Too tight. As the engine moves on its' mounts due to torque the fan will hit the shroud. The opening in the shroud needs to be 1"-2" larger than the fan.
In addition to what PetesPonies mentioned, for good if not best efficiency, the fan should be positioned within 1" of the radiator surface. Also, 50/50% coolant is still a popular recommendation.
Not when using a shroud. The 1" rule is for no-shroud installations, which by the way IS a rule I learned from a Ford engineer. When using a shroud, the fan could be a foot from the radiator with no negative effect. Look under the hood of a Corvette sometime. Any Corvette.
Hmmm, a foot? While that may work in the case of early vettes. I've had good, if not excellent, success following the rule of "within and 1" of the rad surface and with the 50% of the blades within the shroud".
Hmmm, a foot? While that may work in the case of early 'Vettes. I've had good, if not excellent, success following the rule of "within and 1" of the rad surface and with the 50% of the blades within the shroud".
Here's an old engineering document on the subject. I've had it forever and I think it was put out by Caterpillar in the 70's.
There are probably a lot of necessary exceptions due to mounting and spacing constraints of engine / fan / shroud / radiator. Particularly to account for relative movement between them. But you could take these as general best practices and increase spacing where needed.
The number of blades won't do anything for you if the pitch of the blades is not optimal. Ever compare the pitch of the fan blades of the 4 blade HiPo fan againt the stock A code fan ? They are different. The HiPo fan will move more air even though it "appears" to be less substantial.
Many, if not all, propeller aircraft run at a steady rpm. The pitch of the propeller(s) is variable to speed up or slow down the airplane. The pitch of the blades is the single most important factor when determining how much air needs to be moved.
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