Let's talk electric fan shrouds

How much room do I need to ensure enough flow?  How much wiggle room should I give the engine?  With my new mounts it doesn't move much at all when the engine is revved.  What else should I plan for?

The radiator to pulleys has 3.75" of clearance

Fan height is 2.75"

The fans will be offset so that the high points won't be directly in the way of anything.  

Doh!...never seen an electric fan shroud

PS put some socks on.  What has been seen....

Seriously though, check the V8 Pinto build on here.  You've got probably 3 times more room than he does.  

1)  As much room as possible

2)  I'm curious what the answer to this is.  My gut says 1/2"

3)  Not sure how you are forming this, but with sheet metal, the joggle distance is going to limit your minimum bend.

A 401 CJ said:

Doh!...never seen an electric fan shroud

 

PS put some socks on.  What has been seen....

Flip-flops with jeans? Son, you need some fashion lessons.

As much space as possible. Shoot for an inch of clearance to the core.

Consider putting in some bypass flaps. You can get the flaps themselves from SPAL. This allows the air to pass through the shroud when there's more pressure on the front than the back.

Engines don't tend to move fore/aft much, but I'd want to give an inch of clearance for it to rotate at the extremities.

How much room do I need to ensure enough flow? 

I've had conversations, with pictures and part in hand, with the folks at Ron Davis. The fan(s) can be right up to the rad without touching the core.  You do want / need to provide for as smooth / clear of an exit path as possible.

How much wiggle room should I give the engine?

As much as possible.

The fans can be almost touching the core, but then you only get flow through the parts of the core immediately in front of the fans. That's only about 50% of your radiator. The purpose of the shroud is to allow the fans to pull through the entire core, and in order to do that you need to have airflow between the shroud and the core. This is fairly easily proven experimentally and we've done those experiments.

As for exit path - you want to bring down the pressure behind the fans. This means getting air out of the engine bay via something like louvers at low pressure points. Engine bay air is high pressure and stagnant, and you're after the biggest pressure differential possible. This is particularly important for weak "slimline" fans that are chosen for their packaging ability.

Also, lots of oem shrouds have 'flaps' that allow air to bypass the fans (presumably at high speed if there is plenty of pressure differential) but still allow for the fans to create suction through the radiator if there is no 'ambient' pressure differential. 

Here are the flaps we use on our shrouds: https://www.summitracing.com/parts/spu-ix-30130012

The fans should be at least half the hub diameter's distance from the radiator, but more is better.

Some days I think about mounting the fans backwards, motor towards the radiator, so the blades are as far as possible from the radiator.

Shrouds are a funny thing, being asked to do contradictory things. At a stoplight, the radiator warms up and the fans come on. In that situation, a shroud that only allows air to go through the fan makes sense. At speed, say, a trackday, there's tons of air coming into the radiator, but now the same shroud is preventing maybe half of it from getting to the radiator. So, yes, simple flapper valves are a solution.

For me, I found that the fan keeps the engine sufficiently cool without a shroud so chose to run without. The idea is that when I really need cooling - at speed - the entire radiator is working. And yeah, getting the air to the radiator is no more important than getting it out. The outgoing hot air needs to be fed to an area of the car where the air pressure is less than the pressure on the inlet side of the radiator, else there's no flow.

Sounds like I'm going to be fighting for clearance from the pulleys and airspace from the radiators to the fans.

0.75" from the radiator to the fan might work?  Would leave a quarter inch from pulley to fan, but shouldn't be in the way of anything.  I'll mock something up from a sheet of plywood to ensure that. 

Looking at the necessary design of the shroud, I'm thinking I'll need some internal ribs to prevent it from flexing?

What thickness of aluminum sheet?  1/16"?

With the tight confines you have, I would NOT run a shroud.  The point of a shroud is so the fan can pull from the whole radiator.  Since you can't get the blades very far from the radiator core, a shroud would mostly block forced airflow, not assist the fan.

Yes, the fans will only be pulling from an area of radiator the size of the fan diameters minus the hub area.  The only way to avoid that is to move the radiator more forward so you can run a shroud.  (Half the diameter of the fan hub or more, so the fan can pull from the whole radiator.  Your shroud has to be shaped like a tent, not a blanket!)

Everything's a compromise, you know?

I love you guys, but y'all going overboard here.

First, electric and belt fans have to be viewed from different mindsets.  Belt fans use big blades spaced far apart.  They need to be set back from the radiator a bit for air flow, but also so they don't contact the radiator when they flex or when the engine moves under torque.  Electric fans can't really move as much air as a big belt driven fan, so they need a bit different engineering to function properly.  It's a little like the difference between a tiny engine that spins to 10,000 rpm to make 100 hp, versus a 5.0L V8 spinning to 3000 rpm to make the same 100 hp.

First, take a look at the electric fans you have and then compare them to a belt-driven fan.  Not only do those electric fan blades cover about half the real estate, the plastic grate behind it does as well.  Electric fans are great at being active flow-generators, but often times horrible at allowing passive flow.  Over on the hot rod forums, I wish I had a nickel for every time I heard someone's sob story about how they put this massive electric fan on their old car and now it overheats on the highway.

If you are doing a fan style like the ones you are showing, you will likely make things much worse with a shroud.  Now you will be forcing passive air to go through those mesh baskets.  You'll be effectively choking the passive airflow down to two small holes, each of them 50% blocked by plastic.  If you think about it, a belt fan might move 4000 cfm when you're sitting in the driveway revving the engine, and it might move 10,000 while you're on the highway because you have all kinds of space for free-flowing air.  The picture you show right now, if those fans can move 4000 sitting still, you might still be able to get that 10,000 cfm on the highway.  If you put a shroud on it and force the air through the fans, they might move 4000 sitting still.... and 4500 on the highway.

To get the flow from electric fans, you either need a shroud with the fans pulled away from the radiator and some mechanism for a TON of bypass for free-flow, or you mount properly-sized fans tight up against the radiator with no shroud so you have free space beside them for free flow.

But forcing all of the air to go through those strainers is a recipe for overheating.  The rated flow of a belt-driven fan and an electric fan are apples-to-apples when you're standing still.  When you're moving, the big difference is that belt fans allow almost free-flow of ambient air, whereas electric fans tend to reduce the amount of free flowing air.  The air being pushed through the grille is being slowed down by most electric fans.

It can be done, don't get me wrong.  OEMs do it all the time.  But they also have a million-dollar R&D budget.  I have confidence that you can do it too, you just might be in for a fair amount of trial and error.

Clearance from the pulley to the fan?  Not touching under torque.  I put an electric fan in a 50 Ford with a Viper V10 and had about 1/8" clearance from the pulleys to the fans.  The motor torques up/down/left/right, so as long as the engine torquing in those directions doesn't cause it to hit something protruding, don't stress.

I will also say this, and this is an extreme generalization.  Fans designed like the ones you pictured are generally intended for either supplemental cooling, or for low speed applications.  The basket blocks a ton of free-flow, but moves a good bit of air on its own.  They're designed for street rods, buckets, and parade queens that need to generate lots of flow on their own, but they don't care how much free flow they block on the highway because a '29 model T with a 350 is going to spend most of its time going from the trailer to the grass in the park for the car show.  They are also designed with blades that work best in low-clearance applications (minimal space)  If you pull them away from the radiator, the shallow approach angle of the blades won't work as well in free-air hanging from a shroud.  

For instance, here is a 3000 cfm electric fan that will probably work wonders for an overheating parade queen that never sees more than 35 mph.  Put it on the highway and it will likely overheat in 5 miles.

Here is a 3300 cfm electric fan that might work for the parade queen, but on the highway it never has to turn on because it has all that free-flow area.

But if you take the style of the first fan, and stick it in a shroud like the second fan, you're defeating the benefits of both designs.  The first fan gets whatever free-flow area it has because it DOESN'T have a shroud and air can flow through the radiator around it.  If you put style A inside shroud B, you're doing two things:  1) taking the shallow-pitch fan blades away from the radiator making them less effective, and 2) blocking half of the flow area with a basket.

Note that the amount of airflow on the highway is nowhere near as significant as you think it is, especially if you don't do anything to release underhood pressure. Point a strong fan at the nose of a car and try to get the radiator wet using a spray bottle. Most of the air is moving around the nose because going through the heat exchangers is difficult and air is lazy. I have seen too many highway cooling problems fixed with fan upgrades to believe that the fans are not contributing - and I've seen crap fans and shrouds (looking at you, Mishimoto) completely destroy the ability of a car to stay cool on track.

Are there OEM's that are installing electric fans in vehicles without shrouds?

depending on the engine you are running, you may not need shrouds.  My fiat 124 was one of the first cars with electric fans,  it had a simple single fan with only a "finger guard" to keep things out of the blades.  It could cool that notoriously hot running car while sitting at a light.

pres589 (djronnebaum) said:

Are there OEM's that are installing electric fans in vehicles without shrouds?

No.  Not counting auxiliary fans, like the pusher fans on some Mercedes, or the ones inside the clutch fan's shroud on some Jeeps and Dodge trucks.

They also are paying very close attention to the shape of the blades and of the blade shroud (the ring around the blades) for aerodynamic reasons.  The fans are closer to the radiators than ideal but they are still set as far back as space allows, and the blade shroud forms a smooth junction with the assembly.

I have never seen an aftermarket fan that was as well designed as an OEM fan.  My favorite is the '13 GT500 fan, which was available for only $200, pulled only 40 amps, and flowed something like 4000cfm.

I've found electric fans jammed into a mech fan shroud to work very well when there's enough space.  Despite both fans producing similar airflow in free air, the one I hacked into the clutch fan shroud on the BMW moves air through the radiator more evenly and produces far better cooling on the highway compared to the factory type fan shroud on the Jeep (which is basically the well liked Taurus / Mark VIII e-fan in a different shroud). 

BMW setup I put together is shown here (factory E90 3 series e-fan in the stock shroud).  See the second picture for fan to water pump clearance.  Even in a car with pretty squishy motor mounts, that hasn't hit. 

The old Ford taurus fan + shroud also used to be a well known ticket to massive airflow for people converting to electric.

Rarely does aftermarket compare, but often aftermarket has much tighter conditions to deal with as well.

Like keith mentioned earlier, do not underestimate the impact of engine bay airflow on your cooling capacity!  The brute force more radiator + more fan approach is often unwarranted.  Take a look at what well prepped track cars do to deal with airflow at speed.

Keith Tanner said:

Note that the amount of airflow on the highway is nowhere near as significant as you think it is, especially if you don't do anything to release underhood pressure. Point a strong fan at the nose of a car and try to get the radiator wet using a spray bottle. Most of the air is moving around the nose because going through the heat exchangers is difficult and air is lazy. I have seen too many highway cooling problems fixed with fan upgrades to believe that the fans are not contributing - and I've seen crap fans and shrouds (looking at you, Mishimoto) completely destroy the ability of a car to stay cool on track.

Totally agree when you're blowing a fan on a car.  On the road it's a whole different thing.  High pressure in front of the grille and cowl and low pressure from the air moving under the vehicle (and the boundary layer on the road) make for a LOT of airflow through the radiator.  In fact, it's why many OEMs now use weatherstripping under the hood.  It's not for noise, (although it might help) it's to take advantage of the low pressure under the car and make more air flow through the grille.

My old Impala SS didn't have shrouds.  It had two that looked like this.  Same thing was on the 9C1 caprice which was designed to sit and idle for hours at a time with a big all-iron V8.

Curtis73 (Forum Supporter) said:

Keith Tanner said:

Note that the amount of airflow on the highway is nowhere near as significant as you think it is, especially if you don't do anything to release underhood pressure. Point a strong fan at the nose of a car and try to get the radiator wet using a spray bottle. Most of the air is moving around the nose because going through the heat exchangers is difficult and air is lazy. I have seen too many highway cooling problems fixed with fan upgrades to believe that the fans are not contributing - and I've seen crap fans and shrouds (looking at you, Mishimoto) completely destroy the ability of a car to stay cool on track.

Totally agree when you're blowing a fan on a car.  On the road it's a whole different thing.  High pressure in front of the grille and cowl and low pressure from the air moving under the vehicle (and the boundary layer on the road) make for a LOT of airflow through the radiator.  In fact, it's why many OEMs now use weatherstripping under the hood.  It's not for noise, (although it might help) it's to take advantage of the low pressure under the car and make more air flow through the grille.

I knew that would get mentioned :)

There's a lot less pressure on the top side of the hood than in the engine bay at speed. You can still pull a lot of pressure out of the underhood area with louvers and this will improve airflow across the rad. Helps with downforce, too - you'd rather have that air replace the low pressure on top than underneath.

One of these days I need to tuft the backside of a rad and stick a GoPro under there.

I totally agree that higher speed does not necessarily mean more flow through the radiator. The ducting in front of the radiator (collecting high pressure air and making it's only escape to be through the radiator) and the ducting after the radiator (shrouds plus making sure there is lower pressure after the fan) will make a massive difference. 

Also, I think OP is putting this on a truck, so high load does not necessarily come only at high speeds like we are used to thinking with racecars. 

In this situation though I'd be temped to go no shroud (simplify) first and see if it overheats in OPs use cases.