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Converting a current driven tacho into an electronic tacho

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This is a small project i did last week to integrate the current driven stock tacho ("four wire tacho") of my '72 240Z with a new Megajolt ignition.


The conversion enables the tacho to accept standard square wave tacho signals from electronic ignitions such as Megajolt, Megasquirt, Bosch, MSD etc. After a quick calibration the tacho was surprisingly quite precise (less than 3% error), not bad for a 38 year old instrument. Cost of material is below $10, time to build the circuit and install is 2-3 hours.







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This post is amazing and I know that a number of people on the RB forum will be very interested to see this.


I am presently trying to adapt a a 280z tacho to work on a Nissan Rb26DETT engine fitted to my 240z. From your great write-up it seems that this would be a Kickback controlled tacho.




The RB engine uses a Coil on Plug (COP) ignition system. I am using an Apexi Power Controller ECU and this has an output for the tacho signal but will not drive the tacho directly.


Have you any advice as to how I might get this to work?


Thanks in anticipation

Edited by Bishopsrock

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It does look like a kickback controlled tacho. I have no experience with the 280Z tach, but the simplest approach probably would be to use a standard tacho adapter such as the MSD 8920 to convert the Apexi tach trigger to a compatible kickback ("voltage triggered") signal driving.

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