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Suck or Blow (What's Your Preference?)
scootz - 1/8/08 at 04:24 PM

Still trying to work out the placement of my twin rads. The best place I can think of means I can only use sucking fans.

Now - I can understand how a fan can blow air, and I understand that it's pulling the air from the other side, but surely the blowing force is greater than the sucking force???

Ow - my head hurts!

worX - 1/8/08 at 04:28 PM

I prefer for air to be sucked through the rad...
(yes I thought long and hard [pff] on how to phrase that!)

Steve

philw - 1/8/08 at 04:29 PM

Will the air not blow through the rad?

My fan sucks by the way, and is adequate

indykid - 1/8/08 at 04:35 PM

if a fan blows, it does it by sucking the air from in front of the fan.

it's purely where the fan sits.

if you can't get your head round that, think of it as a fan making a lower pressure in front of it and the atmosphere pushing air in to fill the space. to fill the space the air has to flow through the radiator.

tom

sucksqueezebangblow - 1/8/08 at 04:36 PM

Think of it as the fan moving a volume of air. The same volume of air that goes in one side comes out of the other. Suck or blow, pretty much the same volume goes through the rad. Base your decision on where you have space to position the fan, and the natural direction of flow (i.e. you don't want the fan behind a front grille mounted rad blowing as it will be blowing against the force of air coming in through the grille due to the forward motion of the car. You would want it to suck so it is assisted by the natural air flow.)

designer - 1/8/08 at 04:53 PM

Sucking is more efficient.

jollygreengiant - 1/8/08 at 05:10 PM

Think of it like this, is it easier to pull a piece of string or push the same piece of string.

Alez - 1/8/08 at 05:12 PM

quote:
Originally posted by designer
Sucking is more efficient.


So Pacet say, so it must be true. They recommend to go for suck unless space restrictions don't allow to. Also most modern tin-tops use suck.

[Edited on 1/8/08 by Alez]

Agriv8 - 1/8/08 at 05:15 PM

Sorry but,

Quote Ben Elton ..... all I know is your not supposed to blow ......

....yes well my ears are bleeding ...

Suck in my book and its not the size its the CFM ( thats what I tells the wife anyhow )

Regards

Agriv8

matt_claydon - 1/8/08 at 05:24 PM

As far as fan efficiency is concerned it'll make bugger all difference as you'll have the same volume flow rate of air going through the rad. However, a blow set-up will compromise air-flow more than a suck arrangement during normal driving so suck is preffered where space permits.

chrisj - 1/8/08 at 05:34 PM

After experimenting a lot with suckers and blowers a race engineer confirmed that you should get the highest cfm fan/s you can afford and set them to suck over the largest area. However powerful the motor over a certain mph the fan (even when turned on) will come to a stop and possibly reverse direction. However, plausable/non plausable that may be your shrouding the front of the rad from free flowing cold air while your moving and sucking cold air when your in traffic. The next conundrum is getting rid of the unwanted hot air from around the block either by ducting it out over the bonnet or grilling the top of the nose/bonnet. Metro bonnet vents are quite reasonable, but i'm playing with some BMW 3 series kidney shaped rad grills to sit in the nose to increase the stationary venting.

bob - 1/8/08 at 06:18 PM

quote:
Originally posted by matt_claydon
As far as fan efficiency is concerned it'll make bugger all difference as you'll have the same volume flow rate of air going through the rad. However, a blow set-up will compromise air-flow more than a suck arrangement during normal driving so suck is preffered where space permits.



Before swapping the pinto for the zetec i did a test on the suck blow theme, deffinatly a restriction to air flow with the fan on the front of the rad and blowing.Its hard to read exact temps on the racetech gauge but i did notice a reduction in running temp, as for pulling or pushing when stationary i doubt their is any difference.

MikeRJ - 1/8/08 at 06:30 PM

quote:
Originally posted by jollygreengiant
Think of it like this, is it easier to pull a piece of string or push the same piece of string.


That's because a piece of string is strong in tension. Air can be compressed or expanded quite easily, so not really equivalent.

The radiator is a restriction whether it's behind or in front of the fan so airflow is not going to differ much in either case. The radiator mounting location is generaly determined by space constraints rather than any small performance differences from mounting location.

LBMEFM - 1/8/08 at 09:08 PM

Sucking is good.............

D Beddows - 1/8/08 at 10:55 PM

Your cooling system seems to be becoming a Friday night regular for me but if you're fitting a fan it needs to be behind the radiator which means it obviously has to be a sucking one. If it's on the front it'll muck up the airflow through the radiator at all speeds apart from 'stuck in traffic jam' so you'll just need a bigger radiator. The other option is to fit a fan on the front of the radiator, have it set to run all the time and cunningly duct all the air to it from an area on the front of the car that wont muck up the aerodynamics.....which is actually an interesting thought if you don't mind loosing the power required to run the fan!