SharkSkin

I left it in there. It works like it's supposed to, and I saw no reason to change it. I know it's a bit redundant, but it helps the AC work when I'm first starting up on a hot day.

SharkSkin

The fan has an integral(albeit thin) shroud. In this case the only variable I have to work with is proximity to the radiator, and it's as close as it can go.

Fastest928

Thanks Mark, I just wish I could weld that well.

The fans are ducted, and raised off the radiator, similar to the factory originals. We also have another shroud setup ... but we only sell the shroud and fans separately so you can build your own setup. See DEVEK december Rennlist specials on this forum.

docmirror

Ah, the centrifugal air flow discussion! We could spend billions of electrons on this one. Ducted, vs non-ducted, radial air flow dynamics, etc. Lots of trade-offs. Do we want super high flow from a modest number of fins? Or, do we want less flow, from a larger cross section of fins? The age old question. This is one of the questions I mentioned before, with the testing comment. What field experience is there in the 928?

Some setups work better in a flush mount, some setups work better in a set-back arrangement. I just don't know with this radiator, with this frontal area, with this fan selection, duct work, etc. One thing I can say for certain. If you are going to use a duct at the edge of the blades, get it as close to the end of the blade as possible. The air will always try to find a path to the area of low pressure, which is in front of the spinning blades. The duct is supposed to prevent this, by forcing the air out the flat end of the blade, and back away from the axis of air montion. Too often I've seen ducts with gaps of 15mm or more. This sort of defeats the purpose of even having a duct around the blades.

In a situation where the air is already going very straight, i.e. thorugh the fins of the radiator, the flush mount generally is more efficient, simply because it moves more air in a straight line (axially). But, there are always exceptions. Fin spacing, and depth of the cooling path can both play a significant part in better overall flow with a setback design. A lot of modern cars use a setback design because it is cheaper than flush mounting to the radiator. In some cases it may also be more efficient. Really hard to say, without plenty of calorimitry tests.

Puller is almost always more efficient than pusher. Ducted(tightly) is almost always more efficient that non. Big blades, at slow speed is almost always more efficient than thin blades at higher speed. But, those big blades block free flow when not in motion, so a trade-off. Still want to see some afterburner pics on that big beef setup! whoooosssshhhhh!

sublimate

So I'm doing a little online research on fans (it's a Friday - work is light) and the first site I come across:
http://www.centuryperformance.com/coolingsys.asp
has this to say, "Never use both a pusher and puller electric fan on the same radiator." Not sure why or if it's accurate, but just thought I'd pass it along Mark.

SharkSkin

One risk is that if only one fan is energized, the other fan could turn into a generator, feeding power back into the system in undesirable ways. If they were both on the same circuit, I don't see how it could be a problem. You would not double your airflow this way, but it should improve somewhat.

rob rossitto

hey mark! neat product!

so should I dump my new "sale" shroud now cause it's obsolete, or use it for my stroker? if I keep it, which fans do you recommend? it's in an 85 chasiss w/89/gts motor stuff (TB, covers, etc), and your aluminim radiator (can see my sig for more specs if you need details)

ps your sig D-E-V-E-K dials a nice old lady that knows nothing about sharks or cars, but has a grandson in LA and she likes to cook... don't call her or she'll give you her life story too (LOL)... anyway, you might want to chg it to DEVK to get the right phone numbers for your shop....

regards!

WallyP

A bit if clarification on my fan shroud comment...

A puller fan will move more air if the blades are not buried in the shroud - that is, if the shroud ends near the front of the blade ends. This allows the blades to throw air out, as well as pushing it back.

If you have a non-shrouded fan, feel (cautiously!) around and behind the fan - you will normally find that there is a great deal of air coming off the ends of the blades, flowing almost straight out.

The same research showed that there were definite trade-offs in radiator construction.
-Too many very fine fins slowed the air too much, and gave less cooling. Too few too coarse fins had less surface area, and gave less cooling. If I remember correctly (it's been several years), 13 fins per inch was the most efficient level.
- The number of rows of tubes made a difference. Two rows worked better than one, three was some better, but four rows didn't work. The last row got little cooling, because the air was hot when it got to that last row, so it just acted as a bypass, flowing hot coolant around the radiator core.
- The air flow thru the radiator stalled and slowed, with the speed depending upon the number and spacing of fins. The 13-fin radiator gave an air speed of 13 mph (that made it easy to remember!) regardless of road speed. That also means that a shroud and fans aren't likely to block air flow, since the air can speed up going by them.
- There is amazingly little difference in the coolant temps in and out of the radiator at steady-state conditions (such as highway cruise). In fact, for their set-up, it was something like 195 in, 193 out. The only thing that really matters is the number of BTUs moved vs the number being generated. With high coolant flows, each ounce of coolant only has to move and give up a little heat.

As Doc says, we could waste a lot of time on this one...

Ketchmi

Ok, I weighed our fan system today. It came in at just under 12 lbs. with the adjustable thermostat, relays, circuit breaker and wiring harness.

Our fans are staggered, the inlet side fan (passenger side) is very close to the radiator fins and the driver's side is almost flush with the shroud. With the velocity these fans create, there is a massive amount of flow. I am not too worried about reversion or side slip since I can easily feel air movement from in front of the a/c condensor with the fans on. There are two methods of thought here, efficiency or overkill. We opted for overkill. The outer edge of the fan blades are less than 1/4" from the edge of the shroud.

As if stress testing during Open Road Racing wasn't enough, we even put my car in the paint booth on bake at 130 degrees to test this system. It still didn't overheat! Under normal conditions, the fans come on for a minute or two after exiting the highway and cycle on and off during town driving, usually never staying on longer than a couple of minutes at the most. If noise is a concern, a variable speed controller would be the ticket. We haven't had a chance to test one yet, been too busy with the X-over, driving lights for OB's, Twin Turbo brake systems, etc.

Fastest928

Dave,
Can you tell me what open road racing has to do with stress testing a fan design? We ran almost an entire race with NO FANS .... lost a belt and took out the wiring fan harness! Now if your tech speed were 30 mph, you might be on to somthing.

At the rate your advertising on this forum, I am sure we are all looking forward to you
becoming a Rennlist sponsor!

Ketchmi

I'm sure that you have had to sit in line waiting, and waiting, and waiting.......in driving suits and harnessed up. I had the a/c cranked to the teeth, front and rear, sitting absolutly still in the Nevada desert heat for up to an hour at a time. The Pony Express was especially bad with the delay for crickets, restarts, fires, wreck and rain. I was on the starting line and the count was down to 3 when it was shut down and restarted once. It didn't help that my navigator was even larger than me. A 928 gets pretty small inside during delay's.

It does prove good airflow capabilities past the fans when moving also..........

Believe me, as soon as I can convince John D. and Garrity to get together by phone or even by e-mail, we will be sponsors.

T_MaX

What Wally said! Prop wash is a bad thing