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MG MGB GT V8 Factory Originals Technical - Convertion of 4 cyl tach to 8cyl

Thanks for reading my post. I have recently done a V8 conversation to a 1980 MGB and can't seem to get a straight answer as to how to convert the tachometer. I have gotten answers from using a potentiator to putting some different diodes in the tach. Can any lend some insight into this process or how to do it properly.

Not long ago this question was asked and several possible answers were proposed. I suggested checking ZAKS MGB V8- Home Page and clicking on
A Better Tach Circuit pics. This works for tachometers from ’77 to ’80 and is what I did. It was very easy and cost only a few bucks. The local Radio Shack didn’t have the right part so I ordered one from an electronics company and it cost about two dollars and the shipping was about three dollars.

Rather than using special equipment to calibrate, I only soldered one terminal, connected the open tachometer to the car with it hanging out of the dash, started the car and ran the idle at two thousand RPM (four thousand on the gauge). Holding the idle steady I connected the other terminal and adjusted new part until it was correct. I checked with and without the part connected a few times to be sure it was right then shut the car off and removed the tachometer to properly solder the second terminal. The job can be done in less than an hour, is as low cost as possible and is as accurate as the original unit.
George Champion

The best way to accomplish that task, is to talk to the experts. contact or call them at 1-800-866-jags They can help you with your tach. It's not expensive if they can do it.
Bill Guzman


I took an SD1 Tacho and put this in the MGB tacho housing. The diameter of the SDi tacho was bigger but the depth and mounting points are exactly the same. Also the scaling itself was the same so i could swap the scale and the tacho needle. Did the same with the speedo but had to cut something of the SD1 scale. Depth was also the same.
Off course swapping a diode is easier but at that ime i didn't know this.

I was just rereading this thread to see what other suggestions you have received to choose from when I saw the hyperlinks I used didn’t work. I’ll try again…
ZAKS MGB V8- Home Page

If it doesn’t work this is the address…

Click on…
A Better Tach Circuit pics
George Champion

I also did my conversion based off the information on "ZAKS MGB V8- Home Page". I also soldered a potemeter (adjustable resistor) onto the tach circuit with some lead wire so I could adjust the tach in the car with it running using a hand held tach as the standard. For the first summer the tach also doubled at my speedometer.
Jim Miller

<<The best way to accomplish that task, is to talk to the experts. >>

Bill, I must disagree. For Richard's '80 MGB, this is aboslutely the easiest part of the whole conversion.

A 100K ohm trimpot with longer leads across pins 3 & 8 on the chip and dial it up match handheld electrical tach. Or, I just soldered in a 470K resistor. It's only off about 300 rpm at 3 grand. This method will have varying results due to the tolerances in the resistor.

Leon Zak's web page was a big help. As was the excellent article in the MGV8 Newsletter(Issue VIII Vol. 1).

You can order a back issue here:

Follow the instructions in the MGv8 Newsletter(issue VIII Vol 1). cost ONE DOLLAR!!!!!

This thread was discussed between 26/03/2002 and 30/03/2002

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