im an AUTO technician and this is not true. u are right in the fact that if u put the clamp around the coil wire that it will read the ACTUAL rpm times the number of cylinders but it will not increase the output of the coil. the only things that affects the output of the coil are number of secondary windings, secondary circuit resistance, dwell (amount of time current is flowing through the primary winding of the ign coil). the number of cylinders has NO affect on how much voltage ur coil puts out.