88 Especial

Hello, New to the forum, first post. For what it is worth, I installed a tachometer from a Kenworth tractor in my SIII diesel several years ago. I added a wire from a stator winding output, where it connected to the diode pack/rectifier. Counted the number of poles on the rotor. I have a Delco-Remy alternator and it has 14 poles. I believe the Lucas has 12. Measured the diameter of the alternator and crankshaft pulleys. Don't remember the sizes, but it was 2 +/- revolutions of the alternator for each revolution of the crank. My multimeter has a frequency function, used this to measure the signal from the alternator. I used the formula: f=p/2 X r/60. Where: f is the signal frequency in cycles per second, p is the number of poles, and r is the speed of the rotor in revolutions per minute. Knowing the frequency and number of poles, manipulate the formula to get the rotor speed. r=120 x f/p. The tachometer had a number of dip switches, adjusted these till the reading on the tachometer was as close as possible to the calculated speed. I lost most of my data in a hard drive failure, the attached spreadsheet has some data..Calculated speed.xls This was almost 10 years ago, so I may have forgotten something. Also I am retired so this project was something to pass the time. Cheers from Central America!