Is Nailhead tach ok on HEI distributor

[mdkd]

All

Can I use a mid 60's Buick tachometer off a Nailhead on the tachometer side of an HEI distributor?

Milton

[Loren At 65GS]

Milt,

   So, your question got me wondering.
 
 What I found is some mixed points of view. What stands out is that an analog tach , like what we have as an original Buick part, needs a constant signal. HEI does not put out a constant wave signal. That in turn allows the analog tach to read fine at idle, but when RPMs spike the tach will go up then drop to nothing and then recover slowly.
There is a solution for this. It is a tach filter that is wired in line between the distributor and the tach wire.
From what I read, Accell and Mallory have a filter.

  Loren

[mdkd]

Loren

Thanks for the heads up.

It looks like these run $25 to $100.

Milton

[Loren At 65GS]

Milt,
  Welcome

  Loren

[Fun401]

Milton, you could build a filter very easily and cheaply. $25-100 looks like a lot of money for about $5 worth of parts. It involves a 5.6k & 10k resistor, and a 0.1mf and 100pf capacitor.

 Here's how:

                                Tach terminal---- 5.6k ---- 0.1mf cap (+) to---- 10k ---- 100pf (+) ----- to tach

                                              the resistors are in series, the caps have one end in the circuit and the other will go to ground. In other words you'll have two leads from the caps that will need to be grounded, one "in" lead and one "out" lead.

 Get the stuff at radio shack, or ebay, for cheap. 1/2w resistors are fine and at least 25v caps. Mount it in a small "project box". Hope this makes sense.