5717 Flex-a-lite 6 blade replacement for 3955182
I am very curious to know if anyone has contemplated or tried replacing the original 7 blade GM# 3955182 fan with a 6 blade replacement 5717 from Flex-a-Lite. The blade pitch is 32 degrees on the Flex-a-Lite 6 blade fan. With the prices of the originals on Ebay in the $400+ range, this makes this one a more reasonably priced replacement if it will flow enough CFM for the 70 LS5 with upgraded Vintage Air and Dewitts aluminum radiator. Has anyone used this fan and observed results? I am finishing up the restoration on my 70 LS5, so any help would be much appreciated.
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Re: 5717 Flex-a-lite 6 blade replacement for 3955182
Siegfried, Way back years ago before NCRS, in 1973 I was too inexperienced to know better, however I removed the original fan assembly from my 1968 Corvette 327/350. Living in Dallas and hot summer was looking for better engine cooling and tried the Flex fan. It made some air moving noise and I used it until late 70's. Removed it because one of the aluminum blades from the Flex fan separated and cut into lower radiator hose when my wife was returning home from a road trip in the 68. A service station attendant did a very good job using duct tape to seal the cut in the lower hose that provided for her remaining trip home.
Living on a military income I replaced the fan with one that worked from a Pontiac car from a salvage/junk yard and bought a new fan clutch. Still using it today. Not keeping original removed parts was a mistake due to storage space and not knowing the value of keeping the 68 original.
An original type 1968 327/350 fan would be expensive today. -
Re: 5717 Flex-a-lite 6 blade replacement for 3955182
If you are experiencing high operating temperatures, the easiest way to lower them is to optimize the spark advance map. The OE map was set up short and lazy to increase EGT in order to oxidize HC and CO, but this increases operating temperatures and places a very high load on the cooling system.
As specfied in the AMA specs (and also in your CSM) the maximum centrifugal is 22* @ 3200 which is both short and lazy. With the recommended initial timing of only 6* total WOT spark advance is only 28 versus the ideal range of 36-40, which is WAAAY short, so you're sacrificing across the range torque/power and fuel economy because so much energy is being thrown out the exhaust port and heating the coolant up along the way.
Get some light springs, then disassemble the distributor and grind the slot to allow 28-30 degrees centrifugal, which should all in at about the same RPM with lighter springs, and set the initial timing at about 8-10.
In the meantime, buy a 1/8" tee and a foot or two of 1/8" vacuum hose . Remove the existing hose from the carb base to the choke vacuum break and use the tee and new hose to fabricate a harness that connects the port on the carb base to both the choke vacuum break and VAC, and bump the initial up to about 14.
This may work so well than you may decide not to modify the distributor total centrifugal, but go ahead and try some lighter springs.
The OE VAC is 0 @ 7, 12 @ 12, so it's okay to use because it meets the Two-Inch Rule. If it needs to be replaced, get a B26.
There are HUGE benefits to be mined from optimizing the spark advance map as outlined in my 2012 San Diego National Convention presentation, especially on emission controlled engines with ported spark advance.Comment
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Re: 5717 Flex-a-lite 6 blade replacement for 3955182
The reason for fan replacement is that is accidentally fell off a shelf during the restoration. 3 of the 7 blades have been damaged, and I do not want to risk damaging the new water pump bearings due to an imbalance after straightening the blades. I would be interested if anyone may have an original, new or used for a reasonable price, date code not important.Comment
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