Fans - push or pull?

[djc100]

Hi,
I have twin fans mounted in front of the rad, it looks like the fan & motor casings will push a lot of air away from the rad (when not running) - it seems more logical to put them behind pulling air thro' - what is the norm / best?

David

[thebirdman]

Hi David, PULL fans BEHIND the rad is the way to go to make the most of the cool air flow when the vehicle is moving.

[GreenV8S]

Some fans have symmetrical blades which will run either way, but the best ones are asymmetrical and only work well one way round. Sometimes the asymmetrical blades are reversible so you can run the fan either way but not always. So depending which fan you have you may find that it is only suitable to work as a puller or a pusher.

There isn't any fundamental performance benefit to pushing or pulling and packaging considerations are usually more important, but if you have a ducted radiator there are small benefits to putting the fan upstream of the rad so that it is pressurising the duct; this means that any leaks in the duct let cold air out rather than letting hot air in. Assuming the leaks are small the benefits are also small and hardly worth worrying about.

[thegamekeeper]

It depends which fans you use

[TVR_owner]

Adrian@ said:

thegamekeeper said:

It depends which fans you use

I forget that... most the twin fan setups I fit are to my shallow but deeper turbo radiators, and they are designed to take the 8 inch fans mounted directly onto the core on the pull through mounts...set in my ways and my customers won't buy into these motor cycle versions.
Adrian@

All purists that would not want there cars modified in any way then??

[rapidfrits]

I have 2 SPAL fans pulling on my 2500M. Can send pictures if you want.

[djc100]

rapidfrits said:

I have 2 SPAL fans pulling on my 2500M. Can send pictures if you want.

Yes pic please. I agree with Adrian (above) the twin 8" fans 'pushing' are a very neat set up and effective when running but I do believe they reduce effective 'airstream' cooling, However space does seem very limited behind the rad.
r's
David

[threespins]

Two motor bike fans fitted behind work a treat.

[ATE399J]

Having spent 15 years working as an aerodynamicist I'm pretty sure it makes very little difference whether fans are behind or in front (assuming they are being used as intended). What is more important is the distance between the fan and the radiator and / or the ducting. Making sure that the fan's energy is used in pushing / pulling air through the radiator and not wasted just recirculating it will improve efficiency.

Ducting from the air intake in the bonnet to the rad core will maximise "ram air" cooling. The other thing to remember is that the hot air has to escape from under the bonnet somehow, while moving this shouldn't be a problem but while static heat will rise and needs to get out so don't block bonnet vents!