Any Scientific Tests on Electric Radiator Fan savings ??
07-10-2004, 12:38 PM
#1
Racer
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Any Scientific Tests on Electric Radiator Fan savings ??
Ive heard and read savings in h.p. of up to 20 . Just wondering if anyone has ever come across actual proven test results ??
I have twin electric radiator fans and they only come on if im sitting in traffic ; once im going at least 35 mph and the outside temp is not hotter than 85 f., they do not come on. (they are set to come on at 205 f and off at 190 f). I take very good care of my cooling system, plus, it has a larger radiator,Stewart 6 impeller hiflow water pump, and no a/c ... which might have something to do with it.
Thanks, Dave
I have twin electric radiator fans and they only come on if im sitting in traffic ; once im going at least 35 mph and the outside temp is not hotter than 85 f., they do not come on. (they are set to come on at 205 f and off at 190 f). I take very good care of my cooling system, plus, it has a larger radiator,Stewart 6 impeller hiflow water pump, and no a/c ... which might have something to do with it.
Thanks, Dave
07-10-2004, 12:56 PM
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Melting Slicks
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No "scientific" that I know of, just a magazine article I read. There was a great amount of savings from a fixed fan to an electric. Less savings from a flex fan, but still a good amount. Minimal savings from a clutch fan in perfect operating condition. The electric is lighter and the pull is greater at idle so it's easier to sit in traffic with an engine that's not too keen on idling.
07-10-2004, 05:17 PM
#3
Melting Slicks
I ran my car on the dyno with and without a clutch fan. I picked up 15hp and 12ft-lbs of torque without the fan and clutch. I have since switched to an electric fan.
07-10-2004, 06:11 PM
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Drifting
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I have a book which gives a graph of accessory losses vs. rpm (Internal Combustion Engine Fundamentals by Heywood) in a 5.7L V8. It quotes two SAE papers which I can give you references for if you like. I haven't looked them up myself.
The result is that the power required to drive a solidly mounted fan increases with rpm cubed! In this particular example, its about 3.3 hp at 3000 rpm and 16 hp at 5000 rpm. A viscous fan drive required about 3.3 hp at 3000 rpm and 6.7 hp at 5000 rpm.
There's no listing for an electric fan, but its easy to estimate. I'll guess a big one takes 20 amps, which implies 0.3 hp. Then the alternator isn't very efficient, so maybe double that to 0.6 hp. This is less efficient than a mechanical fan at idle (the only place you need it), but the mechanical couplings don't disengage very well, so you'll read a few hp imrovement at higher revs where everyone reads off their peak power. Maybe modern fan clutches work better? This data is from the same era as our cars.
Another issue with mechanical fans is rotational inertia, which can get pretty bad if the clutch doesn't let go early. This cannot lumped together into a general power loss. Unfortunately, most dynos do not accurately measure power, so they're taking this into account also (in a way that isn't meaningful at all), which will give you more "improvement."
The result is that the power required to drive a solidly mounted fan increases with rpm cubed! In this particular example, its about 3.3 hp at 3000 rpm and 16 hp at 5000 rpm. A viscous fan drive required about 3.3 hp at 3000 rpm and 6.7 hp at 5000 rpm.
There's no listing for an electric fan, but its easy to estimate. I'll guess a big one takes 20 amps, which implies 0.3 hp. Then the alternator isn't very efficient, so maybe double that to 0.6 hp. This is less efficient than a mechanical fan at idle (the only place you need it), but the mechanical couplings don't disengage very well, so you'll read a few hp imrovement at higher revs where everyone reads off their peak power. Maybe modern fan clutches work better? This data is from the same era as our cars.
Another issue with mechanical fans is rotational inertia, which can get pretty bad if the clutch doesn't let go early. This cannot lumped together into a general power loss. Unfortunately, most dynos do not accurately measure power, so they're taking this into account also (in a way that isn't meaningful at all), which will give you more "improvement."
07-10-2004, 06:42 PM
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Racer
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Originally Posted by aharte
I have a book which gives a graph of accessory losses vs. rpm (Internal Combustion Engine Fundamentals by Heywood) in a 5.7L V8. It quotes two SAE papers which I can give you references for if you like. I haven't looked them up myself.
The result is that the power required to drive a solidly mounted fan increases with rpm cubed! In this particular example, its about 3.3 hp at 3000 rpm and 16 hp at 5000 rpm. A viscous fan drive required about 3.3 hp at 3000 rpm and 6.7 hp at 5000 rpm.
There's no listing for an electric fan, but its easy to estimate. I'll guess a big one takes 20 amps, which implies 0.3 hp. Then the alternator isn't very efficient, so maybe double that to 0.6 hp. This is less efficient than a mechanical fan at idle (the only place you need it), but the mechanical couplings don't disengage very well, so you'll read a few hp imrovement at higher revs where everyone reads off their peak power. Maybe modern fan clutches work better? This data is from the same era as our cars.
Another issue with mechanical fans is rotational inertia, which can get pretty bad if the clutch doesn't let go early. This cannot lumped together into a general power loss. Unfortunately, most dynos do not accurately measure power, so they're taking this into account also (in a way that isn't meaningful at all), which will give you more "improvement."
The result is that the power required to drive a solidly mounted fan increases with rpm cubed! In this particular example, its about 3.3 hp at 3000 rpm and 16 hp at 5000 rpm. A viscous fan drive required about 3.3 hp at 3000 rpm and 6.7 hp at 5000 rpm.
There's no listing for an electric fan, but its easy to estimate. I'll guess a big one takes 20 amps, which implies 0.3 hp. Then the alternator isn't very efficient, so maybe double that to 0.6 hp. This is less efficient than a mechanical fan at idle (the only place you need it), but the mechanical couplings don't disengage very well, so you'll read a few hp imrovement at higher revs where everyone reads off their peak power. Maybe modern fan clutches work better? This data is from the same era as our cars.
Another issue with mechanical fans is rotational inertia, which can get pretty bad if the clutch doesn't let go early. This cannot lumped together into a general power loss. Unfortunately, most dynos do not accurately measure power, so they're taking this into account also (in a way that isn't meaningful at all), which will give you more "improvement."
'There's no listing for an electric fan, but its easy to estimate. I'll guess a big one takes 20 amps, which implies 0.3 hp. Then the alternator isn't very efficient, so maybe double that to 0.6 hp. This is less efficient than a mechanical fan at idle (the only place you need it),
ME: I have twin electric fans out of a 1990's LT1 Vette in my 1970 BB Vette ; I tried fusing them at 25 amps (together) but it blew, but theyre ok on a 30 amp fuse. Mine seldom come on when im moving 35 mph or more...unless its 85 f or above ; so...without them running , i should be picking up some healthy h.p/tq versus a (1970 stock) mechanical fan thats always running.