Photo Tach

[Lin]

Since installing my alternator-driven tach, I have been needing to calibrate it more accurately.  I just checked Ebay and found that they have photo tachs for under $20. including shipping.  I figured, even though I will not use it much, any shop would charge me at least that much to turn theirs on.  Just passing the info on for anyone that might need one.

[Sammy]

I bought mine from the same place. Works just fine.

[RTS/Daytona]

For those that install alternator driven tachs - here's a little tip

For MOST Detroit Diesel Delco gear driven 50DN  alternators

The  R" Terminal output is 12 volt and (2.94 (53/18) gears & 6 pulses per revolution)

which equals  --->  17.66 pulses/rev)

so- if your tach came with a 12 pulse / revolution setting

         To re-calibrate for 17.66 pulses/rev - first start the engine & record the default
         12 p/rev RPM reading at a steady idle- then turn the adjustment device
         until the tach registers approx 2/3 or (12 / 17.66) of the original (12 p/rev) RPM
         reading

[Lin]

The tach came calibrated according to the info I gave the vender, but I am not sure of it.  It is adjustable while in operation, so I will use the photo tach to clock my no-load max and set the dash tach to it.  I figure that will get me as close as I can get.  It makes sense that the lower speeds should then automatically be right on, but what's life without surprises.