Governors on 345/392 engines...

[jmbrodsky@domain.elided]

     IH all,
     
        I posted about this some weeks back but never heard a reply.  
     The questions is:  How does the governor work to limit the revs at 
     3900 for the 345 and 3600 for the 392?  Is it electrical, and if 
     so, can I use it to power a tach drive?  If it's mechanical 
     how-d-hell do they do it?  It seems to really drop off quick in 
     power when I get around 3500rpm, but it doesn't sound like it's 
     cutting the ignition.
     
        Any ideas?  I'm just curious, and I'm not planning on going up 
     to 5000 rpm soon, like any Ch@^y owner out there.
     
        Thanks,
     

     -Joel Brodsky

         '76 IHC Scout II 345/tf727
         '75 IHC Travelall 150 4wd 392/tf727
         '72 Chev Carryall 3dr 4wd 350/th350 sold, but not forgotten.