[willy]

Hi, i am a first time user to your site.
I have recently fitted a working hood tacho
only to find it came off a 6 cyl firebird
sprint. Can I make it read correctly fitted
on my 8 cyl 400 ?
It is an old original tacho not a repro. Any
help would be appreciated.

[willy]

Hi, i am a first time user to your site.
I have recently fitted a working hood tacho
only to find it came off a 6 cyl firebird
sprint. Can I make it read correctly fitted
on my 8 cyl 400 ?
It is an old original tacho not a repro. Any
help would be appreciated.

[cuz68]

Will work the same way on 6cyl or v8.

[Jack Blum]

Actually it won’t work . These old tach’s use the points wire to pull the tach signal to ground giving the tach 1 pulse each time the points close. The pulses keep a RC (Resistance/Capacitance) circuit charged, the frequency at which the pulses come in increase the charge on the RC circuit. Think of the RC circuit as a funnel, the faster you pour in water; the higher the level in the funnel goes up. The charge is then used to set the meter, or the dial you see. So the tach is expecting 6 pulses per revolution of the distributor, and if you hook it to a V8, it is now getting 8 pulses per rev. Thus it is probably reading to high. You may be able to modify the circuit boards RC components if you can get the internal schematic for a V8 tach. I remember seeing on this board a post for a web site that has the schematic.



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