Fan blades 7 vs 8

[Ed]

I noticed that my 72 had a 7 blade cooling fan and my 73 had 8 blades. Does anyone know the reason for this? And which would provide better cooling?

[Bambikiller240]

IMO Given everything else remaining equal, more blades will move more air.

I believe that my fan (72) is also a 7 blade. It could be that as part of the remedy for the fuel vaporlock problems that were encountered w/ 73 240Z's, Nissan offered an uprated fan along with the electric fuel pump, insulation wraps to mitigate the problems. Could also be that a P.O. installed the "wrong" fan for a 1973 car.

MSA and Vic Brit list one plastic fan for 72-73, and a different plastic fan for 74-78 Z cars.

[2ManyZs]

The 8 blade fan was part of the recall to cure the vapor lock problems with the 73's.

Either one will work fine with a 3 or 4 row radiator. They'd work a lot better with a stock 2 row if you had a fan shroud.

I doubt there's enough gain with the 8 versus 7 to make much difference, the biggest difference would be either a larger radiator core or a shroud.

[JEFF]

I'm not sure 8 blades will move more air or not .. but it makes for a

quieter fan. It may take more power to turn it though.

- Jeff

[EScanlon]

I race R/C Boats (Nitro) and although I am a completely RANK amateur, I have learned that the different props one can use (2 and more blades) are usually graded based on the diameter and the pitch AND the amount of "wake turbulence" that a given prop will have at a certain RPM.

That's part of the reason why a more powerful engine won't necessarily go to a bigger prop, but rather a smaller with more pitch, because that allows the motor to max out the RPM curve.

Then you get into the curves of the blades from up by the shaft to the outer edge AND the curve from the leading edge (the edge that is actually biting into the medium) to the trailing edge.

In most automobiles, the blades are usually very plain even flat, the number of blades will not necessarily add to the volume of air being moved, unless the pitch is the same on both. The higher number fan will require more torque due to the larger volume going through. However, if you reduce the pitch when increasing the number of blades, you actually move the same volume of air but with less torque. You also usually pick up the advantage of having less wind noise.

In a car, when it is moving you actually eventually generate a pillow of air in front of your car. Air Dams attempt to nudge this pillow off to the side so that it won't generate uplift on the front of the car. They also help in directing air to the radiator core. The fan isn't so much to PULL air through the radiator when at speed, but rather to generate a lesser pressure area BEHIND the radiator than in front of it. That way the speed of your car will actually force the air through the radiator. At idle is the only time that you would really notice the difference in it's cooling ability.

At higher speeds, the fan needs to create enough of a pressure differential so that there isn't a "backlog" of air trying to go through the radiator. That backlog is nothing more than the development of another "pillow" of air.

The "exhaust" or escape of air that has travelled through the radiator out of the engine compartment is also an item that can cause overheating. Usually however, the bottom of the engine compartment is open to the environment and this is not an issue. If you were to cover the bottom of your engine area with a pan or a "splash pan" you might see a marked increase in the temperature of your engine.

2¢

Enrique