Tach swap? G13 tach in G10 car?
 

My car is a 1993 1.0L Metro. I want a tach and would rather have the oem tach in the instrument cluster than an add-on tach. But the only car in the salvage with an oem tach is a G13 4-cylinder car. Can a 4-cylinder tach be adapted to a 3-cylinder car?

Pretty sure it's a wiring job.
For example, I have an Integra GSR cluster in my Honda Civic.

Any pics?

If you dig around on teamswift there is a post on there showing what resistors to swap out to get it working on a 3 cyl. It didn't look that hard to do really so it might be worth digging around over there and seeing what is involved in it.

The problem with using a 4 cylinder tach in a 3 cylinder is that the tach reads output from the ignitor and does math.. x/4 = RPM. Lets say x is 4000 on the 4 cylinder, your formula is

4000/4 = 1000 RPM (idle... )

Now, lets assume you put that cluster in your car, and don't change anything about it.

4000/4 = 1000RPM for a four cylinder,
but for the 3 cylinder, the actual formula should be:
4000/3 = 1333.33

So basically, your engine is revving 1330 RPM when your tach is displaying 1000 RPM. The difference won't be linear either... it's a curve.

16000/4 = 4000, 16000/3 = 5333.33.

Now, if you can change caps or resistors to make it do the math correctly, then you're set to go, but just using it without modification will definitely yield an incorrect reading.

Taking it apart and printing out your own label might be an option too, no electronics but a bit of artwork to sort out.
http://opengauge.org/diympggauge/analog/pic5.JPG

Yes, which is why I asked if it could be adapted (to give a correct reading).

And the difference is linear. display=actual * 3/4

Apparently 3 cylinder oem tachs were rare, but not nonexistent.

Just a quick addition the above post, the clear and black plastic have two long screws through them in the upper corners, but that's about it. Also, speedometer calibration is a big PITA.