Good luck. Let us know if you make any progress.

Buy a throwaway stock hood and mount that on. I bet your "vents" are actually pressurizing the engine bay

Also look up the hardware store mixing tray mod. There's a thread on it here, it'll give you a huge head start on properly sealing the rad

Could also try a lip on the front edge like the singular.

Fans do nothing other than create restriction once the car is moving more than about 35 mph. The only reason you need a fan on a track car is so that you can idle it on grid.

--Ian

I can assure you the speed that it becomes a restriction depends on how much air it moves and the type of blade. At 60mph mine will kick on, drop the temp to the control and shut off. The broad curved blade type is not as efficient. It also depends on how thick the rad core is or if there is an AC condenser.

No. If he was overheating in traffic or after he pulled into the pits, yes. That's not the issue here.

40mph is 3520 feet per minute. Assume a spherical cow and a duct size of 1' x 1', giving you 3520 cubic feet per minute through the duct. If the duct inlet or outlet is blocked, you clearly won't get that 3520 cfm. Putting a fan in the middle of that blocked duct isn't going to do anything, the duct is still limited by how much it can take in or let out. Unblock the duct.

You're not taking into account the restriction of the rad. I have logged this several times when I was figure out my PWM map. On a hot day cruising down the freeway my fan will turn on and reduce the coolant temp. Your theory is flawed.

The restriction of the rad is the same for both a fan-backed radiator and a no-fan radiator. Thus it can be ignored.

I'm not sure what you saw in your data logs, but it's probably pointing out that your setup isn't the well-ducted, well-vented target being described here.

The pressure in front of the radiator is not the same as the pressure behind. The radiator is a restriction which reduces the air speed and volume. The contribution of the fan is relative to the post pressure since this is a puller fan. If it is powerful enough to reduce the pressure behind the radiator it will increase the amount of air mass that goes through the radiator.

What I have experienced is that at 20mph if a fan of X capacity will reduce the temps then a more powerful fan will have a similar effect at a higher speed. Because this is a mass vs time or volume vs time phenomenon it might be a cubed factor which may make it impossible to incorporate a powerful enough fan to achieve this effect at substantially higher speeds and there will be a point of no return. I have tested 5 different fans, three different radiators and the result was a high cfm larger fan can be a benefit. Also the greater the restriction the greater the pressure drop and the more effective the fan is. Maybe in my setup it is actually very well ducted and the IC, radiator and ac condensor are the limiting factor.

I guess I'm deep in the litter box on this one. My previous explanation was not good, and I take full responsibility for that. After a bit of research and reading info from the fan manufacturers I believe I can convey my point. One quick google search revealed that there is a general speed at which the fans are not contributing to the cooling. This is a good way to describe the phenomenon and I did make this claim in an early post, but it is a generalization. This is a variable that will be different for every application.

The speed is determined when the air pressure at the back of the radiator core is greater than the negative pressure developed by the fan. The pressure at the back of the core is affected by the resistance of the core and what is in front of it. The shape and thickness of the components can have a profound effect on the air flow and pressure at the back of the radiator core. This is why vehicles with AC cond's, oil coolers and intercoolers etc will be more dependent on the fan. It also means that the fan will contribute to the cooling at a higher vehicle speed relative to a vehicle with just a radiator. The difference might be 25mph for just a radiator and 40mph for a vehicle with many restrictions.

The fan manufacturers do not like to use CFM to define the effectiveness of the fan, but rather the current draw. The logic is that the reduction pressure or suction is the main factor of its effectiveness. A more powerful fan will generate a greater pressure drop which will extend it's contribution. The fan manufacturers consistently recommend using the most powerful fan that will work for the application. This was true for me with my Miata. I went from 2 small thin compact 12" fans to one deeper much more powerful 12" to an even more substantial 14" and every time cooling performance improved.

Above this diminishing return vehicle speed my coolant temps will increase when the ambient temps are relatively high. The fans which are programmed to turn on by temp with no consideration for vehicle speed will decrease the coolant temp. This appears to be extraordinary and a source of disagreement. I have read several sources that claim that the straight blade higher efficient fans are less of a restriction when they are running. As much as 10-20% and this must be the cause of the cooling when they turn on. I have witnessed broad curved bladed fans that are design for low noise actually increase the restriction when they are on. The fan that I'm using has a hybrid blade that is thin and straight. The hybrid blade has pitch close to the hub and towards the tips changes to an airfoil shape. These are supposedly more efficient. Our application can be a challenge to cool especially for dual duty and track cars. Hopefully this is of some value.

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A shot in the dark.
A friend was having huge trouble with cooling his race car (12 A rotary RX7). He tried many things, ducting, removing thermostat, higher pressure rad cap.
He had a nice aftermarket Aluminum rad, but once he had it tested at a shop, he was told it was not flowing the coolant properly. It had become blocked.
He replaced it, and the problem was solved.

Perhaps consider the hardware you have in place, and how to test it.