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MG MGB GT V8 Factory Originals Technical - Tach

WHo has converted their stock tach to work with the V8 (ford) engine? How did you do it?
Pimp in a MG

What year tach are you trying to convert? I did mine with a trim pot and fixed resistor in series across the IC chip in a '73 tach, then dialed it in with a pulse generator I built which mimmicks the signal that the tach sees from the coil. Worked really well.

Check the archives for this subject. There was a good post once that had a link to a good web site which covered this mod in detail. All the mods listed are for conversion to a V8, I need the values for a V6 conversion.
Bill Young

Here are the links:

Tony Bates

if youre using a '73 - '80 tach, the modification is the same for a 6 cylinder, and the resistance will be somewhere between 47K ohms and zero. Youll have to adjust it in the same way the V8 one is, by generating a pulse to drive the tach. At 50 Hz it should read 1125 rpm, at 150 Hz it should read 3375 and at 200 Hz it should read 4500 rpm. Hope this helps.

Not owning an osiloscope, I left the wire to the variance resistor loose and just adjusted the resistance 'till I got half the revs ie set the motor until showing 5000 rpm, clip wire in place and adjust resistor to get 2500, remove wire, check, do the same at 2000 etc. Then solder in place when happy. It was around the 20-25 Kohm mark. The only difficulty was the Dill at the electronics shop first sold me a 2kohm then a 100ohm instead of the 100 Kilo ohm variable resistor and caused a some unnecessary confusion and back and forth.
It's still working great.

This thread was discussed between 07/12/2004 and 12/12/2004

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