The 1649A Constellation had a phase sync that worked similar to that on the L188 in that it synced the props so that they would position in a phase aray, thus minimizg the noise. The DC6B and DC7C has engine syncronizer that used either #s 2 0r 3 as the master. As I recall you pushed a sysnc button the the RPMs would move up to 4% to match the master engine. Don't bet any big money on that explanation!
