Projects building fan shrould need info ASAP

I'm building a fan shroud for my 18.5 inch mechanical clutch fan. How large should I make the hole for safe clearance, and good air pull. I really need this info ASAP. Thanks guys.

 

1 inch clearance max all around should be sufficient. HRP

 

Closer is better, but you need to account for engine movement, frame twisting, etc. So I agree the 1 inch should work. If you can be sure to keep stuff from moving then you might get it down to 3/4 inch.

 

Be sure that your shroud only covers 1/2 of the fan blade or it won't pull nearly as much air as it could. The air being pulled through the shroud needs somewhere to go not just straight behind it. Don't ask me how I know this!

 

so were talking 3/4" off each tip? 1 1/2" total larger than the blade. Right ?

 

Yes, that is what I mean, 3/4 from the blade tip to the shroud. Engines can move around a lot vs the body, depending on your mounts and how much they give.

Also concur with the fan blade is about halfway in and halfway out. Look at stock fans and that is how they are usually. Elec fan is different, look at mech fan applications.

 

Remember the engine will move some...the shroud will remain stationary. HRP

 

Yeah I may try to install a torque limit strap. Like use in drag racing.

 

I used to adapt plastic factory shrouds for use in my stock cars. Not a whole lot of science behind it, make up aluminum brackets on the fly as well and get it in there. It did make for 20-30 degrees of reduced water temperature on a hot night.

My engines were chained down to limit how much they could move. I tried for the 1/2 the fan blade thing but depending on what was available I never saw any difference if the entire fan was encased.

Bob