Tachometer for 912/911

[ttw18]

I am putting the finishing touches on my 912 - 6. I am thinking about how to make the tach work. I am using an MSD6AL and am aware that there is a tach adapter available from our host. I suspect that a 911 tach is calibrated for CDI, but since the 912 did not use CDI I am not sure the adapter would work for me.

[EarlyPorsche]

I have a later tach in my 66 because I used the electromotive distributorless ignition. I would be interested in how to adapt the green tach to my car again.

[tijnes]

Instead of using the tach adapter, you can send out your green tach to get converted to accept a MSD signal. I just had mine done by North Hollywood,it works well and wasn't too expensive. This is a much more elegant solution than using the adapter IMO.

Martijn

[dlague]

how much does that cost may I ask???

[304065]

Call North Hollywood or Palo Alto, they can give you current pricing.

You are right, it doesn't work with a stock tach-- MSD boxes output a 20% duty cycle 12V square wave. VDO tachs take an 11 Volt square wave with a 63% duty cycle-- a 50% duty cycle for a 912.

While you are at it they can rescreen the face or make whatever improvements you require.

I had a tach converted to 10,000 RPM sweep and MSD, it was about $250 if I recall but that was last summer.

The "tach adapter" is basically an induction coil that charges when the points are closed and when they open dumps a couple hundred volts into the tach with plenty of ringing, noise and EMF. Sucks a lot of power and heat, inelegant.

[Howard M]

I switched to an MSD in my '76 2.7 and used the signal line FROM the distributor TO the MSD box for the tach signal. That is how the tach got its signal from the original Permatune box, which had no discrete tach output. By not using the tach output from the MSD I was able to avoid having to use an adapter. I am now using a Pertronix in the distributor and a VDO Memory Tach.