I am wanting to place 2 7.5" Spal fans at the rear of my street tail. I am not sure of direction... should I order "push" or "pull"? Any recommendations on how to wire so that they are controlled to come on at a particular temperature?
Spal Fans
- Thread starter mcfling
- Start date
According to this website you will need a pusher (Spal calls it a -34S blower):
Spal Usa Automotive Electric Radiator Fan 7.5 Inch Low Profile Straight Blade 437Cfm Puller
This website also has thermoswitches and wiring diagrams. Though if you are just thinking of it turning on a certain underhood temperature rather than engine water temperature, then I would look for a bi-metallic temperature switch and use a relay.
Spal Usa Automotive Electric Radiator Fan 7.5 Inch Low Profile Straight Blade 437Cfm Puller
This website also has thermoswitches and wiring diagrams. Though if you are just thinking of it turning on a certain underhood temperature rather than engine water temperature, then I would look for a bi-metallic temperature switch and use a relay.
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http://www.summitracing.com/parts/flx-31147/overview/
To control the fans.
A push fan mounted inside the tail to send air out of the engine area.
To control the fans.
A push fan mounted inside the tail to send air out of the engine area.
Ian Anderson
Lifetime Supporter
Hi
Couple of questions
Is your under body sealed - if not will the fans not just suck air from around and under the transmission and blow that out the back? - leaving the majority of hot air around the engine?
Surely mounting the fans at the front of the engine bay and blowing rearwords would be more efficient in removing heat?
I fitted some 4 inch 250cfm bilge room fans in my GT40 and manual switch each side of the front of the engine.
In traffic the bulkhead heats up but turn the fans on and you can feel it cooling - sucks the cool air through the side scoop area
Ian
Ian
Couple of questions
Is your under body sealed - if not will the fans not just suck air from around and under the transmission and blow that out the back? - leaving the majority of hot air around the engine?
Surely mounting the fans at the front of the engine bay and blowing rearwords would be more efficient in removing heat?
I fitted some 4 inch 250cfm bilge room fans in my GT40 and manual switch each side of the front of the engine.
In traffic the bulkhead heats up but turn the fans on and you can feel it cooling - sucks the cool air through the side scoop area
Ian
Ian
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Ken Roberts
Supporter
Here is a robust controller to consider. It can be used with typical GM sensors. You could use a IAT sensor to monitor the engine compartment temperature and then use it's two relay controllers to turn on the two fans at different temps or the same temp. Download the manual after you click on the link (at the bottom of the page) to read more about its operation. The last page of the downloaded manual lists the GM sensors that can be used with it.
https://www.lingenfelter.com/sites/...1 Temperature Based Relay Controller v1.0.pdf
https://www.lingenfelter.com/sites/...1 Temperature Based Relay Controller v1.0.pdf
As I hear what is being said, my interpretation is that if you are at the rear of the body work you will be at a low pressure point just after the body panels. A puller fan would get more benefit from that zone than a pusher(for the cooler). That is the way I have mine wired. If your goal is to expel heat from the engine bay I would suggest the 5' fans at the bottom(or vented section) of the front engine bay blowing into the bay(high pressure zone). They can be controlled easily by a thermostat and can help eliminate engine soak and overheating of the fiberglass body, if they have an off timer relay that allows the fans to run for a few minutes after shut down. Chuck and I both have them on our cars. The best are found at Waytek,com.Welcome to Waytek
They have both fixed or adjustable, works great, depending on what you like. When I ordered mine some time ago there was only the 0-10 minute adjustable available. I set it at or about 3 minutes and it works well.
3-mins--fixed: Solid State Relays | Timer Relays | Waytek, Inc
SOLID STATE OFF DELAY TIMER RELAY 12V 15A 0-10 MIN INPOWER - 75543
Bill
edit: I did some quick research and found that the pullers are more efficient than the pushers, especially if they use a shroud in a high pressure setting. All the electric fans you see on factory cars today are pullers. Fans are most beneficial at low speeds or at idling, the pushers can actually block flow at highway speeds.
They have both fixed or adjustable, works great, depending on what you like. When I ordered mine some time ago there was only the 0-10 minute adjustable available. I set it at or about 3 minutes and it works well.
3-mins--fixed: Solid State Relays | Timer Relays | Waytek, Inc
SOLID STATE OFF DELAY TIMER RELAY 12V 15A 0-10 MIN INPOWER - 75543
Bill
edit: I did some quick research and found that the pullers are more efficient than the pushers, especially if they use a shroud in a high pressure setting. All the electric fans you see on factory cars today are pullers. Fans are most beneficial at low speeds or at idling, the pushers can actually block flow at highway speeds.
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I've always understood push fans to be more efficient due to the fan motor body not being a physical impediment to the high flow side. In other words, the entire blade face is effectively pushing air, not just that which sticks out beyond the fan motor body. Seems to make sense to me, but I have no idea if that is technically valid/accurate
Seems like pusher fans mounted inside the rear clam shell is the simple solution
Seems like pusher fans mounted inside the rear clam shell is the simple solution
Howard Jones
Supporter
Fans draw air from the point directly in front the blades creating a low pressure spot directly in front of the fan. This very small low pressure area will be refilled from the shortest distance possible. Unless you restrict flow to the area directly in front of the blades with ducting then they will be very inefficient in cooling a large area with multiple routes of refill. In the case we are talking about a shroud would need to enclose the inlet side of the fan and then a ducting arrangement would need to be run to the point that you want to extract the hot air from.
This is why it is so important to duct the radiator fans sealing them to the radiator at the front of the car. This forces the fans to draw all the airflow through the radiator.
More than likely a fan mounted in the hole at the back of a GT40's bodywork for example will simply draw air up from the bottom (least restrictive inflow source) and through the fan to behind the car. This won't serve to cool the engine room much if at all.
A better idea would be to open a spot on the bodywork that has a high pressure area directly adjacent to it and duct the inflow to the spot you want to cool. This can be done with a simple scoop or NACA ducts. I spent a lot of time considering this with my SLC engine room and came to the conclusion that adding scoops on the top of the engine cover, sealing the bottom, and and opening the rear of the engine bay so that airflow was THROUGH the compartment was the best way to go. I also opened up the side scoops to add inflow along the sides of the engine and out the back to further increase the overall total airflow through the engine room. I am over pressurizing the compartment with outside cooler air and extracting it out the back into a low pressure area behind the car.
The problem will be a standstill if I have one. I have been thinking about a fan on the bottom of the car with a flap that closes at speed but since this is a track car it won't spend much time standing still.
Small fans 5-8 inch's in diameter can't move enough air to do much good considering how much heat is being generated. On a street car I would leave the bottom open, and maybe vent the top so that the chimney effect would ventilate the engine room when stopped. One moving the open bottom will flow plenty of air to cool the compartment.
Sorry to burst the fans at the back bubble but money spent on a oil cooler is a better idea.
This is why it is so important to duct the radiator fans sealing them to the radiator at the front of the car. This forces the fans to draw all the airflow through the radiator.
More than likely a fan mounted in the hole at the back of a GT40's bodywork for example will simply draw air up from the bottom (least restrictive inflow source) and through the fan to behind the car. This won't serve to cool the engine room much if at all.
A better idea would be to open a spot on the bodywork that has a high pressure area directly adjacent to it and duct the inflow to the spot you want to cool. This can be done with a simple scoop or NACA ducts. I spent a lot of time considering this with my SLC engine room and came to the conclusion that adding scoops on the top of the engine cover, sealing the bottom, and and opening the rear of the engine bay so that airflow was THROUGH the compartment was the best way to go. I also opened up the side scoops to add inflow along the sides of the engine and out the back to further increase the overall total airflow through the engine room. I am over pressurizing the compartment with outside cooler air and extracting it out the back into a low pressure area behind the car.
The problem will be a standstill if I have one. I have been thinking about a fan on the bottom of the car with a flap that closes at speed but since this is a track car it won't spend much time standing still.
Small fans 5-8 inch's in diameter can't move enough air to do much good considering how much heat is being generated. On a street car I would leave the bottom open, and maybe vent the top so that the chimney effect would ventilate the engine room when stopped. One moving the open bottom will flow plenty of air to cool the compartment.
Sorry to burst the fans at the back bubble but money spent on a oil cooler is a better idea.
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Howard,
I agree with almost all that you have said. My fans at the rear are simply pulling air through my oil cooler into the low pressure area at the rear. They aren't there to cool the entire area. I don't mind where the air is coming from as long as I get it through the cooler(s). I guess since the underside of the car is a negative pressure zone it would suck the air up into any space that is open like the engine bay. I am a fan(no pun intended) of putting the air flow in front of something hot like an exhaust or engine rather than pulling it from behind. I think that in having the small fans in the front portion of the engine bay, you are directing that air up into the engine bay's front section. Mine actually pull air from the sections just to the side of the fuel tanks, so I don't know if that is a high or low area. Their air flow is not that great. Something like 300+cfm apiece.The natural forces of pressure gradients should help the air direct its flow over and through the exhaust pipes and along the upper surface of the rear clip. My prime objective of the front bay fans is to negate some of the heat going to the fiberglass from the exhaust, which is at its max when standing still or idling along. I have seen it bubble the paint more than once. Since I drive mine more on the street, I need that effect to save the paint job(at least I hope that is what I am doing). My exhaust has a good bump up near the rear of the engine and that is the offending area. I need to add more insulation to all of that area of the clip. The air flow is to keep the heat moving to the rear and eventually out the back. I had considered the thought of adding a louver at the bottom edge of the front portion of the engine bay to direct some of the flow up and into the engine bay to assist moving the heat. With such low ground clearance in that area(over bumps), I am afraid of road contact. I may have to rethink some of this and consider something like moving the fans up to the top of the engine bay. Hmmmmm.
Bill
I agree with almost all that you have said. My fans at the rear are simply pulling air through my oil cooler into the low pressure area at the rear. They aren't there to cool the entire area. I don't mind where the air is coming from as long as I get it through the cooler(s). I guess since the underside of the car is a negative pressure zone it would suck the air up into any space that is open like the engine bay. I am a fan(no pun intended) of putting the air flow in front of something hot like an exhaust or engine rather than pulling it from behind. I think that in having the small fans in the front portion of the engine bay, you are directing that air up into the engine bay's front section. Mine actually pull air from the sections just to the side of the fuel tanks, so I don't know if that is a high or low area. Their air flow is not that great. Something like 300+cfm apiece.The natural forces of pressure gradients should help the air direct its flow over and through the exhaust pipes and along the upper surface of the rear clip. My prime objective of the front bay fans is to negate some of the heat going to the fiberglass from the exhaust, which is at its max when standing still or idling along. I have seen it bubble the paint more than once. Since I drive mine more on the street, I need that effect to save the paint job(at least I hope that is what I am doing). My exhaust has a good bump up near the rear of the engine and that is the offending area. I need to add more insulation to all of that area of the clip. The air flow is to keep the heat moving to the rear and eventually out the back. I had considered the thought of adding a louver at the bottom edge of the front portion of the engine bay to direct some of the flow up and into the engine bay to assist moving the heat. With such low ground clearance in that area(over bumps), I am afraid of road contact. I may have to rethink some of this and consider something like moving the fans up to the top of the engine bay. Hmmmmm.
Bill
Howard Jones
Supporter
This stuff is so good that I would damn near promise that the paint on the other side if it will never get hot enough to be damaged. I have taken a leftover piece laid it right on the headers when the engine is full chat hotter than hell and leaned on it with my full body weight using my bare hand to brace myself. It took a good 30 sec before I even felt enough heat to start hurrying up what I was doing.
Really good stuff and worth the money. I have my entire upper inside of my GT40's rear clip coved with it. It has held up for more than 10 years without any change in effectiveness. Paint on body is like new. NO HEAT DAMMAGE.
https://www.pegasusautoracing.com/productdetails.asp?RecID=7267
https://www.pegasusautoracing.com/productdetails.asp?RecID=6854
Fans will work very well to force air though a cooler. It's the huge heat load coming off a hot engine in a enclosed engine room that a couple of relative small fans will never keep up with unless they can really push huge CFM and the airflow is properly directed and managed. Any fan that could would draw a LOT of power to do so.
Maybe NACA ducts in the floor oriented to draw air in from under the car would do some good but with it comes all the road debris and water in the rain.
This the same path I went down and ended up with the previous posted solution. Other than good air flow through the engine room, heat shields where necessary and things like ceramic coating the headers there really aren't many alternatives.
Really good stuff and worth the money. I have my entire upper inside of my GT40's rear clip coved with it. It has held up for more than 10 years without any change in effectiveness. Paint on body is like new. NO HEAT DAMMAGE.
https://www.pegasusautoracing.com/productdetails.asp?RecID=7267
https://www.pegasusautoracing.com/productdetails.asp?RecID=6854
Fans will work very well to force air though a cooler. It's the huge heat load coming off a hot engine in a enclosed engine room that a couple of relative small fans will never keep up with unless they can really push huge CFM and the airflow is properly directed and managed. Any fan that could would draw a LOT of power to do so.
Maybe NACA ducts in the floor oriented to draw air in from under the car would do some good but with it comes all the road debris and water in the rain.
This the same path I went down and ended up with the previous posted solution. Other than good air flow through the engine room, heat shields where necessary and things like ceramic coating the headers there really aren't many alternatives.
Howard,
Other than the high temp spray did you use anything else to hold the fabric onto the rear clip like click bond fasteners etc. I have sanded my my underside(tray area) due to the residue of the previous insulation/glue that I had to remove.The combination of the rough fiberglass and the glue made it necessary.
Bill
Other than the high temp spray did you use anything else to hold the fabric onto the rear clip like click bond fasteners etc. I have sanded my my underside(tray area) due to the residue of the previous insulation/glue that I had to remove.The combination of the rough fiberglass and the glue made it necessary.
Bill
Ditto that.
Howard, how did you affix that Thermo-tec shielding to the shell? Wondering if there's a high-temp adhesive that will work here rather than mechanical means to hold it in place.....
Thanks
Howard, how did you affix that Thermo-tec shielding to the shell? Wondering if there's a high-temp adhesive that will work here rather than mechanical means to hold it in place.....
Thanks
