Rev counter misbehaving with uprated electronic ignition

[David C]

Fitting a fancy new electronic ignition had the unintended consequence of causing the tachometer on my 410 to vastly over read. This is because the rev counters on early V8s use current sensing loops rather than voltage sensors on newer units.

I chose to update my tacho by replacing the 1960s electronics with a new circuit board made by a company called Spiyda trading on Ebay amongst other outlets. Cost of board about £45. Time to fit about an hour once the unit was out of the car added to about another hour running in a new wire from the coil negative to the tacho.

Instructions are pretty good with helpful videos on YouTube. A major advantage of fitting the new board is that the unit can fairly readily be calibrated during fitment. This is fairly straightforward but requires a mobile phone or laptop with a high level audio output. I struggled a bit as my laptop wouldn't produce enough level.

Nice to have accurate measurement and smoother needle movement.