According to engineers at Modine radiator it takes at least 5HP to efficiently cool 300 HP.
Nissan Supercars seldom traverse rock filled washes or hours or steep grades in AZ summers. I continue using mechanical fans with
clutches as a first choice.
Ok so there are a couple of things to consider when designing a cooling system... Firstly any rule like "it takes 5hp to cool 300hp" is a very rough estimate but depends on a number of factors.
Here is what you need to consider.
Adding more cores returns diminishing results. Eg going from a single core to dual core ISN'T doubling your cooling capacity and going from dual core to 3 core certainly won't increasing cooling by 33%. There are some terrific engineering documents from industrial applications that list the efficiency gains (ill try and find the ones I've used in the past when i get home) but from memory going single to dual adds about 50% more cooling (not double) and going from dual to 3 core only adds like 10-15% (not 33%). (Again this all depends on core thickness, material type, air speed etc) They say that there is virtually no benefit to going 4 core (which is why you almost never see it).
The reason being is the first core will see ambient temperature. So it might be 90 degree coolant with 30 degree ambient temperature, that large differential allows a lot of heat to be exchanged. But the air temp going through the second core might now be heated to say 50-60 degrees so there is less of a differential which means less efficiency in cooling. Once the air gets to the 3rd core it should be pretty close to the coolant temperature so no real cooling effect left.
Now you can combat this by increasing the speed of the air through the radiator. If the air speed is much faster it has less time to exchange heat in the first/second cores so will be cooler in the third core. This is effectively the advantage on high powered thermofans moving air at a higher speed.
It also shows why a well designed/sealed shroud is absolutely critical, air will always take the path of least resistance. Mechanical fans have to have some clearance around the fan as the engine moves on the mounts, this means a lot of the air you are feeling being blown around is actually being sucked in around the gaps of the fan blade between the shroud. To do proper testing you need to get a air speed indicator and measure the air speed in FRONT of the radiator in a number of areas (divied the radiator up into a grid of 20 blocks and take an average from each block).
Electric thermofans can be designed with very minimal gap between blade and shroud. If its properly sealed against the core it means close to 100% of the energy used by the thermofan is moving air through the core (which is key).
Now the problem with all shrouds is they still struggle to get a 100% even spread of air movement through the radiator. Usually the air speed is highest directly behind the blade and minimal in the corners. (I measured air speed of 15kp/h directly in front of the blades and as low as 2kp/h in the very corner, and this is on a very high performance setup which is almost perfectly sealed with rubber/foam).
The problem with the standard 60 series radiator is you can't really run dual thermofan as its a very "square" radiator. Thats why all modern cars run a rectangle sized radiator where twin thermofan can be used. This gives much better coverage of the core resulting in higher cooling capacity compared to a single big fan.
So having said all of that, here was my design....
Standard front panel
Modified
As you can see i have considerably increased the size of the opening allowing a "rectangle" type radiator to be installed. This means i can run electric dual thermofans for a much more even spread of air flow over the core and being electric the shroud gap to blades is considerably less than with a mechanical fan.
So this is the radiator i choose...
And as you can see the twin thermofan fits almost perfectly.
Here is the bracket i made to bolt to the radiator which supports the thermofans. It is critical to get this "level" with the radiator to ensure minimal gaps.
Just to show the reasoning for the design this is the new heat exchanger for the airconditining at the front
The middle radiator is actually being used as the heat exchanger for the water to air intercooler (Its a 12HT turbo diesel)
And now the GTR radiator is mounted on the outside
Now it is close to the engine but does fit. A V8 should be considerably shorter than the I6. The main reason for using the GTR radiator is it has the inlet/outport on the same side which suits the 12HT
All those gaps around the edge will be sealed up (using various techniques of rubber strips and metal brackets). This should ensure all the air being drawn by the thermofans is through the radiator cores and not leaking in from the edges.
Now the reason i choose those thermofans is they are a VERY common choice here in Australia for burnout cars. So if they can cool a 750+ HP V8 on a skid pan for minutes at a time (Eg the engine constantly producing 500HP while stationary) then they shouldn't have any problems cooling an engine producing 50-150hp on the trail (I know its a much more powerful engine but you shouldn't be producing 500HP while actually 4wding, however even if you did it should support it).
So as I've said previously electric thermofans are BETTER PROVIDING they are designed and installed correctly. A simple SPAL bolted on WON'T WORK. A shroud bolted on with big gaps around the side WON'T WORK. You need an even spread to ensure airflow over the WHOLE core.
The other major advantage to thermofans with an inline assistance electric water pump is if you do start to overheat you can turn off the engine and keep the thermofans and electric water pump running to cool the engine down. With a mechanical fan you basically need to wait for the engine to cool down naturally (10+ minutes).
