when designing a cooling system.
If you had a fan on the engine bay side pushing air, that would just fight the air coming in from the car's movement which would be extremely ineffective at cooling at any speed other than stopped.
Last edited by Benjamin4456; 03-07-19 at 01:08 PM.
Pusher vs puller. They both work, but a pusher is harder to implement when you start considering other components in front of the radiator such as your A/C condenser, oil cooler, intercooler, etc etc. You want to make sure air passes through everything. With a pusher on early models, you might not reach the bottom mounted oil cooler. On -SE there may not be space between the rad and oil cooler. On anything with A/C things are going to be tricky.
Distance from the radiator. If the fan is super close to the radiator it doesn't work very well. The SPAL 16" fan I used on my REPU had an optional gasket which moved it away from the fins of the radiator by about 3/4". I cannot give you specific thermodynamic numbers to say whether it worked better, but just like placing a box fan up against a wall or in a window, it was much quieter with a little bit of space behind it. I did not run a shroud of any type, just the rubber spacer and some of those long plastic rods to mount it.
Fan Speed. The reason the factory system needs a shroud covering the entire radiator and an electric fan does not is due to the RPMs required to pull the same CFM. the factory fan can spin at idle ~800 RPMs and pull the necessary air through the shroud and keep the car cool. An electric fan is capable of running at 1500-2000 RPM even at engine idle so it can pull its max CFM through whatever section of the radiator it is connected to regardless of engine RPM and achieve the same cooling effect.
Vehicle Speed. As others have mentioned, once you get up to speed, the fan should never turn on and a mechanical fan should disengage its clutch. It cannot pull more air through the radiator than what is already being pressurized and forced through by the front facade of the vehicle. This is why heavy duty trucks have large grills. If they could have just put more fans on the radiator they wouldn't have designed something like the that new Chevy pickup everyone is laughing at because of it's immensely huge grill. This is also why large fan shrouds contain flaps that open while you are driving, to release that pressure across the entire face of the radiator.
Fan control. Sure, you can just hook the fan up to an on-off switch but modern cars utilize PWM pulse-width-modulation controllers so that you don't have to listen to a high powered fan on full tilt when your engine temp bumps 1 degree over optimal. Consider that with your overall fan strategy.
Yes, it's pricey, and you'll save a lot of money going to a pick-and-pull to grab a used Ford Taurus fan. But this kit has some advantages...
1) If my measurements are correct it will bolt up to the factory flanges of the OEM radiator, or in my case the KoyoRad replacement
2) The shroud comes with a gasket and separates the fan by over 1" from the radatior. It also comes with universal brackets which should reach the OEM mounting holes.
3) The fan is capable of 2100 CFM but the shroud also has built in flaps to allow more air to pass through when moving. I doubt we need more cooling at idle unless you're running a boosted car in stop and go traffic in extreme heat conditions.
4) It comes with a controller, and all the necessary wiring to connect directly to your battery
5) It comes with a sensor that can be attached near the outlet of your radiator, no need to plumb in anything else
6) The controller has an override which will allow you to bump the fan up to 60% velocity when you need it (typically for A/C but you could use it as a failsafe if the included sensor fails)
7) Under normal operation, it will only run the fan as fast as required to maintain the desired temperature you set on the controller.
8) If wired as they recommend, the fan will be connected directly to battery and operate even after you have turned your car off helping it cool down after a hot lapping. It's no "turbo-timer" but hey, it's a nice touch that I've seen happen to new cars on hot days.
Anyway, my fan shipped out yesterday, I should have it in a few days and I'll know then how it fits. Check my build thread (link in signature) to see how it turns out.
So what I'm getting to is if I mount to front of radiator no shroud and push air towards the engine. If I put it on the engine side of rad use well spaced shroud and pull air from .Front through the rad into the engine bay. The fans reversible I could do either and I have space up front ,AC is deleted and cooler is an FC cooler mounted to front cross member.
The fan controller I'm using is the derale adjustable fan controller. And I will have the override option hooked to the factory AC switch.
I've read that pusher fans are less efficient than puller fans, although I'm not sure the exact reason why. Might be something to do a little research on. If you have the room for the puller fan with shroud I would lean that way, since all modern vehicles use that configuration.
I have this kit and it works flawlessly. I stay around 200 with the fan on high in 100 degree weather. Thats on a very undersized radiator, 19x21x3, and a LS engine.
EDIT: actually i got this one. Its cheaper, and same size fan. Im not sure what the 100 dollar difference is
Ok so there are two difference in the kits 66820 and 16817. 66820 has 11 blades and 16817 has 8. 66820 has a 20 inch wide shroud and 16817 has a 17 in wide shroud. Both are 14 inch fans, both are 2100 cfm
But now I see that the other fan has the controller integrated into the unit and comes with all of the electrical components and sensor.
Yup, I was interested in the PWM controller which was initially lead me to Derale's website. If you can bend thick sheet aluminum, I'm sure you could fab up your own, but I don't have access to a metal brake so the kit made sense.
A quick update on how the DER-66820 kit fits with the KoyoRad radiator. I posted more pics in my build thread but I'll review it here as well.
The fitment near the return neck was really tight. I got it in without modifications but I didn't like the corner touching the hose clamp, so I made some modifications...
1) I flippped it upside down, this puts the controller on the lower left close to the battery.
2) I drilled new holes for the top flaps so they would hang properly. I left the bottom flap near the filler neck as-is since it won't open downward with the return neck in the way
3) using my table saw and a metal cutting blade, I skimmed off about 3/8" from the top (which is actually the bottom because I flipped it) so I could raise it up a little more and provide plenty of clearance
4) I'm not going to use the supplied brackets, I have some angle aluminum that will work better and I already have to drill new holes if I want to use the Koyo threaded rivnuts.
5) Koyo didn't put rivnuts on the bottom holes, which is correct way to mount factory shroud, but I'm going to put some in so I can securely mount the bottom. The alternative I guess would be plastic push pins.
First two pics are before I made the modifications while I was test fitting...
Now for the cut...and how it helped with clearance...
Overall I am pleased with the kit. The instructions are well documented although I had to flip a piece on the back of the control module to get it to install properly on the shroud. They supply quality thick gauge wire and all the fasteners you need.
Again, if you have the tools to bend aluminum, you could probably just buy the fan, the flaps, and the control module separately and customize something that mounts direct to the radiator mounting points, but I think this solution is going to provide the flow I need at speed as well as the cooling I need in traffic.
have not tried it yet, but i like the Ford Mustang fan from about 2001. Part number RF-166. its the same size radiator core as the FC (should fit FB too). it has mounting ears on the side. its cheap, and comes in one unit.
Here's mine. Spal 16". Its not the superduper high out put one as i didnt want the current draw. Wired to an on/off/auto toggle switch and thermoswitch of my choosing. Custom rad based on a tii rad works fine. Been in 35-40c stop start traffic heaps of times. Never a problem.
previous set ups include an OE Tii rad and 16"davies craig mounted the same way,
and an ebay china FB rad with twin china 10" no shroud while i waited for my custom rad, again no problem.
Interesting thing was even the Radiator builders, Dandy Race Radiators, advised against putting a shroud on, saying it is not necessary even though it would have been very easy for them to do at minimal extra cost.
On a race car, no need for a shroud, I'll totally agree with that, no need for a fan for that matter if you shut it down coming off your cool down lap. But on a street car that will sit in traffic on a hot day, that's when the shroud improves efficiency.
I used the same logic as WANKfactor and have never used a shroud. My previous setup using custom radiator built by the same company as WANKfactor's, Race Radiator, combined with Davies Craig 16" puller (less output than Spal), and it would reduce temps by 5'C in under 30 seconds at idle. At most it would take 1 minute to to cool temps by 5'C in hot Melbourne summer days (40'C). If it can pull that much heat out of the system while the vehicle is stationary, and the shroud can only impede air flow when the vehicle is moving, then why would I use a shroud?
Shroud's help immensely if your radiator and/or fan is not up to the task, but if the fan and radiator are up to the tasks, a shroud won't be needed.
That said, I agree entirely with chuyler's post above about the considerations pro and con and the right solution will depend on the application.
Lots of good information in this thread. I just want to generally expand on the role of a fan shroud for cooling.
The shroud serves 2 main purposes:
It forces the fan to draw as much of its air as possible through the radiator. Drawing air through the radiator causes a pressure drop while the air already in the engine compartment requires no pressure drop to access, so the fan will draw a significant amount of its air from the engine compartment instead of through the radiator if it doesn't have a shroud.
It forces the fan to draw air through the entire surface area of the radiator. With a radiator shroud that spaces the fan off of the radiator the fan makes a low pressure zone that fills the entire compartment made by the shroud, so air can come from through the entire area of the radiator. A shroudless fan will only draw air from the surface area of the radiator that it covers, leaving a significant portion of the radiator receiving no air flow from the fan.
So essentially, a fan shroud causes the fan to draw more of its air through the radiator, and causes more of the radiator to be effective.
Some caveats to the above: If there isn't room to space the fan away from the radiator, you will get very little of benefit #1 and none of benefit #2 with a shroud, so shroudless is the way to go. The shroud will also reduce airflow through the radiator when the fan is not in use (such as high speed driving), so if it is exclusively a track car, shroudless is probably the way to go.
Definitely different strategies for race car vs street car. The common rule of thumb is that an OEM fan setup produces the air flow equivalent to driving at about 30-35 mph. So a race car under caution or in the pits or a street car in traffic or at stop lights needs something to augment the lack of air flow at those speeds.
All the tech that goes into fans and shrouds is about one thing...sound quality. A small electric fan right up against the radiator running at 2,000+ RPM sounds like a band saw. Use a PWM controller or at least a dual speed fan and you can reduce the sound by running lower RPMs as needed. Add a shroud and you can run even lower RPMs and produce the same cooling. Even if the shroud is just a cylinder of sheet metal between the fan's mounting flange and the face of the radiator, it will be an improvement in sound quality without any question of reducing high speed air flow.
03-06-19, 06:42 PM
