Fan design and any improvements?

[skiday]

I have just stripped my heater box and matrix, which turns out is made of rust! Anyway, I couldn't help but think that the reason the heater blows like an asthmatic fly is because the blades on the fan wheel have no direction. In the following diagram they are like fig.1. Surly they should be like fig.2 in order to create any decent air pressure? Has anyone addressed this problem with improvements? From the catalogue it looks like the series 3 has angled blades, is that so?

[kingzetts]

If you research this subject on Jag-lovers you will find that quite a few people have used the heater fan and motor from a Pontiac Fiero to increase the airflow. I have just done this mod myself and it makes a huge difference to the amount of air coming through the vents, and is an easy mod to carry out. I was provoked to do it by a journey to my sister-in-laws last October which was damp - and the standard fan really was not up to the job of clearing the screen.

The fan is larger in diamater than the original and just able to fit inside the fan chamber. It is also deeper top to bottom and eliminates a substantial gap between the top (or bottom depending on where exactly it is mounted on the motor shaft) of the original fan and the fan shroud and presumably prevents air simply bypassing from the delivery to the inlet side of the fan.

The fan blades are also swept in exactly the way you propose would be helpful.

The installation requires cutting the hole in the bottom of the heater box to a larger diameter, removing a ring of metal, to allow the larger fan to be inserted into place. Cut off the existing studs to which the old heater base plate is bolted, drill four new holes to suit the holes in the Fiero motor baseplate, which can either be tapped to take suitable bolts (I used M5 bolts) or could use large self-tapping screws. It really is one of the easiest mods to do.

I did look to see if I could find a European donor car for this mod. After a lot of looking around I found that Fiat Punto Mk2 fans are the same size as the Fiero fan and have the blades swept the same way and turn the same way. However like nearly all modern cars the fan motor is housed in a moulded plastic housing which then is clipped into the fan housing, and I was unable to figure out an elegant way to attach the fan to the E-type housing. I therefore simply bought a Fiero fan and motor off US Ebay which arrived in about 10 days, and cost around ?50 delivered including import duties, and it really fits very nicely.

The extra performance of the motor and fan can be shown by looking at current draw. My "standard" motor (actually a modern Clayton replacement) with the standard fan drew about 3.7A, while the Fiero motor and fan draws 8A.

There are two electrical issues to consider, again these are dealt with on jag-lovers. First, if you want a low-speed, you need to procure a replacement heater resistor. The e-type heater resistor is designed to work in series with the standard motor and has a 2.5 ohm resistance. The Fiero motor has a resistance more like 1.5 ohms and a 2.5 ohm series resistor simply slows it down too much. Also the power burn across the resistor is much higher than standard and the standard resistor gets VERY hot. I bought a small selection of power resistors with inbuilt large aluminium heat sinks from RS Online and played around with resistance to get a slow speed which seemed to blow about the right amount of air. I found a 1 ohm resistor about right, but 0.75 or 1.5 ohms were also an option.

Second, I decided I wasn't comfortable putting 8A through the fan switch on the dash or indeed pulling it off the standard dash fuse which also carries the wipers. So I installed a pair of relays with a direct fused feed off the battery, with the relays switched by the low and high speed settings on the dash switch, to power the fan.

If you do decide to buy a Fiero fan from the US, don't make the mistake of getting one from another similar-age GM vehicle which is advertised as fitting the Fiero. This is true of the motor itself, but the fan cage can differ in size in different vehicles and you need the right size of fan, not just the motor, so unless you can find out the cage size for sure, best to buy one actually off a Fiero. Also check with the seller that hte fan cage comes with the motor - some just supply the motor without the fan itself.

[Heuer]

The fans that SNG sell are much as in your drawing - a series of angled foils around the circumference of the drum like a Dyson. It is a direct replacement and seems to work OK and has the benefit of not requiring major surgery to get it to fit.

[kingzetts]

By the way, the fan rotates the other way to that you've indicated in your sketch. The fan rotates counterclockwise viewed from above, and the blades are swept the same way - by which I mean the outer edge of the vanes "leads" the inner edge of the vanes, or it is as if the outer rim of a straight vane fan has been twisted counterclockwise relative to the centre.

[skiday]

Thank you ?kingzetts? for such a lengthy reply. Very interesting about the Fiero fan, but if SNG makes a fan with angled blades as a direct replacement then that is the obvious choice.

At the time of making my diagram I did not know which way the motor spun, but if it is the other way, then if the blades are in the same orientation as my diagram, surly that would be the wrong way? A propeller only works in one direction, the forward edge leads and the trailing edge follows. I can see from the photo of SNG's fan that it looks like fig.2, but if it spins counterclockwise I can't see how that draws air from the centre and pushes it to the outside, I would have thought it would do the opposite.

[kingzetts]

Empirically I can assure you that the fan does rotate counterclockwise and that with blades as per your drawing and as per the photo David has provided the motor draws more current (and hence is drawing more power and flowing more air) than if it turns clockwise. I checked this on the bench by reversing motor polarity to change direction of rotation of 3 different swept-blade fans. Current draw, noise level and "hand test" of air movement all confirm this. Also I found that as installed in modern cars the blades are always swept forward in the direction of rotation, not backwards.

[skiday]

I'm really sorry if I'm being daft here, but it still doesn't make sense to me. OK, so the motor draws more power if it goes counter clockwise and all modern cars have the blades swept forward, but it all comes down to the direction of airflow. In the e-type heater box we are taking air from the centre of the fan wheel and pushing it to the outside of the wheel yes? From the diagram I made of my desktop fan one can see the blade scooping the air from behind the fan and propelling it forward, but as the heater blades are oriented the other way, surely that pushes the air from the outside of the wheel to the inside, which is the opposite of what we want isn't it?



I can imagine that it would be a more common and better design for the air to go from the centre of the wheel to the inside of the car, but that's not the flow direction for the E.

[kingzetts]

You are correct that air is being moved from the "eye" or centre of the fan wheel to the outside. Leaving all the theory aside, the reality is as I have described it - all the modern cars I looked at move air in the same way, from the eye of the wheel to the outer rim, and all use blades swept forward in the direction of travel.

A desk fan or an aircraft propellor is in fluid dynamic terms a different duty to the heater fan. Desk fans and propellors are axial fans - that is, they are designed to move air in a straight direction from in front of the blade to behind the blade. Squirrel cage fans such as car heater fans are hybrid axial-radial fans, designed to receive air axially into the eye of the cage and send it out through a 90 degree change of direction along the radius of the cage. As such it is perhaps understandable that the optimum blade shape is different.

My time studying fluid dynamics is too long ago to try to argue from the theory, and I initially expected the same thing as you namely that the blades would be best swept in the other direction, as this is the way the blades in axial/radial centrifugal liquid pumps are arranged. However what got me doubting this was the practical discovery that modern cars have the blades swept forward, which I then verified experimentally gave a superior result.

For what it is worth, a cage fan with the blades swept the other way (ie swept back) still pumps considerable volumes of air, just not as much as with swept-forward blades.

[skiday]

I spoke to my mechanic and he helped me to understand things better, that it is more centrifugal force that is pushing the air outwards. Plus, when looking at the box that the fan sits in, the fan is not central, and that is obviously important. On the way home from the garage I saw a cylindrical wind turbine, which is the similar, but in reverse. The wind (away from me) pushes the wheel (with the same orientation of vanes) around in a clearly obvious direction (clockwise) because it catches the left side but flows past the right side. Reverse the direction of the wheel, power it, and it would push the air towards me (like I'm standing where the heater matrix would be). It's really quite complicated, but I think I get it now - Thank you.

So the practical experience is, from those that have bought the SNG wheel with angled vanes, that airflow is increased by how much? I'm trying to imagine how much extra air is worth ?40.

Wouldn't a fan, the type you have cooling your computer, fitted into the grill above the wheel where the box meets the ducting box on the bonnet, be a way of boosting air pressure?

[kingzetts]

I can entirely understand if people prefer not to go to the extent of something like the Fiero fan/motor and stick to something which uses the stock motor and stock heater box.

But....think of it this way. To move more air, you need to put more power into the job and all other things being equal (such as speed of rotation and blade efficiency) a larger fan will move more air than a smaller one.

The original fan is 5" diameter x 2 3/8" deep. The Fiero fan (which is about the largest which will fit inside the heater box) is 5 3/4" diameter and 2 3/4" deep. The SNG fan, since it fits the unmodified airbox, will be 5" diameter but may be deeper than standard (I don't know). My money is on the larger fan to move the most air, and I don't believe any greater efficiency in the SNG swept blades compared to the Fiero swept blades could overcome the size difference.

With the Fiero fan I get a strong airflow over the screen even with the footwell vents open, exactly as reported by others on Jag-lovers. I have no equipment to measure the airflow increase, but a good indication would be the current draw on full speed of the various setups - standard motor and fan, standard motor and SNG fan, Fiero motor and fan. I measured the standard fan in the heater box (but with the box off the car) to draw 3.7A, while the Fiero fan, with the heater installed in the car, draws 8.5A. If anyone has the SNG fan and cares to measure the current draw we can complete the comparison.

In my opinion the Fiero mod is not major surgery (others may disagree). It requires 30 minutes work with a Dremel to enlarge the hole in the base of the heater box by about 3/8" all round, another 30 minutes to tap mounting holes to suit the new baseplate, and another hour or so to make the electrical mods which can all be done invisibly and reversibly.

The whole thing cost ?80 - ?70 for the Fiero fan from the US (including ?18 import duty, which I've found sometimes Customs charge, sometimes they don't), ?10 for the heater resistor, relays and wiring, and some black paint I already had on the shelf to tart up the Fiero motor. Here's a pic of the installation - all the changes are hidden underneath the heater, and the original fan can still be bolted back in place pretty easily if you really wanted to go back to standard.



Each to his own, of course, but as my car already had a 5-speed box and later 4.2 brakes with Zeus calipers when it came to me I did not start with an "original" car in the first place.

[Heuer]

I fitted the SNG fan (I have an original one on the bench as well) but I have to say I rarely use it as I have an OTS so either the hood is down, the windows are open or the significant gaps allow plenty of air in. Never got around to comparing original vs SNG as I only recently managed to find a good Jaguar one. As far as I can tell the fan is only of real use in slow moving traffic to make up for the lack of ram-air but if the Fiero mod makes for a better driving experience ....................

[kingzetts]

David,
Like I said each to his own. As I intend to use the car in all weathers except salt on the road, and as I have already had a bad experience being unable to clear the screen with the hood up on a cold, dark, wet and lengthy journey, I simply want to have the option of decent airflow to the screen on those perhaps rare occasions when I need it.

[Heuer]

John

The more I read about the conversion the more it intrigues me! Any chance you could cut 'n paste your description, add a bit more detail and put it a thread in the 'Upgrades' part of the Forum?

[kingzetts]

I will do that. May take a few days as I do have some "real" work I'm supposed to be doing.

[Heuer]

A quick scan of eBay suggests there may be other candidates for a donor than the Pontiac Fiero. The Land Rover Defender, Rover 75 and various VW's could be likely candidates. Just needs someone to take the E-Type unit to a scrap dealer and rummage through the shelves. It looks like all the fans conform to a similar aero principle so maybe all that is required is a more powerful motor with SNG fan attached? Basically an easier option than the relatively rare Fiero unit and metal cutting. There must be something out there that is more plug 'n play.

[kingzetts]

First off, I agree that it would be great if a European substitute could be identified and I started off with that as my goal. Unfortunately my local scrapyard said "we hardly keep any parts on the shelf any more, we make all the money on the metal and there's no money in parts any more". I don't have any other scrapyards near me, and getting eBay vendors to provide detailed dimensions was very hit-and-miss.

The only way to avoid cutting the heater box is to stick with a 5" diameter or less fan - same as the original - because that's the size of the holes. If you want a bigger diameter you need to cut. If you won't cut, stick with the SNG fan. Removing the wire mesh on the top and fitting the fan onto the pre-installed motor doesn't help, by the way, as the hole in the top and the hole in the bottom are the same size.

I spent a LOT of time looking carefully at pictures of fans on eBay. A lot of the fans out there - actually most of them - rotate the "wrong" way for our needs and I was endlessly disappointed. I did try reverse polarity on a Peugeot fan which was the right cage size but wrong direction of rotation - the current draw was far less in "our" direction indicating much less air being moved. The only one I found which went the right way and was the right size was the Fiat Punto Mk 2, although there are probably others.

Then there's the method of mounting. The easy way is to have a flat metal plate like the original, which the Fiero does have, which can simply be bolted to the bottom of the heater box in the same way as the original. But, an awful lot of modern fans are in moulded plastic casings, which often have additional buttresses, inbuilt ducts, and other protruberances making the housing quite bulky. Now I could have made up brackets to attach the Punto motor housing, but it would have looked a lot less neat and tidy and (dare I say it) far less close to "original". The Peugeot housing was just as bad. I just couldn't track down a fan which was the right size, went the right way, had a flat metal base, and looked OK. I even thought briefly about fabricating a metal housing to hold the Fiat motor, but decided it was getting beyond a joke.

In the end I decided to try a Fiero fan. I also bought a fan off a Pontiac Sunfire or suchlike of a mid-80s vintage which has the same motor. This was $10 cheaper - unfortunately while the motor is the same, the fan cage is not and was much taller, but at least I have a spare motor.

My point here is that I don't think the Fiero fan is actually a rare item. First off, there were LOADS of Fieros sold in the US in the 1980s - like MX5s in the 1990s they were ridiculously popular. So there's a steady supply of them from breakers. Secondly, the motor (but not always the fan cage) is common to a LOT of other 1980's GM models as a cursory browse on eBay US will soon reveal. So used motors are not hard to come by, and both motors and fan cages are also available new at not-too-exorbitant prices. Of course this means buying from the US, which with Paypal and a UK eBay account is no harder than buying from the UK, and I've found typically it takes 2 weeks for stuff to arrive. I think I've even got the part numbers lying around somewhere.

The GM motor fits so well I am now convinced it was worth the slightly higher cost of getting one from the US. And before anyone asks, I did look at mounting the Punto fan cage to the GM motor - it doesn't fit.

So I reckon the Fiero is a good option - but if someone can identify a Euro fan which does as good a job, let us know and go for it.

[kingzetts]

By the way (I keep doing this - remembering stuff after posting) I did try mounting the standard fan on the shaft of the Punto motor - it moved a lot less air than the Punto fan. Air volume moved is a function of fan pumping capacity which will be a function of fan size, blade design and rotational speed. Power required will then be dictated by the air moved. So a more powerful motor on the standard or SNG fan will not move more air unless its rotational speed is higher. I tripped up on this - my first attempt was to fit a more powerful motor (the popular Clayton) to replace my knackered standard motor. The output was still (as memorably described by Skiday) like an asthmatic fly, probably because it was not actually turning much (if at all) faster.

I believe the maximum rotational speed of a given DC electric motor is achieved at zero load and is a function of the voltage applied to it, and the speed reduces under applied load. I presume, though, that different motors run at different no-load speeds on a given voltage, so I don't know if the Fiero, Punto or Peugeot motors run faster than the standard motor or not.

[Heuer]

Yes but would the SNG style fan work with the Fiero motor?

[kingzetts]

No, afraid not. The Fiero motor protrudes up inside the centre of its fan which is why although the motor is longer, it does not protrude out below the heater box any further than the standard fan. The SNG fan assuming it is the same shape as the original will not go down low enough on the Fiero shaft and will foul the underside of the heater box top panel or poke out through the hole for the mesh.