Radiator fan shroud opening

I need some advice on my fan shroud for my 39.How much of the shroud opening should cover the fan assembly. Fan is 16" diameter. Here's a couple pics in mock up

 

If the fan is being mounted directly to the radiator you should not put a shroud on it. The fan can only pull from within its open area and your just blocking any airflow from the "unfanned" area.

The fan needs to be mounted at least an inch behind the radiator in order for the fan to pull from the corners.

Your shroud should seal up fairly tight to the fan and cover all of the finned part of the radiator. With an electric fan you should also punch some holes in the corners of the shroud to allow any air moving faster than the fan can pull to get out at highway speeds.

 

Free advice: If a fan shroud is attached to the same element as the fan (like yours, both are attached to the radiator or radiator support, the shroud should fit as tight as possible to the fan assembly. Some folks even use weather stripping to eliminate the gaps (leaks). IF the fan is on the engine and the shroud is on the radiator, you can have movement between the two when the engine torques. In that case, you will see the recommendation of leaving a slight gap between the fan and the shroud. For your case, zero gap is best.

Another tip is the shroud design. A shroud is a FUNNEL to funnel air from the radiator to the fan. IF the fan is mounted really close to the radiator, the funnel does not work well and the diameter of the fan becomes the diameter of the radiator (since the air cannot be sucked from the side areas). The desirable distance is for the fan to be at least 3" from the radiator so the funnel (shrould) has some depth.

The shroud should also fit tightly to the radiator to prevent leaks to make all the air go past the fan. Some shrouds will have small, hinged flaps on the sides of the fan to allow air to push the flap open at speed but NOT allow the fan to suck the flap open to bypass the radiator.

 

Thanks ,the fan brackets in the 1st pic space the fan about 9/16" from the fins.With the shroud I can mount it further back from the radiator surface.Thanks for the tip on drilling holes in the corners

 

You will see a lot of the new cars that have thin rubber 'flaps' on the fan shroud which allow air to pass through at highway speeds and then are sucked shut by the fan at low speeds.

I had a fan shroud built by Ron Davis (Lots of NASCAR radiators) for my pickup in the avatar and it incorporates these flaps. It uses a Lincoln MKVIII fan and works fantastic!!

 

Thanks guys back to the drawing board and garage.....

 

You might look at getting a Cooling Components fan and shroud assembly. I have one on my 47 Ford and it never over heats.

 

Best cooling investments I have made were CCI shrouded electric fans. I have used three of them with great results.

 

Got a CCI fan/shroud on my '40 Ford and 1940 Willys - the best and worth every penny....

 

Got the CCI fan/shroud on my 39 Ford.. Works as it is supposed.. John

 

39 DeLuxe shroud with lots of dust

 

think I'm going to copy your idea Mike. Thanks.

 

Some real good info!
Thanks for the heads up.

 

Thanks I will check out the CCI fan/shroud.Sometimes it's just as easy to spend the money.... especially with me putting in a new motor

 

You might check speedway also. they have the CCI fan/shroud cheaper that the CCI website.