Size of radiator ducting

[C Lee Farquar]

My rad is rear mounted above the engine and I'm trying to change the air in ducting. The rad has twin fans mounted on a cowl. Would it be fair to assume I need a similar size duct to the size of the fans? The open area of fans totals about 85000 mm2 which makes for a bit bigger duct than I would like.

I could let it source some air from the engine bay but obviously that would be pretty hot being sat on the inlet above the headers.

[stevieturbo]

According to some books. Any duct inlet only needs to have about 1/4 of the frontal are of the core itself.

I guess it can make sense, given how much "solid" there actually is on the front of a radiator, where air cant actually pass through

[MattYorke]

That's what Corky Bell's book says.

[chuntington101]

stevieturbo said:

According to some books. Any duct inlet only needs to have about 1/4 of the frontal are of the core itself.

I guess it can make sense, given how much "solid" there actually is on the front of a radiator, where air cant actually pass through

Thats intresting Steve. I know there was a theory on WW2 radial engines that its actually better to have the incoming air slow right down as it passed over the hot cylinders. i guess the same thing here. can fans make up any for less than 1/4 frontal area?

[C Lee Farquar]

Thanks, I'll have a measure up and see how that looks. The fans are high output Spals. They suck twice as much air as their slimline ones, by their figures. They are heavy though.