johnt365

With an electric fan, does air need to blow over the engine? can it just pull through the radiotor? or do you need both.

i want to convert to a elec fan w/shroud but not the stock shroud. the angle of the radiator will not blow air over the motor. does that matter?

C3 Stroker

Your electric fan w/shroud should adaquately cool your engine....the cooled anti-freeze/water circulates through the engine to cool it....there is no significant airflow over the engine from the fan to cool it. (Even with the stock fan).

johnt365

So it sounds like you are saing that the air that blows over the motor is just a biproduct of pulling it through the radiotor.

WayneLBurnham

On all water cooled designs - the whole purpose of the fan is to pull air through the radiator, especially at low speed. With manual fans on vettes, the key thing is a shroud that totally encloses the radiator air tight in the back and comes as close to the edges of the fan blades as possible to generate as much suction as possible - since the fan is so far from the radiator, especially at the bottom.

With electric fans, the shrouding behind the radiator is largely irrelevant in most cases and the key thing is to get it as close to the radiator as possible. (Some systems, especially large single fans which cover a smaller percentage of the radiator surface with fans, pullers or pushers (less common on vettes), also take the radiator encasing appraoch used with manual fans.) You really want the fan sealed up against the radiator to not lose fan pull around the edges.

I am leary of a full shroud on electric fans in case it should restrict incoming air flow from being able to freely go through the radiator. Many high end setups do use this though. Mine (and others) do away completely with the radiator shroud with electric fan use. I took a long time making an elaborate skeletonized and double gasketted aluminum frame to mount my fans to and get them sealed against the radiator but with no restriction outside of where the edges of the fans are - and without any nylon things going through the radiator fins.

Important to both, especially with vettes, is air ducting from the bottom front to the radiator, regardless of fan arrangements. I did an armchair calculation with my three Zirgos (a 16, 9 and 8") pulling a combined 6500cfm only were equivalent to something like 12 mph on a radiator with the surface area of the vette if it was flat to the wind like a van. Clearly, even with huge fan flows, the important thing is incoming air from the nose and that none is lost going around the radiator either over the top or to the sides.

A number of respected people maintain electric fans can even interfere with "natural" air flow through the radiator at high way speed and should be thermostatically controlled or turned off. I have problems believing that - the fan blades are there whether or not they are rotating from the motor or not. This may be more of a problem with pusher fans in front of radiators, but I just don't quite see it with pullers - especially since they will speed up with wind going into them.

johnt365

thank you for the input. i still have some home work to do...

jbs75

I think it is required that air flow over the engine. This gets rid of high exhaust manifold heat primarily; but there are other sources as well. If you didn't force the air away from the firewall, it would pool there, and contribute significantly to cabin heat. Also the engine would be trying to breathe that very hot air. I can't say for sure if GM in there infinite wisdom would have made the air blow over the engine; but I suspect they would. After reading some comments about those "tunnels?" on each side of the fire wall; I suspect they are involved also. If I ever do a body off job, I'm sure goig to check those joints!

Jim

SanDiegoPaul

I tried w/out one and had no joy. I had a single Zirgo rated at 3600 CFM and figured it would work but I still ran hot. I put together a shroud for it but it was inadequate. I eventually got the dual spal setup with a proper shroud and now it runs 35* cooler than with the OEM setup.

Ganey

No, the purpose of the shroud is to better utilize all the rad. area.
It would not necessarily need to. Heat is bad for hoses, wiring, etc.
Do you have headers?
I could not care less about stock, however just because something is stock does not make it bad. Typically a lot of time & money is put into making it. Why do want to redo the shroud?

Ganey

While not something that guys who don't drive fast need to be concerned about...
True at high speed, both the shroud & fan(s) can interfere w/ flow.

johnt365

i do have regular headers and that warms up the under hood temps. i am currently running with no shroud and mech fan with no major cooling probs. my orig shroud was removed and broken by the previous owner.

i am thinking i should try to repair the original shroud and use a perma cool 14" elec fan. they look less restrictive and provide high rpm at low amps.

it sounds like an electric fan with a factory "like" shroud would be best. i may try to fab a shroud out of sheet metal

Gordonm

I just converted to a single electric fan with no shroud. It runs nice and cool. I have a stock LT1 radiator with a single 2400 cfm fan.

WayneLBurnham

which is why I did not go with one, and have all areas of the radiator not covered by the three fans open. I do not buy that a fan behind the radiator not spinning at all (or spinning at only the rpm induced from air going past it) will slow air flow down less than the same fan being powered to flow in the same direction.

I'm not sure, but I don't think normal electric fan motors have any governor on them - they go as fast as the amount of electrical power going through them overcoming the blades resistance to spin allows - if they are turning with induced flow from the front they will just go faster. I wonder what would happen to one in a vacuum or near vacuum? Would it speed up and speed up until the bearings (or something else) melted (especially since there would be no air flow to cool it) or something else broke apart?

If anything, I would think a clutchless mechanical fan which cannot speed up with impacted air like an electric can would cause more resistance at some particular air speed. Furthermore, I would think a clutched mechanical fan which freewheels or slips after a certain speed and/or temperature would offer more resistance to that freewheeling due to the considerable resistance of the clutch, the much larger mass of the blades (compared to electric fans), and the larger, more aggressive blade designs typical in lower rpm mechanical fans (again, compared to the thinner, faster spinning blades of electric fan designs.)

Remember, a jet engine is just a series of fans stacked one after another - each one increases the speed and pressure of the air going through it. Those rearmost fans are certainly at first trying to turn slower than the air flow going through them from the previous fans would let them. Each fan in the series increases the pressure and air speed from incoming to outgoing - I would think electric fans do exactly the same thing.

WayneLBurnham

important as gross flows. Although at nearly the last minute I found the new Zirgo 16" flowing 3950, I was debating another make that was an 18" (which BARELY can fit with a little overlap you can seal at the top and bottom) which flowed I think 3750. But I felt the area of the radiator covered by the fan suction was important also and a multi fan approach was better. Then I started totalling designs, sizes and total air flows and came up with the 16, 9 & 8. I was going to use the 16" Zirgo, the SPAL for one of the others and another make for the other when I found a bargain on the smaller ones, so I ended up all Zirgo.

Some interesting armchair calculations I just did, now, super-usefully, AFTER I spent $1300+ and 40+ hours making a fan support, gasket, wiring harness, modified Moroso switch panel and removing the old and installing the new:

Vette rad fin area nom. 18x26" +/- 1/2in ea = 460 sqin or 3.2 sqft
Z8.........500 cfm..50 sqin.0.35 sqft.1428 fpm.16 mph.11% cov.1.8 mph
Z9........1000 cfm..64 sqin.0.44 sqft.2273 fpm.26 mph.14% cov.3.6 mph
Z16......3950 cfm.201 sqin.1.40 sqft.2821 fpm.32 mph.43% cov.14 mph
S2x11...4400 cfm.190 sqin.1.32 sqft.3333 fpm.38 mph.42% cov.16 mph
16+9+8.6450 cfm.315 sqin.2.19 sqft.2945 fpm.33 mph.68% cov.22 mph

All errors are the fault of someone else, not me, no, never!

Tumarr

One other forum member steered me towards going to the junkyard to find a good fan for real cheap. What I came up with was a 94 lincon continental fan. Its a single with a 17 1/2 inch fan and powered by a big seimens motor. It also has a plastic shroud integrated into it that will cover 85% of the corvette radiator. I put it on my vette and eliminted the mech fan. Works great so far and is not too loud either. my thermostatic switch keeps it on only when its needed also. the fan and the painless wiring kit costed me a total of about 95 bucks.

Frankenvette

I've been running a 16" electric fan for about 4 years. I do not use a shroud and have had no problems with cooling the engine. I did get the fan mounted a close as possible to the radiator without actually touching it. I think it is also important to make sure all other parts of the cooling system are working properly. I love not having the pain in the a$$ factory shroud in the way when working in the engine bay. Also, I dynoed the engine with and without the mechanical clutch/fan. Picked up about 15hp and 12ft-lbs torque without the mechanical clutch/fan, so the electrical fan turned out to be a cheap gain in power.

Ganey

John

Did you know that an electric fan was installed on some C3s from the factory?
It was an aux. el. fan mounted to the shroud in front of the mech. fan.

PS Expect you probably don't have (working) A/C.

Ganey

Wayne

Yes, agree w/ you that an electric fan that is off at speed is fine.

Chuck Harmon

I did not use ANY shroud with my Spal fans on my L88. They kept everything nice and cool while driving in stop and go traffic when it was over 100 degrees outside. As Wayne B. put so well, the theoretical speed that fans pull air through the radiator is meager at best. An engine lazily turning at 2500-3000 rpm on the highway is blocking air with the stock fan, not helping the cause. As I have posted a few times before, a fan or propeller turning more slowly than the air that is trying to flow through it makes for a big Brake. This is how a prop pilot slows himself down when making an approach.

Shrouding is only for slow vehicle speeds. Speeds probably slower than you think.

Chuck

R. Bruno

So, you are running the spals with the shroud and no other foam seals?
I have the spals and an aluminum universal Griffin and still run hot on the highway with A/C on hot days on a stock motor adjusted to pass smog. I am trying to figure out why.

Brettmc

Check your chin spoiler. It needs to be pretty firm. If it's flimsy, it'll just flap around and not direct air up into the radiator.

Brett