Engine fan help

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TIB3300
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Engine fan help

Post by TIB3300 »

Morning :thumbright:

Just looking at other options for a manual engine fan, I currently have a 17in 4 blade fan pictured , But would like to reduce the size to a 15in fan?

I've been looking at these five blade fans..

My question is really, If I go for newer a 6 blade fan15in. Will it be as efficient as an old type 4 blade larger fan ?

https://www.speedwaymotors.com/Flex-A-L ... 29388.html
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Blue
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Re: Engine fan help

Post by Blue »

It seems logical to assume more blades will move more air, you have possibly gained back the surface area than you've lost by reducing the diameter. Combined with a shroud it will probably work out. I would't normally suggest it but given your lack of space, have you considered an electric fan from a late model American V8 car? How wide a radiator core have you got space for?
"Jesus died for somebody's sins but not mine"

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Dave999
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Re: Engine fan help

Post by Dave999 »

you tend to get issues with cooling when the motor the cooing system was designed for, changes its RPM range dramatically with no change to the gearing of the pulley system for the pump/fan

a pump, pumps best in a pre defined range of rpm and a fan sucks best when matched
capacity of the radiator, the number of passes through the radiator, the thermostat temperature setting, and the rpm range of pump and fan are matched so the car can trundle about in slow traffic in California summer heat i.e at 1000 -2000 rpm the water pump is coming on song and it will be pumping its maximum in the 4000-5000 rpm it will tail off with higher RPM. so for say a car that was set up for racing... cooling system gearing should be changed to slow the pump down and make it run at the rpm it would see at 4000 engine rpm on a standard motor i.e when the engine is running at say 7K rpm the pump thinks the engine is running at 4k. that way pump runs at max efficiency when the engine is doing its hardest work.
i don;t think you need to worry about that stuff here.

the radiator spec and grill are specified to allow the car to operate at high RPM and high speed in California summer heat but at that speed the fan is just an hindrance disrupting smooth flow and robbing HP... thats why viscous coupled fans are popular. they practically free wheel once the rpm is up to a specific level so they don't rob HP.

Other option would be a plastic flex fan. the vanes pull air at low rpm but rotation at High Rpm flattens them so they do very little.. worth looking at...

as your motor will still be designed to run most of the time at street RPM and won't be idling at much more than 100-200 more rpm than the system was designed for id suggest it will stay cool enough when idling and once you get up to about 30 MPH the cooling really has little to do with fan speed its more to do with air speed and the pump working efficiently.
as the gearing of the pump will still match the rpm range it was designed for and the motor will still operate in more or less that range provided the radiator is up to capacity the fan will have little effect on normal running and will hopefully still be perfectly good for idling in traffic.

basically the only motor i ever changed the gearing on for cooling was an air cooled vw flat 4 in a beetle with a none vented bootlid higher CR and a cam/intake combo that liked to idle at 1200 rpm. fan on these steals about 30% of the available power and they have a habit of exploding (pressed together) so having it run slower gave some of that back and reduced the risk of shrapnel
David Gray. This year i am mainly In Twickenham, sometimes in Watford, often between the two but only between the hours of 07:00 -09:00 and 17:30-19:00

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TIB3300
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Re: Engine fan help

Post by TIB3300 »

Blue wrote:
Tue Feb 23, 21 8:47 am
It seems logical to assume more blades will move more air, you have possibly gained back the surface area than you've lost by reducing the diameter. Combined with a shroud it will probably work out. I would't normally suggest it but given your lack of space, have you considered an electric fan from a late model American V8 car? How wide a radiator core have you got space for?
"considered an electric fan"
Yes but not at this point, I want to keep things simple and once the car is up and running change things :thumbright:
"How wide a radiator"
Its not the rad core size it's the metalwork either side I have to keep within.The 17 fan is OK for side to side it just too close to the top for my liking 8-[

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TIB3300
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Location: Sheffield

Re: Engine fan help

Post by TIB3300 »

Dave999 wrote:
Tue Feb 23, 21 10:32 am
you tend to get issues with cooling when the motor the cooing system was designed for, changes its RPM range dramatically with no change to the gearing of the pulley system for the pump/fan

a pump, pumps best in a pre defined range of rpm and a fan sucks best when matched
capacity of the radiator, the number of passes through the radiator, the thermostat temperature setting, and the rpm range of pump and fan are matched so the car can trundle about in slow traffic in California summer heat i.e at 1000 -2000 rpm the water pump is coming on song and it will be pumping its maximum in the 4000-5000 rpm it will tail off with higher RPM. so for say a car that was set up for racing... cooling system gearing should be changed to slow the pump down and make it run at the rpm it would see at 4000 engine rpm on a standard motor i.e when the engine is running at say 7K rpm the pump thinks the engine is running at 4k. that way pump runs at max efficiency when the engine is doing its hardest work.
i don;t think you need to worry about that stuff here.

the radiator spec and grill are specified to allow the car to operate at high RPM and high speed in California summer heat but at that speed the fan is just an hindrance disrupting smooth flow and robbing HP... thats why viscous coupled fans are popular. they practically free wheel once the rpm is up to a specific level so they don't rob HP.

Other option would be a plastic flex fan. the vanes pull air at low rpm but rotation at High Rpm flattens them so they do very little.. worth looking at...

as your motor will still be designed to run most of the time at street RPM and won't be idling at much more than 100-200 more rpm than the system was designed for id suggest it will stay cool enough when idling and once you get up to about 30 MPH the cooling really has little to do with fan speed its more to do with air speed and the pump working efficiently.
as the gearing of the pump will still match the rpm range it was designed for and the motor will still operate in more or less that range provided the radiator is up to capacity the fan will have little effect on normal running and will hopefully still be perfectly good for idling in traffic.

basically the only motor i ever changed the gearing on for cooling was an air cooled vw flat 4 in a beetle with a none vented bootlid higher CR and a cam/intake combo that liked to idle at 1200 rpm. fan on these steals about 30% of the available power and they have a habit of exploding (pressed together) so having it run slower gave some of that back and reduced the risk of shrapnel

Do you think I should I buy one Dave ? :lol:

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