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There is a little difference in how much air they move, but not much. Thewre is, however great difference in at what speed they do things. The 5 blade fan originally came from a Carrera engine and was deigned to spin fast. When Porsche made the newer model engine they then developed the 11 blade fan and lowered the ratio from about 1,7 - 1 down to 1,4, and 1,2 - 1 depending on which engine you look at . The 5 blade has a "cool whining" to it if you like that. no one with a little gas in their blood will be in doubt of what is in there if you rev it. Where as the 11 blade is a little more "silent"
As for overcooling, well you have to do a little trial and error testing to find the perfect compination on your setup. But start with a known factor and work your way out from there.
With a 5 blade on a not too fast reving T4, I would say that 1,6 - 1 would be a good place to start.
Martin, Did you get my mail ?
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