Chris.....the flex fans of yesteryear were poor performers at moving air AND had a perpensidy to throw blades off due to the poor mechanical design. Usually the blades were attached with just a few cheap rivots (soft) and when the rivots got some miles on them they hollowed out their mounting holes (sometimes the blades were made of aluminum...another no-no because of the soft materials) and then castrophically failed when the mechanical action of the force of the blades actually cut the rivot...and off came the blade. The blades also gave it up due to metal fatigue of the loading point and usually cracked, then departed the scene. I have seen pictures of blades sticking thru hoods, not good to say the least. Another point, the hubs were made of inferior materials too allowing for poor attachment bases.
The combination of low airflow performance, mechanical design or the lack thereof, makes the old flex fans a good canoe anchor. I used to NEVER consider a flex fan. But times are changing and even OEMs are considering this newer technology.
The newer technology that uses a much higher grade of stainless steel typically used in aircraft applications can be bent to produce more air at slow engine speeds, yet will not metal fatigue like the poorer grade blades. In essence, the blades really load up at idle, and because they can be designed to flatten more at higher speeds. The attachment methods are much better with the "entrapment" design which not only holds the blades in place with high grade rivots, but utilises a companion plate which also supports alot of the entire leading edge of the blade to put more force on the blade to hold it on, disperse the force of the attachment compression and reduce the metal fatigue issue to nil. Just a better design all over. The hub materials are as good as or better than OEM style fixed bladed fans.
I researched this subject a few years ago when I was building my 69 and ran across a Derale fan engineer at the SEMA show in LVegas. I was studying the new line of Derale flex fans they claimed to be far superior and started with my usual dribble and soap box speech about flex fans. He agreed with my past analysis and assured me of the new line performance with all kinds of empiricle proof, including some pretty hefty cycling hours and rpms. He offered me one for free (since we were both engineers and in the business) as long as I would write a report to him at the end of two years which is coming up in the fall. The model that I am using is this one
Initially we put in on a racing engine on a dyno that turns in excess of 8800 rpms to give it a welcoming test and make sure that everything was what they said it was. Derale claims to guaranty these things to 10000 rpms even tho the data on testing goes to over 20000! I have already used it for going on two summers and just recently pulled if off to Xray for cracks at my favorite aircraft facility (I do airplanes too). I have found absolutely no material degradation and back on it went. The amazing thing about this fan is that it will cool my Camaro with the air a blowin' and I still can't hear the thing at 6500rpms? This tells me that the fan is really efficient.
Anyway Chris, I would recommend it now for certain applications and certainly for your 67. I am going to write an article in the Northern/Southern Rodder magazine coming before the end of the year after the full testing period is up.
Chris....if ya want the 69 you will have to see the wifey....it's her ride and now she has been driving it by herself to cruises etc.
Michael67....your radiator guy is right about the air condensing coil. The coil acts as an air block in that air rolling off the coil in front of the radiator will eddy current in the void space setting up unproductive flow and degradate the airflow pattern. Keeping the coil up against the radiator is the trick to keeping airflow moving smoothly and productively thru the system. I would look to change that situation immediately.
That's my story and I'm stickin' to it!
ConceptOne Pulleys and Brackets
Techical forum/links at www.inccn.net/techforum.htm
[This message has been edited by HOTRODSRJ (edited 06-18-2002).]